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  • 1. Auda, Yves
    et al.
    Lundin, Erik J.
    Gustafsson, Jonas
    Pokrovsky, Oleg S.
    Cazaurang, Simon
    Orgogozo, Laurent
    A New Land Cover Map of Two Watersheds under Long-Term Environmental Monitoring in the Swedish Arctic Using Sentinel-2 Data2023Inngår i: Water, ISSN 2073-4441, Vol. 15, nr 18, artikkel-id 3311Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A land cover map of two arctic catchments near the Abisko Scientific Research Station was obtained based on a classification from a Sentinel-2 satellite image and a ground survey performed in July 2022. The two contiguous catchments, Miellajokka and Stordalen, are covered by various ecotypes, from boreal forest to alpine tundra and peatland. Two classification algorithms, support vector machine and random forest, were tested and gave very similar results. The percentage of correctly classified pixels was over 88% in both cases. The developed workflow relies solely on open-source software and acquired ground observations. Space organization was directed by the altitude as demonstrated by the intersection of the land cover with the topography. Comparison between this new land cover map and previous ones based on data acquired between 2008 and 2011 shows some trends in vegetation cover evolution in response to climate change in the considered area. This land cover map is key input data for permafrost modeling and, hence, for the quantification of climate change impacts in the studied area.

  • 2. Bjørnø, Jon
    et al.
    van den Berg, Marnix
    Lu, Wenjun
    Skjetne, Roger
    Lubbad, Raed
    Løset, Sveinung
    Performance quantification of icebreaker operations in ice management by numerical simulations2022Inngår i: Cold Regions Science and Technology, ISSN 0165-232X, E-ISSN 1872-7441, Vol. 194Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The paper addresses the problem of quantifying and assessing the effectiveness of icebreaker operations in ice management (IM) using a high-fidelity simulator. The numerical model includes an accurate geometric representation of an icebreaker, a cylindrical protected structure, and a synthetic ice environment. A set of key performance indicators (KPIs) are defined and proposed to quantify the effectiveness of IM strategies for protecting the downstream structure. This give better insight into which IM strategies are more effective with respect to different objectives for certain conditions, thereby enabling better planning and guidance of icebreaker operations. The results from a selection of the simulations performed with nearly 100% ice concentration are presented. This will illustrate the methodology using the different KPIs to quantify the effectiveness and highlight differences between the different IM strategies. From the simulations we see that all patterns have strengths and weaknesses; some KPIs are consistent while others are changing with the ice drift velocity.

  • 3. Bjørnø, Jon
    et al.
    van den Berg, Marnix
    Lu, Wenjun
    Skjetne, Roger
    Lubbad, Raed
    Løset, Sveinung
    Quantifying Icebreaker Performance in Ice Management Operations by High-Fidelity Numerical Simulations2020Inngår i: The 30th International Ocean and Polar Engineering Conference, Virtual, October 2020, Virtual: International Society of Offshore and Polar Engineers , 2020Konferansepaper (Annet vitenskapelig)
    Abstract [en]

    In the study presented in this paper, the problem of quantifying the performance of icebreaker operations within ice management (IM) has been targeted, using the capabilities of high-fidelity simulations by a discrete element simulation model. An accurate geometric and dynamic model of the icebreaker IB Oden, as well as the characterization of a realistic multi-domain ice environment, has been numerically modeled within the simulator. The simulator includes features to easily vary parameters such as ice thickness, ice concentration, floe size distribution, and ice drift velocity and direction. The protected structure is modeled as a cylindrical structure, acting as a measurement probe of the ice loads, ice actions, ice-ice and ice-hull friction resulting from various simulated operations and scenarios. In overall, this give us the tools we need to numerically model, with high fidelity, complex icebreaker operations on realistic ice conditions in order to quantify the performance of IM strategies under various scenarios. This can give us better insight into which IM strategies that are effective, thereby enabling better planning and online guidance of icebreaker operations. INTRODUCTION In recent years the interest for the Arctic has been growing due to the presence of rich natural resources and its strategic location, including the Northern Sea Routes. The design of Arctic offshore structures and marine operations are complicated by the presence of sea ice compared to open water experiences. To ensure a safe operation and design, ice management (IM) is often employed as a risk-reducing measure. This is defined as the sum of all activities from any kind of ice features (Eik, 2008), e.g., protecting a downstream offshore structure from severe ice features by one or more icebreakers. An illustration of the IM concept can be seen in Fig. 1. The IM operation is a complex and integrated system that involves detection, tracking, forecasting, decision making, and eventually handling the detected threatening ice features. When planning such an operation, practical questions such as how many icebreakers that are needed and how to deploy the available icebreaker fleet to most effectively defend an offshore structure, are often addressed based on heuristic data and rather simplified models of icebreaker efficacy. An often used method is the kinematic model by Hamilton et al. (2011a,b) and Hamilton (2011). This model were successfully used in a systematic approach to ice management operations in a full-scale, real-life environment during the Oden Arctic Technology Research Cruise 2015 (OATRC2015) program (Lubbad et al., 2018a; Holub et al., 2018).

  • 4.
    Bolmgren, Karl
    KTH, Rymd- och plasmafysik.
    Time dependence of average structure size and precipitation energy in pulsating aurora2017Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    Pulsating aurora is low intensity aurora appearing in limited structures with quasiperiodicalmodulations in intensity. The highly energetic electron precipitation associatedwith pulsating aurora has been shown to cause chemical changes as far downas the mesosphere, causing ozone depletion. The drivers involved in generating pulsatingaurora are not fully known, and efforts have been made to model many of thesuggested mechanisms. In order to evaluate these results observational constraintson the temporal and spatial characteristics of pulsating aurora are necessary.Previous studies have noted that the pulsating area tends to decrease over timefrom studying single pulsating patches. This study examines a large set of all-skycamera data comprising approximately 400 image series with pulsating aurora fromthe MIRACLE network in northern Fennoscandia in order to determine the time dependenceof the average size and precipitation energy in pulsating aurora. The 20 stime resolution of the all-sky images makes it challenging to identify spatial boundariesof the pulsating structures whose periods have a typical range of 2-20 s. Twomethods are implemented here, with the same results showing a gradual decreasein average size. No relationship between UT and size is clear. The electron precipitationenergies are inferred from the peak emission height and 557,7 nm/427,8 nmintensity ratio, and seem not to be directly related pulsating structure size. Thepeak emission height shows a constant average energy following an initial increasefollowing the onset of the pulsating aurora, and the intensity ratio suggests a constantaverage electron precipitation energy.

  • 5. Bonath, Victoria
    et al.
    Zhaka, Vasiola
    Sand, B.
    Field measurements on the behavior of brash ice2019Inngår i: Proceedings of the 25th International Conference onPort and Ocean Engineering under Arctic Conditions: June 9-13, 2019, Delft, The Netherlands, 2019Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The behavior and properties of brash ice are important issues for the design of ice-going vessels. Heavy brash ice conditions may cause vessels to be dependent on ice-breaker assistance and time delays in the shipping schedule. Brash ice properties are not well studied and full-scale field data are missing in order to verify numerical models on brash ice and broken sea ice in general. The recent study describes new field equipment for testing brash ice and its functionality is tested on brash ice produced by the Swedish Ice-breaker Oden during ice management operations in the Barents Sea. The equipment consists of a big collector, connected to a crane, which is lowered below the brash ice cover. The brash ice mass above is pulled up by the crane and the force required for pulling is measured. A series of 18 field tests were performed and presented. Strengths and weaknesses of the method were evaluated. Ice blocks sizes were measured. The peak load during pull-up was often at least twice the weight of the lifted ice blocks when the blocks were interlocked. For free floating blocks, the peak load conformed to the weight of the blocks.

  • 6. Carrizo, Daniel
    et al.
    Sobek, Anna
    Stockholms universitet, Institutionen för miljövetenskap och analytisk kemi.
    Salvadó, Joan A.
    Stockholms universitet, Institutionen för miljövetenskap och analytisk kemi.
    Gustafsson, Örjan
    Stockholms universitet, Institutionen för miljövetenskap och analytisk kemi.
    Spatial Distributions of DDTs in the Water Masses of the Arctic Ocean2017Inngår i: Environmental Science and Technology, ISSN 0013-936X, E-ISSN 1520-5851, Vol. 51, nr 14, s. 7913-7919Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    There is a scarcity of data on the amount and distribution of the organochlorine pesticide dichlorodiphenyltrichloroethane (DDT) and its metabolites in intermediate and deep ocean water masses. Here, the distribution and inventories of DDTs in water of the Arctic shelf seas and the interior basin are presented. The occurrence of Sigma 6DDT (0.10-66 pg L-1) in the surface water was dominated by 4,4'-DDE. In the Central Arctic Ocean increasing concentrations of DDE with depth were observed in the Makarov and Amundsen basins. The increasing concentrations down to 2500 m depth is in accordance with previous findings for PCBs and PBDEs. Similar concentrations of DDT and DDEs were found in the surface water, while the relative contribution of DDEs increased with depth, demonstrating a transformation over time and depth. Higher concentrations of DDTs were found in the European part of the Arctic Ocean; these distributions likely reflect a combination of different usage patterns, transport, and fate of these compounds. For instance, the elevated concentrations of DDTs in the Barents and Atlantic sectors of the Arctic Ocean indicate the northbound Atlantic current as a significant conveyor of DDTs. This study contributes to the very rare data on OCPs in the vast deep-water compartments and combined with surface water distribution across the Arctic Ocean helps to improve our understanding of the large-scale fate of DDTs in the Arctic.

