AWI ICETrack - Antarctic and Arctic Sea Ice Monitoring and Tracking Tool (Vers. 1.1)

Purpose of this document is the documentation of the ICETrack application developed at the Alfred Wegener Institute for Polar and Marine Research. This document will give a short description of the routines and methods applied to monitor key areas and calculate sea ice trajectories using sea ice motion and concentration data from satellites and additional parameters extracted along pathways of sea ice. Some of the results of the ICETrack application are publically available for download and a technical description of the data format is given here

Improvement and Sensitivity Analysis of Thermal Thin-Ice Thickness Retrievals

Considering the sea ice decline in the Arctic during the last decades, polynyas are of high research interest since these features are core areas of new ice formation. The determination of ice formation requires accurate retrieval of polynya area and thin-ice thickness (TIT) distribution within the polynya. We use an established energy balance model to derive TITs with MODIS ice surface temperatures $(T_{s})$ and NCEP/DOE Reanalysis II in the Laptev Sea for two winter seasons. Improvements of the algorithm mainly concern the implementation of an iterative approach to calculate the atmospheric flux components taking the atmospheric stratification into account. Furthermore, a sensitivity study is performed to analyze the errors of the ice thickness. The results are the following: 1) 2-m air temperatures $(T_{a})$ and $T_{s}$ have the highest impact on the retrieved ice thickness; 2) an overestimation of $T_{a}$ yields smaller ice thickness errors as an underestimation of $T_{a}$; 3) NCEP $T_{a}$ shows often a warm bias; and 4) the mean absolute error for ice thicknesses up to 20 cm is $pm$4.7 cm. Based on these results, we conclude that, despite the shortcomings of the NCEP data (coarse spatial resolution and no polynyas), this data set is appropriate in combination with MODIS $T_{s}$ for the retrieval of TITs up to 20 cm in the Laptev Sea region. The TIT algorithm can be applied to other polynya regions and to past and future time periods. Our TIT product is a valuable data set for verification of other model and remote sensing ice thickness data

Investigation of ice formation and water mass modification in eastern Laptev Sea polynyas by means of satellites and models

Salt expelled during the formation of ice in polynyas leads to a downward precipitation of brine that causes thermohaline convection and erodes the density stratification of the water column. In this thesis we investigate by means of flux models and satellite data the ability of the Western New Siberian (WNS) flaw polynya to modify the stratification of the water column and to form saline bottom water. The accuracy of existent microwave satellite-based polynya monitoring methods is assessed by a comparison of derived estimates with airborne electromagnetic ice thickness measurements and aerial photographs taken across the polynya. The cross-validation indicates that in the narrow flaw polynyas of the Laptev Sea the coarse resolution of commonly used microwave channel combinations provokes errors through mixed signals at the fast and pack ice edges. Likewise, the accuracy of flux models is tested by comparing model results to ice thickness and ice production estimates derived from high-resolution thermal infrared satellite observations. We find that if a realistic fast ice boundary and parameterization of the collection depth H is used and if the movement of the pack ice edge is prescribed correctly, the model is an appropriate tool for studying polynya dynamics and estimating associated fluxes. Hence, a flux model is used to examine the effect of ice production on the stratification of the water column. The ability of the polynya to form dense shelf bottom water is investigated by adding the brine released during an except ionally strong WNS polynya event in 2004 to the average winter density stratification of the water body. Owing to the strong density stratification and the apparent lack of extreme polynya events in the eastern Laptev Sea, we find the likelihood of convective mixing down to the bottom to be extremely low. We conclude that the recently observed breakdown of the stratification during polynya events is therefore predominantly related to wind- and tidally-driven turbulent mixing

Campaign Report TIFAX 2016: Sea ice thickness measurements from Station Nord, Greenland

During the last decade, an increased advection of thick multi-year ice that originates from an area north of Greenland, out of the Arctic through the Fram Strait has been observed. A replacement of this old and thick sea ice by much thinner ice might precondition for rapid sea ice retreat in summer. Aim of the TIFAX campaign is therefore to monitor ice conditions during summer in the main export pathway of the Arctic Ocean. The campaign complements the large scale spring sea ice survey PAMARCMIP and is a continuation of earlier TIFAX campaign in 2010, 2011, 2012 and 2015

Winter sea ice export from the Laptev Sea preconditions the local summer sea ice cover and fast ice decay

Ice retreat in the eastern Eurasian Arctic is a consequence of atmospheric and oceanic processes and regional feedback mechanisms acting on the ice cover, both in winter and summer. A correct representation of these processes in numerical models is important, since it will improve predictions of sea ice anomalies along the Northeast Passage and beyond. In this study, we highlight the importance of winter ice dynamics for local summer sea ice anomalies in thickness, volume and extent. By means of airborne sea ice thickness surveys made over pack ice areas in the south-eastern Laptev Sea, we show that years of offshore-directed sea ice transport have a thinning effect on the late-winter sea ice cover. To confirm the preconditioning effect of enhanced offshore advection in late winter on the summer sea ice cover, we perform a sensitivity study using a numerical model. Results verify that the preconditioning effect plays a bigger role for the regional ice extent. Furthermore, they indicate an increase in volume export from the Laptev Sea as a consequence of enhanced offshore advection, which has far-reaching consequences for the entire Arctic sea ice mass balance. Moreover we show that ice dynamics in winter not only preconditions local summer ice extent, but also accelerate fast-ice decay