  • 7. Fenz, Daniel
    et al.
    Younan, Adel
    Piercey, Gerry
    Barrett, John
    Ralph, Freeman
    Jordaan, Ian
    Field measurement of the reduction in local pressure from ice management2018Inngår i: Cold Regions Science and Technology, ISSN 0165-232X, E-ISSN 1872-7441, Vol. 156, s. 75-87Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Local ice pressures are an important design consideration for vessels performing offshore stationkeeping operations, particularly in the late spring and early fall shoulder seasons when they tend to govern over global loading in the development of operating limits. This paper presents analysis of full-scale data that demonstrates the reduction in local pressures provided by ice management. The data was collected during the Oden Arctic Technology Research Cruise in 2015. The distinguishing aspect of this program was the use of two icebreakers, Oden and Frej, which provided the unique opportunity to conduct a full-scale stationkeeping trial in realistic managed ice conditions. Previous local ice pressure data collection programs have occurred during transit in unmanaged ice, ramming of multi-year ice and bergy bit impacts. These have been used to establish recommendations for local design pressures, however they are not completely representative of conditions while stationkeeping in managed ice. In this study the up-crossing rate method was used to analyze local pressure data collected from strain gaged load panels on the Frej’s hull. The results indicate that local pressures from stationkeeping in managed ice are two to four times lower than the transiting cases most analogous to previous data. This provides a sound basis for advocating local design pressures that are lower than current recommendations, and also more representative of actual operating conditions. This can potentially extend the operating envelope of offshore vessels leading to significant savings, while still maintaining limits consistent with accepted risk profiles.

  • 8. Hamilton, Jed
    et al.
    Kokkinis, Ted
    Holub, Curtis
    Matskevitch, Dmitri
    Cheng, Tao
    Harris, Matthew
    Shafrova, Svetlana
    Near-Field Ice Management Tactics for Floating Drilling in Arctic Pack Ice2016Konferansepaper (Annet vitenskapelig)
    Abstract [en]

    In order to be economically viable, Arctic floating drilling in high concentration pack ice requires very high confidence that ice interaction does not lead to costly, unanticipated emergency disconnections of the rig from the well. One of the foremost near-field ice management challenges is to maintain the station-keeping drilling rig within the managed ice channel throughout periods of complex changes in ice drift direction and speed. This entails precise, continuous re-positioning of the ice management fleet, which may be located up to several kilometers up-drift of the station-keeping drilling rig, in response to changing drift. While it may seem plausible to position up-drift ice management operations based on ice drift forecasts, forecasting unfortunately has insufficient precision to achieve the necessary level of reliability. To remedy this problem, ExxonMobil has developed systematic ice management command and control tactics that maintain the station-keeping drilling rig within the managed ice channel with high confidence. The tactics are based solely on the recent drift time history, and therefore eliminate any need for ice drift forecasting for near-field ice management operations. The tactics were proven in a series of near-field ice management tests conducted during the Oden Arctic Technology Research Cruise (OATRC 2015). OATRC2015 was performed by the Norwegian University of Science and Technology in cooperation with the Swedish Polar Research Secretariat and support and participation by ExxonMobil. Over a period of ten days during September, 2015, in which there were many complex Coriolis-driven ice drift loops and cusps and rapid drift direction changes, the methodology was able to successfully manage ice ahead of a fixed way point such that the point remained well within the managed ice channel at all times. The key features of the approach are described herein and include the use of variable length "arched racetrack" icebreaking patterns and an algorithm for continuously adjusting the position and size of the racetracks based on the measured ice drift speed and direction.

  • 9. Hermans, Frederik
    et al.
    Wennerström, Hjalmar
    McNamara, Liam
    Rohner, Christian
    Gunningberg, Per
    All Is Not Lost: Understanding and Exploiting Packet Corruption in Outdoor Sensor Networks2014Inngår i: Wireless Sensor Networks / [ed] Krishnamachari, Bhaskar; Murphy, Amy L.; Trigoni, Niki, Springer International Publishing , 2014, s. 116-132Konferansepaper (Annet vitenskapelig)
    Abstract [en]

    During phases of transient connectivity, sensor nodes receive a substantial number of corrupt packets. These corrupt packets are generally discarded, losing the sent information and wasting the energy put into transmitting and receiving. Our analysis of one year’s data from an outdoor sensor network deployment shows that packet corruption follows a distinct pattern that is observed on all links. We explain the pattern’s core features by considering implementation aspects of low-cost 802.15.4 transceivers and independent transmission errors. Based on the insight into the corruption pattern, we propose a probabilistic approach to recover information about the original content of a corrupt packet. Our approach vastly reduces the uncertainty about the original content, as measured by a manifold reduction in entropy.We conclude that the practice of discarding all corrupt packets in an outdoor sensor network may be unnecessarily wasteful, given that a considerable amount of information can be extracted from them.

  • 10. Heyn, H.
    et al.
    Blanke, M.
    Skjetne, R.
    Ice Condition Assessment Using Onboard Accelerometers and Statistical Change Detection2020Inngår i: IEEE Journal of Oceanic Engineering, ISSN 0364-9059, E-ISSN 1558-1691, Vol. 45, nr 3, s. 898-914Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The presence of sea ice is the predominant risk for ship operations in the Arctic, and monitoring of ice condition around a vessel is crucial during all times of operation. This paper presents a system for online onboard assessment of ice condition. It is demonstrated that ice-induced accelerations in the bow section of the hull follow a bivariate t-distribution and parameters of the distribution have a one-to-one relation to ice condition. This paper suggests a methodology to monitor the ice condition in real time through estimation of parameters that characterize the distribution of hull accelerations. It is shown how a Kullback-Leibler divergence measure can classify ice condition among a set of pretrained conditions. An absolute measure of ice load is suggested as an alternative for situations when pretraining data are not available. The alternative algorithm quantifies the condition through the entropy of measured accelerations. This paper presents a computationally easy methodology and tests against data collected during Arctic transit of an icebreaker. Furthermore, the classification results are compared with the results from two standard methods from machine learning, decision tree and a support vector machine approaches. The results show that the statistical methods provide robust assessment of the prevailing ice conditions, independent of visual and weather conditions. Also, the comparison shows that the statistical classification methods, designed by process knowledge, provide steadier and more reliable results.

  • 11.
    Heyn, Hans-Martin
    et al.
    Norwegian University of Science and Technology, Trondheim, Norway.
    Knoche, Martin
    Technische Universität München, München, Germany.
    Zhang, Qin
    Norwegian University of Science and Technology, Trondheim, Norway.
    Skjetne, Roger
    Norwegian University of Science and Technology, Trondheim, Norway.
    A System for Automated Vision-Based Sea-Ice Concentration Detection and Floe-Size Distribution Indication From an Icebreaker2017Inngår i: International Conference on Ocean, Offshore and Arctic Engineering: Volume 8: Polar and Arctic Sciences and Technology; Petroleum Technology, 2017, Vol. 8Konferansepaper (Annet vitenskapelig)
    Abstract [en]

    This paper presents a ship-mounted multi-lens camera system for sea-ice monitoring and algorithms to automatically evaluate the sea-ice concentration and to indicate the floe-sizes in a radius of 100 meter around the vessel. During the SWEDARCTIC Arctic Ocean 2016 expedition, 11 camera lenses recorded the sea-ice conditions around the Swedish icebreaker Oden. As an example of the possible use of this image system, the images of six lenses are combined into one 360° panoramic image. To distinguish between water and sea-ice in the images, and thus to evaluate the sea-ice concentration around the vessel, a direct thresholding, the k-means, and a novel adaptive thresholding method are applied. Moreover, an edge detector gives the number of pixels that either form the boundary between sea-ice and water or are part of a visible ice fracture. The ratio between these edge pixels and the total number of pixels containing sea-ice gives an indication of the floe size distribution (FSD) in the image.

  • 12. Heyn, Hans-Martin
    et al.
    Skjetne, Roger
    Time-frequency analysis of acceleration data from ship-ice interaction events2018Inngår i: Cold Regions Science and Technology, ISSN 0165-232X, E-ISSN 1872-7441, Vol. 156, s. 61-74Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    During operations with ships in ice-infested waters, vibrations of the hull occur due to ship-ice interaction. The acting ice load and the induced vibrations depend on the ice regime and ice breaking mechanism. Especially crushing of ice against the hull causes high loads against the vessel. The objective of this study is to analyse the frequency components of ice-induced vibrations, measured with accelerometers placed in the bow section of the ship’s hull. The Wigner-Ville distribution, which provides a time-frequency representation, is applied on acceleration data collected on the icebreaker Frej during transit in ice-infested Arctic waters. The resulting time-frequency representations show that the excited frequencies depend on the dominant ice breaking mechanism, on the encounter velocity, and on the position of where the ice interaction against the hull occurs. Furthermore, the natural frequencies of the ship’s hull change slightly, depending on the conditions on the sea-ice around the vessel. It is concluded that a system of distributed accelerometers on a ship can provide information about the acting ice breaking mechanism, the ice conditions around the vessel, and about the location along the hull, where the ship-ice interaction occurs. This can be used as an additional tool in monitoring systems during operations in ice-infested waters.

  • 13. Holub, Curtis
    et al.
    Matskevitch, Dmitri
    Kokkinis, Ted
    Shafrova, Svetlana
    Near-field ice management tactics - Simulation and field testing2018Inngår i: Cold Regions Science and Technology, ISSN 0165-232X, E-ISSN 1872-7441, Vol. 156, s. 23-43Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Robust near-field ice management tactics have been developed for use in Arctic floating drilling. The tactics provide high confidence that a station-keeping drilling rig can be kept within the managed ice channel throughout periods of complex changes in ice drift direction and speed, and thus effectively mitigate the potentially high economic cost of an emergency disconnection. Kinematic simulations were used to design the systematic arched racetrack tactics which were implemented and tested during the Oden Arctic Technology Research Cruise 2015 (OATRC2015) conducted in the pack ice north of Svalbard at about 82°N latitude and 16°30'E longitude. The long duration field tests, conducted over 10 days using two icebreakers, show the virtual drilling rig was maintained within the managed ice channel in complex ice drift conditions that included multiple ice drift loops, cusps, and reversals. Moreover, the field observations, including satellite and helicopter imagery, confirm the fundamental simulation methods. The field results are extended through simulations to assess the impact of icebreaker fleet configuration and capability on outlet ice conditions (floe size and brash content) and the performance of the tactics against long-term ice drift records (over 1200 days with over 18,000 km of drift). Results demonstrate the importance of systematically executing the tactics and confirm that the geostationary drilling rig is kept within the managed ice channel.

  • 14.
    Holub, Curtis
    et al.
    Exxon Mobil Upstream Research Company.
    Matskevtich, Dmitri
    Exxon Mobil Upstream Research Company.
    Yanni, Victor Garas
    Exxon Mobil Upstream Research Company.
    Shafrova, Svetlana
    Exxon Mobil Upstream Research Company.
    Kokkinis, Ted
    Exxon Mobil Upstream Research Company.
    Ice Drift Tracking Using Photogrammetric Methods on Radar Data2017Konferansepaper (Annet vitenskapelig)
    Abstract [en]

    Ice drift measurements are needed to support ice management and navigation in arctic and sub-arctic regions where pack ice and/or icebergs are present. A method is described which can provide real time measurement of ice drift during operations, or can be used to analyze historical radar records. The method measures ice movement by applying photogrammetric feature detection and matching algorithms to marine radar or synthetic aperture radar (SAR) satellite data. The method is demonstrated through analysis of marine radar and SAR satellite data collected during the Oden Arctic Technology Research Cruise 2015 (OATRC 2015).

  • 15. Kjerstad, Oivind K.
    et al.
    Lu, Wenjun
    Skjetne, Roger
    Loset, Sveinung
    A method for real-time estimation of full-scale global ice loads on floating structures2018Inngår i: Cold Regions Science and Technology, ISSN 0165-232X, E-ISSN 1872-7441, Vol. 156, s. 44-60Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper proposes an algorithm that uses conventional measurements found on-board ships coupled with additional Inertial Measurement Units to estimate the motions and global loads acting on them. The work is motivated by the scarce availability of full-scale load data for sea-ice operations and by the invasive instrumentation of strain gauges used to obtain global loads of all degrees of freedom. Full-scale data are key to a number of design, operational, and research aspects related to sea-ice operations. The proposed algorithm is based on four Inertial Measurement Units (IMUs) that together with position and heading measurements are used to make estimates of dynamic linear and rotational acceleration (acceleration resulting in motion). We show how to use models updated with propulsion and wind measurements to estimate propulsion, hydrodynamic, wind, and ice loads through a setup catering to real-time implementation. A case study with the Swedish icebreaker Oden is presented and discussed. The algorithm effectively yields reasonable ice load history estimations and presents great potential in its further application to real-time global ice load estimations.

  • 16. Kramers, Job
    Global ice ridge ramming loads based on full scale data and specific energy approach2016Independent thesis Advanced level (degree of Master (Two Years))Oppgave
    Abstract [en]

    This thesis analyses the loads that occurred during an ice ridge ramming experiment with the icebreaker Oden. Sea ice ridges are formed due to breaking and deformation of the ice cover. Wind, current, thermal expansion and Coriolis forces induce compression and shear forces onto level ice which can break the ice into rubble. The blocks of ice rubble are pushed together, forming a wall of broken ice in hydrostatic equilibrium. This wall of broken ice forced up by pressure is defined as an ice ridge. In general ice ridges are long, nonsymmetrical, curvilinear features with a wide variability of sizes and shapes. In Arctic regions, sea ice ridges are often used to calculate the design load in the absence of icebergs. Ice ridges also play a major role in icebreaker efficiency, since an icebreaker might need several ‘rams’ to break through an ice ridge. Ice ridge actions on icebreakers are not completely understood. Complex ice behavior under rapidly applied stress, and the complex geometries of the bodies in contact makes it a challenging research topic. The dynamic behavior of the vessel during the ramming can be used to make an estimate of the ice loads that occurred. This thesis analyses the ice load that occurred during a ridge ramming experiment that was performed with icebreaker Oden during the ODEN AT research cruise project in 2013. To advance our understanding in the global ice ridge ramming loads, twomodels were developed: 1) a simulationmodel using the Specific Energy Absorption (SEA) of mechanical crushing of ice to calculate the global ice loads, 2) a load identification model using full-scale data to determine the global ice loads. The simulation model was developed to enhance the understanding of relevant physical phenomena and parameters. During this process, specific energy principles of crushing of ice were identified as a promising although relatively unknown method for impact dynamics into ice. The Specific Energy Absorption (SEA) of mechanical crushing of ice is defined as the energy per unit mass of crushed ice, necessary to turn solid ice into crushed (pulverized) material. Besides the SEA value, the penetration velocity, density of ice, and volume of crushed ice, are required to calculate the ice load. A contact model was developed to determine the load location and direction on the hull. The icebreaker Oden is represented by a nonlinear mass-damper-spring system. Maneuvering theory is applied, which means that the hydrodynamic variables are estimated at one frequency of oscillation. In the simulation model, a known thrust force is applied on the vessel, making it move forward in open water, and then penetrate the ice ridge. The simulation model calculates the ice loads and vessel’s motions (i.e. accelerations, velocity, and displacement). The load identification model combines the Kalman filter and a joint input-state estimate algorithm to estimate the state- and excitation vector from acceleration, velocity and displacement data in 3DOF (i.e. surge, heave, pitch). The joint input-state estimate algorithm combines measured data with an estimate of the state of the system in a way that minimizes the error. The full-scale data analyzed in this thesis includes a profile of amulti-year ice ridge, vessel characteristics, acceleration data from a motion reference unit (MRU), GPS data, and propulsion data. From the results of the load identification model, we conclude that the current combination of model and data does not provide sufficient information to estimate the global ridge ramming loads with high reliability. The main reasons for this are the absence of additional MRU(s), the low sample frequency of the MRU, the data uncertainty, and the simplified hydromechanics. However, the suggested approach to calculate the global ice loads is reliable as long as the data is valid. This is verified by recalculating the ice loads from the data (i.e. motions), generated by the simulation model. Results indicate that the specific energy approach can be used to simulate an impact of a vessel into an ice ridge, under assumption that the ice fails purely due to crushing. This assumption is only valid during the beginning of the impact, as other failure modes often start to dominate as the penetration of the vessel into the ridge increases.

  • 17.
    Krützfeldt, Jari
    KTH, Marina system.
    Development of a System for Long Term Underwater Sensing2015Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    The monitoring of the worlds oceans is a fundamental requirement to understand and predict the ongoing climate change. Scientists need reliable long-term data series from regions that are of great interest for understanding the climate change and its consequences. An important area is the West Antarctic Ice Shelf (WAIS), which is still a great uncertainty of future sea level rise predictions. The vulnerable polar regions are, however, seldom sampled, mainly because of their remoteness, the cost and the possibility to reach them.The KTH Center of Naval Architecture recently formed a cooperation with the Department of Earth Science (GVC) at the University of Gothenburg to develop a cost effective sens-ing system, designed to acquire long term temperature data in remote polar regions. The oceanographers at GVC are researching if the sea bottom temperature in shelf regions like the WAIS can be used as a proxy for the whole oceanic heat content. This research makes it possible to use sensing systems that are moored close to the sea-floor and measure ocean bottom temperature only.In this thesis a low-cost system for long term underwater sensing (LoTUS) is developed. The LoTUS bottom lander system consists of a positive buoyant pressure hull equipped with a very precise temperature sensor, an Iridium satellite link, GPS and a deep hibernation functional-ity. The bottom landers are deployed from a ship or a helicopter and sample data for up to 10 years in water depths up to 1000 meter. As soon as the intended operation time is reached, the LoTUS lander releases its anchor, surfaces and transmits its temperature data to the user ashore via satellite. Afterwards the bottom lander reconfigures to a GPS beacon mode, i.e. it drifts and regularly sends out its position to observe direction and velocity of surface currents. The LoTUS system was successfully tested in the Baltic Sea and in the Petermann 2015 Ex-pedition in northern Greenland. The bottom landers proved to be working under harsh polar conditions and can be used as a new and innovative low cost sensing system to acquire long term temperature data.

  • 18.
    Kugelberg, Edvin
    et al.
    KTH, Skolan för industriell teknik och management (ITM).
    Andersson, Oscar
    KTH, Skolan för industriell teknik och management (ITM).
    Wind Vector Estimation by Drone2020Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    An original approach for measuring wind speed and direction by the use ofdrones was proposed and compared to an existing one. The original approach allowed the drone to drift with the wind and use the translatory velocity for input into a non-linear estimator, while the existing approach used a stationary hovering drone and its tilt for input to an estimator.

    A simulation environment was set up in Simulink and Matlab and validated using outputs from previous researchers performing similar tasks. The first test exposed the two approaches to wind tunnel-like environment with a strictly horizontal wind, while the second test used real wind data collected on-board a meteorological research vessel. Results showed that the original approachperformed better for estimating both direction and speed, but it required a largearea to drift in during operation.