Evaluierung satelliten- und modellgestützter Eisinformationen zur Unterstützung des Forschungseisbrechers Polarstern

Ziel dieser Arbeit ist, die auf dem Forschungseisbrecher Polarstern verfügbaren Modell- und Satellitendaten hinsichtlich ihrer Anwendbarkeit als Grundlage für nautische Entscheidungsfindungsprozesse zur Planung und Durchführung von Einsätzen im Packeis zu beurteilen. Die Daten stammen von verschiedenen Providern und werden über das bordeigene ECS System (das IceGIS) automatisch übermittelt. In dieser Arbeit werden zunächst die verfügbaren Datenprodukte beschrieben und im Weiteren deren potenzielle Anwendung zur Planung und Durchführung von Einsätzen in eisbedeckten Gewässern aufgeführt. Die Analyse setzt sich kritisch mit den gegebenen Unsicherheiten und Einschränkungen der jeweiligen Datenprodukte auseinander und zeigt so die Grenzen der Anwendbarkeit auf

TIFAX 2017 Campaign Report: Sea ice thickness measurements with Polar 6 from Station Nord and Alert

Arctic sea ice extent and thickness have undergone dramatic changes in the past decades: Summer sea ice extent has declined at an annual rate of approximately 12.7 % per decade over the satellite record (1978 – present, Meier et al., 2014) and its mean thickness has decreased by 0.58 m +/- 0.07 m per decade over the period 2000 - 2012 (Lindsay et al., 2015). The thinning of sea ice is accompanied by an increase of ice drift velocity (Spreen et al., 2011), deformation (Rampal et al., 2009) and a decrease of net ice growth rates. Climate model simulations indicate that ice extent and thickness will further decline through the 21st century in response to atmospheric greenhouse gas increases (Vravus et al., 2012). However, the mass balance of Arctic sea ice is not only determined by changes in the energy balance of the coupled ice-ocean-atmosphere system but also by the increasing influence of dynamic effects. One aspect of the mass balance of Arctic sea ice are changes of ice volume export rates through Fram Strait and the decline of thick and old multi-year ice North of Ellesmere Island. Thickness surveys carried out North of Greenland and Fram Strait give insight into composition and properties of Arctic sea ice in general and how it changes over time. An extensive data set of ground-based and airborne electromagnetic ice thickness measurements were collected between 2001 and 2016 during several aircraft (PAMARCMIP, TIFAX) and Polarstern campaigns. The first aim of the TIFAX 2017 campaign is to complement earlier measurements made north of Svalbard, Greenland and in Fram Strait. Sea ice thickness information will be used to examine the connection between thickness variability, ice age and source area. Together with satellite based information on sea ice motion, data will be used to number sea ice outflow through Fram Strait in summer. These estimates shall improve the understanding of interannual variability in summer sea ice outflow and complement existing winter volume flux calculations. A second objective is to extent sea ice thickness measurements to the Lincoln Sea where we will study thinning of sea ice due to reduction of old multi-year ice in this area. Like the measurements planned over Fram Strait area, the surveys are a continuation of earlier aircraft campaigns made North of Alert and shall improve understanding of ice mass balance changes in the Arctic. In addition to measurements over sea ice, laser scanner flights over glaciers were made within the framework of MABANG

Data report: EM-Bird ice thickness measurements in the Laptev Sea in April 2012 and 2008

The two campaigns were carried out within the framework of the Russian-German research cooperation 'Laptev Sea System'. Measurements were made in the southeastern Laptev Sea at the end of April 2008 (campaign Transdrift (TD) XIII) and 2012 (campaign TD XX). Data obtained over pack ice zones north of the landfast ice edge were used to estimate sea ice production in flaw polynyas (Rabenstein et al. 2013, Krumpen et al. 2011) and for validation of ESA's SMOS (Soil Moisture Ocean Salinity) satellite derived ice thickness products. Flaw polynyas are open water sites between pack ice and fast ice of high net ice production sustained by winds

Sea ice mass balance buoys during MOSAiC in the context of long-term buoy data in the Transpolar Drift system

Presentation of SIMBA buoy ice & snow thickness retrievals (first preliminary version for Arctic PASSION) in relation to the MOSAiC drift experiment in 2019/2020. Part of the session on "MOSAiC Observations in the Context of Historical Data" during the 2nd MOSAiC Science conference in Boulder, Colorado, US (February 13-17, 2023)

Moment-Based Order-Independent Transparency

Compositing transparent surfaces rendered in an arbitrary order requires techniques for order-independent transparency. Each surface color needs to be multiplied by the appropriate transmittance to the eye to incorporate occlusion. Building upon moment shadow mapping, we present a moment-based method for compact storage and fast reconstruction of this depth-dependent function per pixel. We work with the logarithm of the transmittance such that the function may be accumulated additively rather than multiplicatively. Then an additive rendering pass for all transparent surfaces yields moments. Moment-based reconstruction algorithms provide approximations to the original function, which are used for compositing in a second additive pass. We utilize existing algorithms with four or six power moments and develop new algorithms using eight power moments or up to four trigonometric moments. The resulting techniques are completely order-independent, work well for participating media as well as transparent surfaces and come in many variants providing different tradeoffs. We also utilize the same approach for the closely related problem of computing shadows for transparent surfaces