  • 19. Langer, Sarka
    et al.
    Österman, Cecilia
    Strandberg, Bo
    Moldanová, Jana
    Fridén, Håkan
    Impacts of fuel quality on indoor environment onboard a ship: From policy to practice2020Inngår i: Transportation Research Part D: Transport and Environment, ISSN 1361-9209, E-ISSN 1879-2340, Vol. 83Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Environmental considerations, concerning the negative impacts of ship exhaust gases and particles on ambient air quality, are behind the requirements of cleaner marine fuels currently applied in designated emission control areas (ECAs). We investigated the impact of a ship operating on two types of fuel on the indoor air quality onboard. Gaseous and particulate air pollutants were measured in the engine room and the accommodation sections on-board an icebreaker operating first on Heavy Fuel Oil (HFO, 1%-S), and later Marine Diesel Oil (MDO, 0.1%-S). Statistically significant decrease of SO2, NOx, PM2.5 and particle number concentration were observed when the ship was operating on MDO. Due to the higher content of alkylated PAHs in MDO compared to HFO, the concentration of PAHs increased during operation on MDO. The particulate PAHs classified as carcinogens, were similar to or lower in the MDO campaign. Chemical analysis of PM2.5 revealed that the particles consisted mainly of organic carbon and sulfate, although the fraction of metals was quite large in particles from the engine room. Principal Component Analysis of all measured parameters showed a clear difference between HFO and MDO fuel on the indoor environmental quality on-board the ship. This empirical study poses a first example on how environmental policy-making impacts not only the primary target at a global level, but also brings unexpected localized benefits at workplace level. The study emphasizes the need of further investigations on the impact of new marine fuels and technologies on the indoor air environments on board.

  • 20.
    Leijonhufvud, Wilhelm
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser.
    Marknadsanalys över tekniska lösningar för avsyning av lavinterräng samt ett analysverktyg för att förstå hur och var laviner har gått2020Independent thesis Basic level (university diploma), 80 poäng / 120 hpOppgave
    Abstract [sv]

    I Kiruna kommun mellan Abisko - Björkliden, på berget Nuoljas ostliga sluttning går det ett flertal laviner varje säsong. Sedan 2013 har Trafikverket installerat ett lavinbekämpningssystem bestående av Gazex kanoner som med en stor smäll startar kontrollerade laviner. Genom regelbunden sprängning motverkar man att större snömassor byggs upp och därmed tar man bort risken för stora laviner att gå. Stora laviner riskerar att nå fram till väg- och järnvägen och kan medföra längre stopp för malmtrafiken.

    Före varje sprängning vill man vara säker på att varken människor eller djur befinner sig i terrängen, idag gör man en visuell bedömning innan man inleder en sprängning. Genom ny teknik kan man säkerhetsställa att ingen befinner sig i riskzonen vilket gör att sprängningen kan ske med större säkerhet.

    Rapporten har belyst olika tekniker som radar, drönare och infraröda rörelsedetektorer och hur dessa kan implementeras på Nuolja. Drönare används mer och mer runt om i världen tack vare deras mångsidiga användningsområden. Att använda en drönare för att skanna lavinterräng är tideffektivt men inte optimalt i alla väderförhållanden. IR-rörelsedetektorer är ett annat alternativ som med stor precision känner av den minsta rörelsen från djur eller människor. Till följd av undersökningen av industrier och skidanläggningar runt om i världen (bland annat alperna och Nordamerika) kan man dra slutsatsen, att radar är det som används för att hitta människor och djur i lavinterräng.

    Rapporten behandlar även ett analysverktyg som efterfrågades av Trafikverket avseende hur man kan studera och analysera laviner som har gått. Med LiDAR-Laser kan man få fram samma underlag och information som lavintekniker får genom fältundersökningar. Med LiDAR får man aktuell information från ett säkert avstånd vilket minskar exponeringen av personal i riskzonen. Man kan även använda LiDAR för att studera snötäcket i förebyggande arbete mot laviner.

    Fulltekst (pdf)
    FULLTEXT01
  • 21. Lu, Wenjun
    et al.
    Heyn, Hans-Martin
    Lubbad, Raed
    Løset, Sveinung
    A large scale simulation of floe-ice fractures and validation against full-scale scenario2018Inngår i: International Journal of Naval Architecture and Ocean Engineering, ISSN 2092-6782, E-ISSN 2092-6790, Vol. 10, nr 3, s. 393-402Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    While interacting with a sloping structure, an ice floe may fracture in different patterns. For example, it can be local bending failure or global splitting failure depending on the contact properties, geometry and confinement of the ice floe. Modelling these different fracture patterns as a natural outcome of numerical simulations is rather challenging. This is mainly because the effects of crack propagation, crack branching, multi fracturing modes and eventual fragmentation within a solid material are still questions to be answered by the on-going research in the Computational Mechanic community. In order to simulate the fracturing of ice floes with arbitrary geometries and confinement; and also to simulate the fracturing events at such a large scale yet with sufficient efficiency, we propose a semi-analytical/empirical and semi-numerical approach; but with focus on the global splitting failure mode in this paper. The simulation method is validated against data we collected during the Oden Arctic Technology Research Cruise 2015 (OATRC2015). The data include: 1) camera images based on which we specify the exact geometry of ice floes before and after an impact and fracturing event; 2) IMU data based on which the global dynamic force encountered by the icebreaker is extracted for the impact event. It was found that this method presents reasonably accurate results and realistic fracturing patterns upon given ice floes.

  • 22. Lu, Wenjun
    et al.
    Heyn, Hans-Martin
    Lubbad, Raed
    Løset, Sveinung
    Large scale simulations of floe-ice fractures and validation against full-scale data2017Inngår i: POAC 2017: Proceedings of the 24th International Conference on Port and Ocean Engineering under Arctic Conditions, 2017Konferansepaper (Annet vitenskapelig)
    Abstract [en]

    While interacting with a sloping structure, an ice floe may fracture in different patterns. For example, it can be local bending failure or global splitting failure depending on the contact properties, geometry and confinement of the ice floe. Modelling these different fracture patterns as a natural outcome of numerical simulations is rather challenging. This is mainly because the effects of crack propagation, crack branching, multi fracturing modes and eventual fragmentation within a solid material are still questions to be answered by the on-going research in the Computational Mechanic community. In order to simulate the fracturing of ice floes with arbitrary geometries and confinement; and also to simulate the fracturing events at such a large scale yet with sufficient efficiency, we propose a semi-analytical/empirical and semi-numerical approach; but with focus on the global splitting failure mode in this paper. The simulation method is validated against data we collected during the Oden Arctic Technology Research Cruise 2015 (OATRC’15). The data include: 1) camera images based on which we specify the exact geometry of ice floes before and after an impact and fracturing event; 2) IMU data based on which the global dynamic force encountered by the icebreaker is extracted for the impact event. It was found that this method presents reasonably accurate results and realistic fracturing patterns upon given ice floes.

  • 23. Lu, Wenjun
    et al.
    Lubbad, Raed
    Loset, Sveinung
    Parallel channels’ fracturing mechanism during ice management operations. Part II: Experiment2018Inngår i: Cold Regions Science and Technology, ISSN 0165-232X, E-ISSN 1872-7441, Vol. 156, s. 117-133Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    During ice management operations, cutting parallel channels with narrow spacing in the ice using icebreakers can effectively reduce the size of ice floes reaching the protected vessel/structure. A narrow channel spacing width generates smaller ice floes. However, a spacing that is too narrow can lead to excessive or even impractical ice management operations. Therefore, it is beneficial to establish a theoretical model that correlates the channel spacing width with the frequency of ice fracturing events and the reduction of managed ice floe sizes. This is achieved in the current study with two sequential papers, i.e. Papers I and II. In Paper I, a theoretical model involving an "edge crack model" was formulated to predict the following conditions for an ice management operation: 1) the maximum ice floe with size LMCD that can be produced; 2) the maximum channel spacing width hmax beyond which long cracks will not develop between the channels; and 3) the required force to initiate long cracks between parallel channels. In this paper (Paper II), we describe two dedicated "parallel channel tests" conducted separat"ely on September 26th and 29th in 2015 during an expedition to the Arctic Ocean (around 82°N and 16°E) with the icebreakers Oden and Frej. The tests had "well-controlled" channel spacing in each test run. Several different channel spacing values were tested with the Oden and the consequent fracturing information was documented by camera images. Image processing enabled us to extract information, such as maximum floe sizes and floe size distributions, given different channel spacing widths. In addition, the ship’s data, such as ship velocity and propulsion history, enabled us to validate the theoretical model’s capability to predict the onset of long cracks between two parallel channels. Despite uncertainties (e.g., non-uniform ice thickness, fracture properties of sea ice, etc.) involved in the tests, favourable comparisons between the experimental results and the theoretical predictions were achieved. Both the theoretical model and experimental results help clarify the parallel channel fracturing mechanism.

  • 24. Lu, Wenjun
    et al.
    Lubbad, Raed
    Løset, Sveinung
    Skjetne, Roger
    Parallel Channel Tests During Ice Management Operations in The Arctic Ocean2016Konferansepaper (Annet vitenskapelig)
    Abstract [en]

    During ice management operations, creating narrow parallel channels with icebreakers can effectively reduce ice floe sizes for the protected vessel/structure. Yet too narrow channel spacing requirement shall lead to excessive or even unpractical ice management operations. Empirical experience shows an almost 1:1 relationship between ‘downstream floe size’ and ‘parallel channel spacing’ while designing an ice management operation. However, before this paper, there exists no dedicated parallel channel tests with strictly controlled channel spacing and sufficient instrumentation to quantify such relationship. In this paper, we report two parallel channel tests, which have been conducted in September 2015 during an expedition to the Arctic Ocean with icebreakers, Oden and Frej. During the test, helicopter images and an onboard camera were utilised to document the parallel channel fracturing events. With the collected data, we strive to quantify if there is a prominent relationship between parallel channel spacing and the corresponding managed ice floe size. In order to analyse the floe size distribution and its relationship with channel spacing from helicopter images, we developed an image segmentation method that propagates visually identifiable seeding cracks in the image. In addition, onboard camera images were utilised to yield the frequency of parallel channel fracturing events. Given the ice conditions and Oden's specific structural form, with all the different channel spacing tested, it turned out that a channel spacing over 200 m would already prohibit the development of parallel channel fracturing events. Most of the observed events take place when the spacing is smaller than around 100 m. In addition, as was expected, more frequent fractures are taking place with narrower channel spacing, e.g., distances smaller than 30 m. The relationship between managed ice floe size and channel spacing are studied. It is found that almost all (100%) of the produced downstream floe sizes are smaller than twice the channel spacing; 90% of them are smaller than 1.5 times of the spacing; and the majority of them (from 46% to 80%, depending on the spacing distance) are smaller than 1 time of the channel spacing. With such quantified relationships, we can practically estimate the size of the managed ice floes based on known/expected channel spacing.

  • 25. Lu, Wenjun
    et al.
    Lubbad, Raed
    Shestov, Aleksey
    Loset, Sveinung
    Parallel channels’ fracturing mechanism during ice management operations. Part I: Theory2018Inngår i: Cold Regions Science and Technology, ISSN 0165-232X, E-ISSN 1872-7441, Vol. 156, s. 102-116Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    It is frequently observed that long cracks in sea-ice tend to form between parallel channels during ice management operations. The long cracks that develop play an important role in reducing the size of the managed ice floes, which is one of the main goals in an ice management operation. However, the fracture mechanism behind these long cracks remains unclear. To address this issue, a comprehensive study is reported here in two associated papers. In the current paper (i.e., Paper I), an edge-crack theoretical model is proposed to elucidate the parallel channels’ fracture mechanism. The proposed theoretical model is partially based on theories regarding ship - level ice interactions and partially based on previous studies on the general ice fracturing mechanism. The edge-crack theoretical model is extensively examined using a separately developed numerical scheme based on the eXtended Finite Element Method (XFEM), which allows for the existence of a singularity field and displacement jump within conventional Finite Elements (i.e., FEM). The numerical scheme is benchmarked against known asymptotic analytical solutions and field experiments. Afterwards, with the developed numerical scheme, through fitting numerical simulation results in terms of the edge crack’s Stress Intensity Factors (SIFs) and a relevant asymptotical analysis, we managed to derive a group of closed-form formulae with wide application ranges. For the current engineering problem, this set of formulae quantifies the maximum parallel channel spacing hmax, beyond which the observed parallel channels’ fracturing events cease to occur. Moreover, the same numerical scheme is utilised to study parallel channels’ fracturing paths. Based on the XFEM-based crack path simulations, a second group of formulae and a numerical recipe were obtained to characterise a simplified crack path. This set of equations enables us to quantify the maximum floe size LMCD that can be generated between two parallel channels and its corresponding floe size ratio. In the sequel paper (i.e., Paper II), these equations are validated by a series of well-controlled field experiments undertaken during the Oden Arctic Technology Research Cruise of 2015 (OATRC2015).

  • 26. Lu, Wenjun
    et al.
    Zhang, Qin
    Lubbad, Raed
    Løset, Sveinung
    Skjetne, Roger
    A Shipborne Measurement System to Acquire Sea Ice Thickness and Concentration at Engineering Scale2016Konferansepaper (Annet vitenskapelig)
    Abstract [en]

    Sea ice concentration and thickness are important parameters for the calculations of ice actions and their effects on Arctic offshore structures and for the evaluation of icebreaker performance. Various methods exist nowadays to monitor these parameters, ranging from geophysical scale to local scale. During the Oden Arctic Technology Research Cruise 2015 (OATRC’ 15), we installed both Ice Concentration and Ice Thickness cameras and developed corresponding algorithms to achieve real time quantification of ice concentration and visual estimation of ice thickness information. For the ice concentration analysis, we utilized both the global Otsu method to categorize an image into two regions (black water and white ice); and the K-means method to identify more regions based on the gray scale from the image. With the methods, we conducted a case study by analyzing the ice concentration in a selected time window. In the case study, we include both dry ice (in white color) and wet ice (in gray color, generally composed of ice rubbles, young ice, and melt ponds) as ice region for the K-means method. The K-means method yields higher ice concentration values in comparison to the global Otsu method, in which, melt ponds/young ice was frequently mistaken as open water. It turns out that the K-means method enables more flexibility to cope with the complicated ice environment by separating the image into more regions that can be included as ice in an ice concentration analysis. For the ice thickness camera, the intention was to capture the events while a broken ice piece is tilted, next to the ship side, and expose its thickness region to the camera. In this paper, we developed an automatic tracking algorithm to sift these events out from all the images taken by the Ice Thickness acquisition system. After projecting a grid with physical length onto the image, the ice thickness information can be visually quantified. We compared the ice thickness obtained from the Ice Thickness camera and that obtained by an Electro-Magnetic inductive device in a selected time window. The results agree well with each other. Considering the advantages and disadvantages of each method, this demonstrates the benefits of combining redundant approaches for obtaining the ice thickness information with a higher degree of confidence.

  • 27. Lubbad, Raed
    et al.
    Loset, Sveinung
    Lu, Wenjun
    Tsarau, Andrei
    van den Berg, Marnix
    An overview of the Oden Arctic Technology Research Cruise 2015 (OATRC2015) and numerical simulations performed with SAMS driven by data collected during the cruise2018Inngår i: Cold Regions Science and Technology, ISSN 0165-232X, E-ISSN 1872-7441, Vol. 156, s. 1-22Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In the autumn of 2015, the Norwegian University of Science and Technology (NTNU) and the Swedish Polar Research Secretariat (SPRS) performed a research cruise named the "Oden Arctic Technology Research Cruise 2015" (OATRC2015); it involved the two Swedish icebreakers, Oden and Frej, in the international waters north of Svalbard. The ExxonMobil Upstream Research Company supported and participated in OATRC2015. The overall objective of OATRC2015 was to perform a safe cruise, collect valuable and important scientific data, and conduct full-scale field trials to test key technologies. The scientific scope of OATRC2015 included three major fields of study, namely: 1) collection of full-scale data necessary to build, calibrate and validate numerical models for floaters in ice, 2) collection of full-scale data necessary to build, calibrate and validate numerical models for ice management operations, and 3) collection of data for health, safety and environmental research. This paper presents OATRC2015, including the objectives of the expedition, and provides an overview of the research performed and the major findings. In addition, the paper includes an extensive discussion on the use of full-scale data from OATRC2015 to validate the Simulator for Arctic Marine Structures (SAMS).

  • 28. Lubbad, Raed
    et al.
    Løset, Sveinung
    Hedman, Ulf
    Holub, Curtis
    Matskevitch, Dmitri
    Oden Arctic Technology Research Cruise 20152016Konferansepaper (Annet vitenskapelig)
    Abstract [en]

    In the autumn of 2015, the Norwegian University of Science and Technology (NTNU) and the Swedish Polar Research Secretariat (SPRS) performed a research cruise, named the "Oden Arctic Technology Research Cruise 2015" (OATRC2015) involving the two Swedish icebreakers Oden and Frej in the international waters north of Svalbard. The ExxonMobil Upstream Research Company supported and participated in OATRC2015. The overall objective of OATRC2015 was to perform a safe cruise collecting valuable and important scientific data and to conduct full-scale field trials for testing of key technologies. The scientific scope of OATRC2015 included three major fields of studies, namely: 1) collection of full-scale data necessary to build, calibrate and validate numerical models for floaters in ice, 2) collection of full-scale data necessary to build, calibrate and validate numerical models for Ice Management operations, and 3) collection of data for health, safety and environmental research. This paper presents OATRC2015, including the objectives of the expedition, and provides an overview of the performed research and the major findings. Several companion ATC 2016 papers are complementary to this paper.

  • 29. Massey, D.
    Numerical Simulation of Ice-Rubble Mound Breakwater Interactions2018Independent thesis Advanced level (degree of Master (Two Years))Oppgave
    Abstract [en]

    Offshore activity in energy production, fishing, shipping, and tourism is projected to increase in the Arctic and Sub- Arctic. This projected increase in offshore activity means the supporting coastal infrastructure needs to be expanded. All human activity in ice-prone regions requires a specialized knowledge and understanding of ice mechanics and how to properly design against ice forces and ice-structure interactions. Analyzing ice-structure interactions is a prerequisite for any successful venture into areas where sea ice can occur. This thesis studied numerically modeling the interaction between pre-broken, rigid ice sheets and wide, sloping structures. The thesis focused on adapting a numerical model and validating the base phenomena of the simulated ride-up and pile-up. 

    The numerical model used in this study is the Simulator for Arctic Marine Structures (SAMS). SAMS has previously been validated for ship-shape structures, and individual modules within SAMS has been validated for a wider range of applications. However, coastal structures with wide, upward slopes were previously unanalyzed, and SAMS required a few modifications before simulations could proceed. Due to limitations in the version of SAMS used for this study, level sheet ice was approximated with a section of pre-broken, rigid bodies being driven by a significantly larger, unbroken sheet. Ice was driven by simulated current and wind, thus a limit-force scenario could theoretically be reached. Side confinement was used to reduce the three dimensional (3D) effects introduced in the rigid-body approximation. 

    For ride-up, 36 test conditions were used with ice thicknesses between 0.5 and 1 m, velocities between 1.0 and 2.0 m/s, and the slopes of 1:4 to 1:6. Each test combination was repeated 40 times for a total 1440 simulations. Results from the tests show ride-up is both qualitatively and quantitatively well represented with an 18.9% difference between the simulations and Christensen's analytical model for ride-up. 

    For pile-up, 22 tests conditions were used with values similar to those found in the North Caspian Sea. The ice thickness was 0.15 m, the velocity was 0.5 m/s, and the slope was 1:3. Simulations were designed to test the effects of ice-ice friction, ice-structure friction, and rubble geometry on the pile-up behavior of SAMS. Qualitatively, pile- up simulations showed 5 distinct stages of simulation: 1) initial ride-up, 2) initial pile-up, 3) rubble-pile development, 4) ice-sheet failure away from the pile, and 5) the unbroken ice sheet directly influencing the pile. Stages 1-3 correspond with the expected behavior of pile-up, but stages 4 and 5 represent unrealistic behavior caused by the rigid-body approximation. Quantitatively, ice loads ranged between 3 and 9 kN/m, porosity between 0.35 and 0.65, the pile sail from 1-3 m, and the pile keel was not consistently grounded. Sensitivity tests have shown pile-up in SAMS is: 1) sensitive to changes in ice-ice friction for lower friction coefficients and relatively insensitive for higher friction coefficients, 2) small increases in ice-structure friction can exaggerate the aberrant stages, and 3) triangular rubble geometry can exaggerate the aberrant stages.

  • 30. Matskevitch, Dmitri
    et al.
    Løset, Sveinung
    Shafrova, Svetlana
    Mitchel, Douglas
    Holub, Curtis
    Application of Satellite Remote Sensing Data during OATRC 2015 Research Expedition2016Konferansepaper (Annet vitenskapelig)
    Abstract [en]

    The Norwegian University of Science and Technology (NTNU), in collaboration with the Swedish Polar Research Secretariat (SPRS), conducted the "Oden Arctic Technology Research Cruise" (OATRC2015) in the autumn of 2015. The ExxonMobil Upstream Research Company (EMURC) supported and participated in OATRC2015, as further described in a 2016 ATC companion paper by Lubbad et al. (2016). The main objectives of OATRC2015 expedition, conducted in the Arctic Ocean North of Svalbard, included collection of full-scale data for modelling floaters in ice and collection of full-scale data for modelling ice management operations. Amongst other research, satellite remote sensing technology was used extensively to support the ice management objectives: (1) preparation for the expedition and site selection; (2) monitoring of ice conditions and results of the trials during the expedition; (3) and ice monitoring in the trials area after the expedition. Both publically and commercially available satellite data were acquired and analyzed. The paper discusses the role and the importance of satellite remote sensing data in organizing and executing the ice management research as well as challenges associated with satellite data acquisition, interpretation and timely delivery to the vessels operating at 82°N. The satellite data used at different stages of OATRC2015 expedition covers a wide spectrum ranging from ultra-high resolution images (e.g. WorldView 3 optical satellite imagery with 30 cm resolution and CosmoSkyMed X-band radar satellite imagery with 1 m resolution) to publically available low-resolution AQUA/TERRA MODIS optical satellite imagery with 250 m resolution and 50m resolution Sentinel-1 C-band radar imagery. Approximately 230 satellite images were acquired and analyzed in support of OATRC2015.

  • 31. Mike, Manuel
    et al.
    Freeman, Ralph
    I. J., Jordaan
    Using the Event Maximum Method to Further Analyze Full Scale Local Pressure Data2016Konferansepaper (Annet vitenskapelig)
    Abstract [en]

    Extreme values for local ice pressure are a primary consideration in the design of local structure for ships and offshore structures in arctic environments. ISO 19906 (2010) includes guidelines for a probabilistic approach in determining the local design pressure for Arctic offshore structures. However, the standard is vague in how it should be used. The probabilistic method employed in the standard is the event maximum method developed by Jordaan et al. (1993). It accounts for the expected exposure of the local structure to ice pressure and includes a constant, a, used to describe the relationship between local pressure and area. The constant a is derived in Jordaan et al. (1993) and extended in Jordaan et al. (1997) and reported in Taylor et al. (2010). The a-area relationship is based on the local pressure values from the very aggressive multi-year ridge rams of the CANMAR Kigoriak trial (1982). This leads to a very conservative a-area relationship and may be excessive for some ice conditions. This paper includes an explaination of the use of the event maximum method in ISO 19906. Local pressure data obtained through shear strain gauge systems from Polar Sea (1983) and Oden (1991) have been reanalyzed using the event maximum method (Jordaan et al. 1993, 1997). The data has been sorted by both ice thickness and ice concentration to investigate the existence of a trend between ice thickness and local pressure.

  • 32. Mitchell, Douglas A.
    et al.
    Shafrova, Svetlana
    Application of a free drift tactical ice forecast model in pack ice conditions2018Inngår i: Cold Regions Science and Technology, ISSN 0165-232X, E-ISSN 1872-7441, Vol. 156, s. 88-101Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The extension of oil and gas exploration in High Arctic offshore locations will likely require floating drilling capability in the presence of high-concentration sea ice (pack ice) at the beginning and end of the open water season. The detection and drift forecasting of potentially unmanageable ice features (PUIF) will be key components of an ice management system designed to manage risk while drilling during pack ice intrusions. In September 2015 during the Oden Arctic Technology Research Cruise 2015 (OATRC 2015), an ExxonMobil Upstream Research Company (EMURC) free drift tactical ice forecast model designed to forecast the drift of individual ice floes in low concentration ice conditions was applied in near real-time to high concentration pack ice with predominant thicknesses of medium first-year ice in the Arctic Ocean. The description and application of the proposed ice drift forecast model is presented in this paper. In addition, forecast results are compared to drift data collected during OATRC 2015. It is shown that the free drift forecasting tool produces reasonably accurate and useful forecasts in the high concentration ice observed.

  • 33. Nilsson, Hampus
    et al.
    Pilesjö, Petter
    Hasan, Abdulghani
    Persson, Andreas
    Dynamic spatio-temporal flow modeling with raster DEMs2021Inngår i: Transactions on GIS, ISSN 1361-1682, E-ISSN 1467-9671, Vol. n/a, nr n/aArtikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A user-friendly high-resolution intermediate complexity dynamic and spatially distributed flow model is crucial in urban flood modeling. Planners and consultants need to improve the accuracy of floods and estimation of risks. A new flow model will serve as a rapid tool to improve identification of these. This article provides a detailed explanation of a model based on a multiple flow algorithm. Model testing was performed on selected urban and rural areas. Additionally, a sensitivity analysis is conducted to analyze functionality. The model includes basic hydrological processes and is therefore less complex than fully physical models. The data needed to set up and run the new model include spatially and temporally distributed basic geometric and hydrologic variables (i.e., digital elevation model, precipitation, infiltration, and surface roughness). The model is implemented using open-source coding and can easily be applied to any selected area. Outputs are water volumes, depths, and velocities at different modeling times. Using GIS, results can be visualized and utilized for further analyses. The test, applied in urban as well as rural areas, demonstrates its user-friendliness, and that the estimated distributed water depths and water velocity at any time step can be saved and visualized.

  • 34.
    Nilsson, Kristina L.
    et al.
    Luleå tekniska universitet, Arkitektur och vatten.
    Lindberg, Johanna
    Luleå tekniska universitet, Medier ljudteknik och upplevelseproduktion och teater.
    Planering för klimatanpassning i sub-arktiska fjällområden2014Rapport (Annet vitenskapelig)
    Abstract [sv]

    Planering för klimatanpassning i sub-arktiska fjällområden är en rapport om en delstudie inom forskningsprojektet Klimatförändringar, klimatpåverkan och anpassning i Sub-Arktis, en fallstudie från norra Sveriges fjälltrakter, Climate change, impacts and adap-tation in the sub Arctic - A case study from the Northern Swedish mountains. De uppskattade framtida klimatförändringarna kommer att förändra inte bara vädret utan också landskapet i sub-arktiska områden. Detta kommer i sin tur att påverka markan-vändning och hur människor kan få sin utkomst i fjällområden. De viktigaste användarna, aktörerna och intressenterna av marken i dessa områden är samer, turistidkare, jägare, fiskare, naturvårdare m.fl. Dessutom används fjällområdena för friluftsliv, samt nationell och internationell turism. Denna rapport presenterar en delstudie inom det ämnesövergripande projektet, vilken fo-kuserar på markanvändningen successivt förändras och hur den kan anpassas till framtida klimatförändringar. Övriga delstudier i projektet har utvecklat modeller för detaljerade, nedskalade bedömningar av lokala data för klimat, vegetation, snöfördelning, biologisk mångfald och naturresurser. Dessa data ligger till grund för klimatanpassning av markan-vändningen. De samlade resultaten syftar till att användas för utveckling av lokala och regionala planeringsstrategier för olika nivåer av fysisk planering av markanvändning i sub-arktiska fjällområden. Det forskningsövergripande projektet, hade inledningsvis sin bas i Abisko naturve-tenskapliga station. Denna delstudie har genomförts på Luleå tekniska universitet av forskare inom arkitekturgruppen vid Institutionen för samhällsbyggnad och naturresurser. Det hanterar frågor om markanvändning och fysisk planering och omsätter undersök-ningsresultat från flera av de övriga delprojekten till faktorer att fungera som underlags-material eller aspekter att hantera i praktiskt tillämpade planeringssituationer.

  • 35. Piercey, Gerald
    et al.
    Ralph, Freeman
    Barrett, John
    Macneill, Andrew
    Jordaan, Ian
    Younan, Adel
    Fenz, Daniel
    Design of a Shipboard Local Load Measurement System to Collect Managed Ice Load Data2016Konferansepaper (Annet vitenskapelig)
    Abstract [en]

    Due to a lack of data, currently (and justifiably) conservative ice load assumptions are made in rig assessments allowing only very small floe sizes to contact non-Polar classed drilling rigs. In September 2015, in cooperation with the Norwegian University of Science and Technology (NTNU) and the Swedish Polar Research Secretariat (SPRS), ExxonMobil and C- CORE participated in the Oden Arctic Technology Research Cruise. A distinguishing aspect of this Cruise was: (a) performing ice management trials using two icebreakers, the Oden and the Frej; and (b) instrumenting the Frej, i.e. the secondary icebreaker and therefore collecting first-of-a-kind local ice load data during stationkeeping in managed ice. Unlike all prior data behind code pressure-area curves, which are based on transit in unmanaged ice and ship ramming, the new data are in managed ice field, representing true pressures and forces on a drilling or production vessel in a stationkeeping mode (moored, dynamically positioned (DP) or DP assist). This paper describes the design, installation and calibration of the Frej load measurement system. The system consists of an array of over 160 strain gauges installed over three panels on the bow and shoulder of the vessel. Prior to sailing, physical calibrations were performed as quality checks of the gauge installation and to benchmark finite element (FE) models used afterwards to convert measured strains into hull local ice pressures. More than 260 hours of local ice load data were collected throughout the program including measurements while stationkeeping in managed ice conditions in addition to actively managing ice and transit. The system remained operational through the entire field program without loss or damage to a single strain gauge. The data collected can contribute toward demonstrating the ability of existing rigs to resist some degree of managed ice, and hence can open the possibility for drilling season extension beyond open water, which can have a significant economic impact on arctic drilling. The resulting pressure-area curves will be the subject of a follow-up publication.

  • 36. Pustogvar, A.
    et al.
    Kulyakhtin, A.
    Sea ice density measurements. Methods and uncertainties2016Inngår i: Cold Regions Science and Technology, ISSN 0165-232X, E-ISSN 1872-7441, Vol. 131, s. 46-52Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Sea ice density is an important engineering and geophysical parameter. However, it lacks a standard method of measurement. In this paper, we show that the hydrostatic weighing method is the best available method that can capture the natural variation of the ice density throughout the ice thickness below the water line. The hydrostatic weighing method has a lower measurement uncertainty (0.2%) in comparison with the most common mass/volume method, which has an uncertainty of 4% when applied to ice samples with lengths and diameters of similar to 70 mm. The density of first-year level ice below the waterline measured by the hydrostatic weighing method in the present study lies in a range of 894-921 kg m(-3). The density of rafted multiyear ice and the ice above the waterline had a wider range, 863-929 kg m(-3). (C) 2016 Elsevier B.V. All rights reserved.

  • 37. Reese, Heather
    et al.
    Nyström, Mattias
    Nordkvist, Karin
    Olsson, Håkan
    Combining airborne laser scanning data and optical satellite data for classification of alpine vegetation2014Inngår i: International Journal of Applied Earth Observation and Geoinformation, ISSN 1569-8432, E-ISSN 1872-826X, Vol. 27, nr Part A, s. 81-90Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Climate change and outdated vegetation maps are among the reasons for renewed interest in mapping sensitive alpine and subalpine vegetation. Satellite data combined with elevation derivatives have been shown to be useful for mapping alpine vegetation, however, there is room for improvement. The inclusion of airborne laser scanning data metrics has not been widely investigated for alpine vegetation. This study has combined SPOT 5 satellite data, elevation derivatives, and laser data metrics for a 25km x 31km study area in Abisko, Sweden. Nine detailed vegetation classes defined by height, density and species composition in addition to snow/ice, water, and bare rock were classified using a supervised Random Forest classifier. Several of the classes consisted of shrub and grass species with a maximum height of 0.4m or less. Laser data metrics were calculated from the nDSM based on a 10m x 10m grid, and after variable selection, the metrics used in the classification were the 95th and 99th height percentiles, a vertical canopy density metric, the mean and standard deviation of height, a vegetation ratio based on the raw laser data point cloud with a variable height threshold (from 0.1 to 1.0m with 0.1m intervals), and standard deviation of these vegetation ratios. The satellite data used in classification was all SPOT bands plus NDVI and NDII, while the elevation derivatives consisted of elevation, slope and the Saga Wetness Index. Overall accuracy when using the combination of laser data metrics, elevation derivatives and SPOT 5 data increased by 6% as compared to classification of SPOT and elevation derivatives only, and increased by 14.2% compared to SPOT 5 data alone. The classes which benefitted most from inclusion of laser data metrics were mountain birch and alpine willow. The producer’s accuracy for willow increased from 18% (SPOT alone) to 41% (SPOT+elevation derivatives) and then to 55% (SPOT+elevation derivatives+laser data) when laser data were included, with the 95th height percentile and Saga Wetness Index contributing most to willow’s improved classification. Addition of laser data metrics did not increase the classification accuracy of spectrally similar dry heath (<0.3m height) and mesic heath (0.3-1.0m height), which may have been a result of laser data penetration of sparse shrub canopy or laser data processing choices. The final results show that laser data metrics combined with satellite data and elevation derivatives contributed overall to a better classification of alpine and subalpine vegetation.

  • 38. Rust, Lukas
    et al.
    Wehbe, Bilal
    Vyas, Shubham
    AUV Trajectory Optimization with hydrodynamic forces for icy moon exploration2023Inngår i: Proceedings of the 17th Symposium on Advanced Space Technologies in Robotics and Automation: ASTRA-2023, Scheltema, Leiden, The Netherlands, 2023Konferansepaper (Annet vitenskapelig)
    Abstract [en]

    To explore oceans on ice-covered moons in the solar system, energy-efficient Autonomous Underwater Vehicles (AUVs) with long ranges must cover enough distance to record and collect enough data. These usually underactuated vehicles are hard to control when performing tasks such as vertical docking or the inspection of vertical walls. This paper introduces a control strategy for DeepLeng to navigate in the ice-covered ocean of Jupiter&#8217;s moon Europa and presents simulation results preceding a discussion on what is further needed for robust control during the mission.

  • 39. Rydén, Jesper
    Statistical analysis of possible trends for extreme floods in northern Sweden2022Inngår i: River Research and Applications, ISSN 1535-1467, Vol. 38, nr 6, s. 1041-1050Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    With ongoing climate change, analysis of trends in maximum annual daily river flow is of interest. Flow magnitude and timing during the year were investigated in this study. Observations from 11 unregulated rivers in northern Sweden were analysed, using extreme-value distributions with time-dependent parameters. The Mann–Kendall test was used to investigate possible trends. The extreme-value statistics revealed no significant trends for the stations considered, but the Mann–Kendall test showed a significant upward trend for some stations. For timing of maximum flow (day of the year), the Mann–Kendall test revealed significant downward trends for two stations (with the longest records). This implies that the day of the maximum flow is occurring earlier in the year in northern Sweden.

  • 40. Shafrova, Svetlana
    et al.
    Holub, Curtis
    Harris, Matthew
    Cheng, Tao
    Matskevitch, Dmitri
    Foltz, Raymond
    Mitchell, Douglas
    Common Operational Picture COP Requirements for Floating Drilling in Pack Ice2016Konferansepaper (Annet vitenskapelig)
    Abstract [en]

    A Common Operational Picture (COP) can generally be described as a system of hardware and software that produces a shared display of information to facilitate situational awareness and decision making. A brief history of the development and use of COP technology in Arctic operations is provided. Experience and learnings from ExxonMobil's research into the use of COPs in ice management and Arctic floating drilling is described. Experience gained from simulations, desktop studies, and field observations is used to frame preliminary functional requirements for such technology needed for future Arctic floating drilling operations in high concentration ice. The COP must facilitate the planning and execution of complex and remote operations with many geographically distributed assets (e.g., drilling rig; icebreakers; shore base; manned or unmanned aviation) and stakeholders (e.g., icebreaker captains, drilling management, ice analysts, weather forecasters) at times communicating over limited bandwidth channels. The COP will serve to collect, store, communicate, and display the necessary data and information. The role of COP components (e.g., databases; communication network, displays) is described and functional requirements are outlined.

  • 41.
    Shafrova, Svetlana
    et al.
    ExxonMobil Upstream Research Company, Spring, TX.
    Matskevitch, Dmitri
    ExxonMobil Upstream Research Company, Spring, TX.
    Holub, Curtis
    ExxonMobil Upstream Research Company, Spring, TX.
    Kokkinis, Ted
    ExxonMobil Upstream Research Company, Spring, TX.
    Identification of Potentially Unmanageable Ice Features2017Inngår i: International Conference on Ocean, Offshore and Arctic Engineering: Volume 8: Polar and Arctic Sciences and Technology; Petroleum Technology, 2017, Vol. 8Konferansepaper (Annet vitenskapelig)
    Abstract [en]

    Satellite remote sensing technology plays an important role in ice monitoring and characterization in support of ice management operations for Arctic floating drilling that previously have been described by industry to include three stages: (1) far-field reconnaissance for potentially unmanageable ice features (2) mid-field verification of ice breakability and (3) near-field ice floe size reduction.

    The paper discusses the application of satellite remote sensing methods for identification of Potentially Unmanageable Ice Features (PUIF) as well as challenges associated with satellite data interpretation and feature tracking. Examples of PUIF identification using both publicly and commercially available satellite imagery and other remote sensing data collected during the Oden Arctic Technology Research Cruise 2015 (OATRC 2015) are presented and the challenges with the PUIF detection and monitoring are discussed.

    In addition, airborne remote sensing systems for PUIF identification, both existing (such as Electromagnetic Induction (EMI)) and under development (such as dual frequency radar, multi-band synthetic aperture radar), are discussed and their capabilities contrasted and compared to satellite-based methods. Furthermore, potential ways of optimally combining airborne and satellite remote sensing are proposed.

  • 42.
    Siegel, Karolina
    et al.
    Stockholms universitet, Institutionen för miljövetenskap.
    Neuberger, Almuth
    Stockholms universitet, Institutionen för miljövetenskap.
    Karlsson, Linn
    Stockholms universitet, Institutionen för miljövetenskap.
    Zieger, Paul
    Stockholms universitet, Institutionen för miljövetenskap.
    Mattsson, Fredrik
    Stockholms universitet, Institutionen för miljövetenskap.
    Duplessis, Patrick
    Dada, Lubna
    Daellenbach, Kaspar
    Schmale, Julia
    Baccarini, Andrea
    Krejci, Radovan
    Stockholms universitet, Institutionen för miljövetenskap.
    Svenningsson, Birgitta
    Chang, Rachel
    Ekman, Annica M. L.
    Stockholms universitet, Meteorologiska institutionen (MISU).
    Riipinen, Ilona
    Stockholms universitet, Institutionen för miljövetenskap.
    Mohr, Claudia
    Stockholms universitet, Institutionen för miljövetenskap.
    Using Novel Molecular-Level Chemical Composition Observations of High Arctic Organic Aerosol for Predictions of Cloud Condensation Nuclei2022Inngår i: Environmental Science and Technology, ISSN 0013-936X, E-ISSN 1520-5851, Vol. 56, nr 19, s. 13888-13899Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Predictions of cloud droplet activation in the late summertime (September) central Arctic Ocean are made using κ-Köhler theory with novel observations of the aerosol chemical composition from a high-resolution time-of-flight chemical ionization mass spectrometer with a filter inlet for gases and aerosols (FIGAERO-CIMS) and an aerosol mass spectrometer (AMS), deployed during the Arctic Ocean 2018 expedition onboard the Swedish icebreaker Oden. We find that the hygroscopicity parameter κ of the total aerosol is 0.39 ± 0.19 (mean ± std). The predicted activation diameter of ∼25 to 130 nm particles is overestimated by 5%, leading to an underestimation of the cloud condensation nuclei (CCN) number concentration by 4-8%. From this, we conclude that the aerosol in the High Arctic late summer is acidic and therefore highly cloud active, with a substantial CCN contribution from Aitken mode particles. Variability in the predicted activation diameter is addressed mainly as a result of uncertainties in the aerosol size distribution measurements. The organic κ was on average 0.13, close to the commonly assumed κ of 0.1, and therefore did not significantly influence the predictions. These conclusions are supported by laboratory experiments of the activation potential of seven organic compounds selected as representative of the measured aerosol.

  • 43. Sinitsyn, Anatoly
    et al.
    Sinitsyna, Taisiya
    Hendrikse, Hayo
    Ice Station for Ramming Test on OATRC 20132016Inngår i: Proceedings of the 23rd IAHR International Symposium on Ice, 2016Konferansepaper (Annet vitenskapelig)
    Abstract [en]

    In August 2013 the Oden Arctic Technology Research Cruise (OATRC2013) was undertaken in the Fram Strait, North-East Greenland. A ramming test by the icebreaker was one of the research tasks. The test was performed on an ice flow which included a large ice ridge, and a region of level ice spreading behind the ice ridge for several hundred meters. An ice station was established for data collection on the physical and mechanical properties of the ice ridge and level ice. Ice thickness, crystal structure, salinity, temperature, density, and uniaxial compressive strength were obtained for the level ice, and the morphology of the ice ridge was studied. Moreover, the accuracy of a prototype electromagnetic antenna EM-34 ICE was examined through the measurement of ice thickness on the ice station. The applicability of the electromagnetic antenna in proximity of the icebreaker (as in the vicinity of a massive metal body) was studied in particular. Some results of the fieldwork and workflow are presented and discussed. Data on ice properties can be useful for assessment of ice conditions and analysis of the ramming test, while description of the workflow can be used for planning of field operations.

  • 44. Stratmann, Tanja
    Deciphering the DOC composition in the Arctic Ocean using parallel factor analysis2019Independent thesis Advanced level (degree of Master (Two Years))Oppgave
    Abstract [en]

    Parallel factor analysis (PARAFAC) is a decomposition method that can decompose multilinear data into unique components consisting of loading vectors and score vectors. Here, it was used to decompose trilinear excitation-emission matrices of fluorescing dissolved organic matter (FDOM) into individual components. Maxima of excitation and emission loadings of individual components can be determined and used to identify the broad chemical composition of FDOM and its origin based on published literature. This study investigated the spectral properties of colored dissolved organic matter (CDOM) and FDOM from the central Arctic Ocean. I assessed which fluorescent components could be identified using PARAFAC and I examined the vertical distribution of CDOM and FDOM characteristics in the central Arctic Ocean. Absorption coefficient at 375 nm (a375) had an average value of (mean±SE) 0.37±2.08×10-2 m-1. The ratio between the absorption coefficients at 250 nm and 365 nm, E2:E3, was on average 13.7±0.84, and the spectral slope coefficient between 275 and 295 nm, S275-295, was22.5±0.65 µm-1. a375 and E2:E3 were highest in surface waters and decreased with depth in the form of a power function, whereas S275-295 increased with depth. Based on the relationship ofa375 vs. the spectral slope coefficient between 300 and 650 nm, S300-650, CDOM was classified as being of terrestrial origin. The absorption coefficient at 300 nm was used to differentiate between freshly-produced semi-labile CDOM and refractory CDOM. Semi-labile CDOM was detected down to a water depth of 1,500 m. A PARAFAC model for three components could be validated and explained 99.0% of the data variability. Fluorescent component FC1 had an excitation loading maximum at <240 nm and an emission loading maximum between 412 and 416 nm. Based on these maxima, the component could be identified as a terrestrial, humic-like component that is characteristic for forest streams and wetlands. The second fluorescent component FC2 had an excitation loading maximum at 255 nm and a maximum emission loading at 454 nm. It was again identified as a terrestrial, humic-like component from forest streams and wetlands and is a degradation product of humic substances. The third fluorescent component that was identified with PARAFAC had an excitation loading maximum at 280 m and an emission loading maximum at 340 nm. It has similar spectral properties like the classical peak T and could be tryptophan-/ protein like. When the information about CDOM and FDOM were combined in a principal component analysis, loadings of the three absorption coefficients at 300 nm, 350 nm, and 375 nm were positively correlated with principal component 1, whereas loadings of the spectral slope coefficient 2S275-295 and the maximum fluorescence intensity of FDOM component FC2 were positively correlated with principal component 2. As the scores of surface water masses clustered around the loadings of the absorption coefficients, principal component 1 might represent the terrestrial derived, freshly-produced CDOM in surface waters. The fluorescence intensity of FC 1 decreased with depth, whereas the fluorescence intensity ofFC2 was relatively stable, but highest in deep waters. This suggests that terrestrial-humic likeFC1 is more and more degraded with increasing water depth and its degradation product FC2accumulates in deep waters. The fluorescence intensity of tryptophan-like/ protein-like FC3 had a maximum fluorescence intensity in intermediate waters (~150–2,000 m) and this component was likely released during a phytoplankton bloom. This study shows that CDOM and FDOM properties have a vertical distribution in the central Arctic Ocean and can be used to distinguish between surface water and the water masses below. 

  • 45. Sudakow, I.
    et al.
    Asari, V. K.
    Liu, R.
    Demchev, D.
    MeltPondNet: A Swin Transformer U-Net for Detection of Melt Ponds on Arctic Sea Ice2022Inngår i: IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing, ISSN 1939-1404, E-ISSN 2151-1535, Vol. 15, s. 8776-8784Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    High-resolution aerial photographs of Arctic region are a great source for different sea ice feature recognition, which are crucial to validate, tune, and improve climate models. Melt ponds on the surface of melting Arctic sea ice are of particular interest as they are sensitive and valuable indicators and are proxy to the processes in the Arctic climate system. Manual analysis of this remote sensing data is extremely difficult and time-consuming due to the complex shapes and unpredictable boundaries of the melt ponds, and that leads to the necessity for automatizing the processes. In this study, we propose a robust and efficient automatic method for melt pond region segmentation and boundary extraction from high-resolution aerial photographs. The proposed algorithm is based on a swin transformer U-Net in which we introduce novel cross-channel attention mechanisms into the decoder design. The framework operates with optical data and allows for classifying imagery into four classes, i.e., sea ice/snow, open water, melt pond, and submerged ice. We use aerial photographs collected during the Healy–Oden Trans Arctic Expedition over Arctic sea ice in the summer season of 2005 as test data. The experimental results show that the proposed method is suitable for precise automatic extraction of melt pond geometry, and it can also be extended for other optical data sources that involve melt ponds. The approach has a promising potential to be used to analyze melt ponds' corresponding changes between years.

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