scholarly journals Regional Assessments of Surface Ice Elevations from Swath-Processed CryoSat-2 SARIn Data

2021 ◽  
Vol 13 (11) ◽  
pp. 2213
Author(s):  
Natalia Havelund Andersen ◽  
Sebastian Bjerregaard Simonsen ◽  
Mai Winstrup ◽  
Johan Nilsson ◽  
Louise Sandberg Sørensen
Keyword(s):  
Radar Data ◽  
The Arctic ◽  
Validation Data ◽  
Sea Levels ◽  
Ice Surface ◽  
Spatial Coverage ◽  
Elevation Data ◽  
The Stability ◽  
Surface Ice ◽  
The Cost

The Arctic responds rapidly to climate change, and the melting of land ice is a major contributor to the observed present-day sea-level rise. The coastal regions of these ice-covered areas are showing the most dramatic changes in the form of widespread thinning. Therefore, it is vital to improve the monitoring of these areas to help us better understand their contribution to present-day sea levels. In this study, we derive ice-surface elevations from the swath processing of CryoSat-2 SARIn data, and evaluate the results in several Arctic regions. In contrast to the conventional retracking of radar data, swath processing greatly enhances spatial coverage as it uses the majority of information in the radar waveform to create a swath of elevation measurements. However, detailed validation procedures for swath-processed data are important to assess the performance of the method. Therefore, a range of validation activities were carried out to evaluate the performance of the swath processor in four different regions in the Arctic. We assessed accuracy by investigating both intramission crossover elevation differences, and comparisons to independent elevation data. The validation data consisted of both air- and spaceborne laser altimetry, and airborne X-band radar data. There were varying elevation biases between CryoSat-2 and the validation datasets. The best agreement was found for CryoSat-2 and ICESat-2 over the Helheim region in June 2019. To test the stability of the swath processor, we applied two different coherence thresholds. The number of data points was increased by approximately 25% when decreasing the coherence threshold in the processor from 0.8 to 0.6. However, depending on the region, this came with the cost of an increase of 33–65% in standard deviation of the intramission differences. Our study highlights the importance of selecting an appropriate coherence threshold for the swath processor. Coherence threshold should be chosen on a case-specific basis depending on the need for enhanced spatial coverage or accuracy.

scholarly journals Bed topography of Jakobshavn Isbræ, Greenland, and Byrd Glacier, Antarctica

2014 ◽  
Vol 60 (223) ◽  
pp. 813-833 ◽  
Author(s):  
S. Gogineni ◽  
J.-B. Yan ◽  
J. Paden ◽  
C. Leuschen ◽  
J. Li ◽  
...  
Keyword(s):  
High Sensitivity ◽  
Radar Data ◽  
Unmanned Aerial Systems ◽  
Music Algorithm ◽  
Bed Topography ◽  
Ice Surface ◽  
Elevation Data ◽  
Track Surface ◽  
Cross Track ◽  
Aerial Systems

AbstractThis paper presents the bed topography of Jakobshavn Isbræ, Greenland, and Byrd Glacier, Antarctica, derived from sounding these glaciers with high-sensitivity radars. To understand the processes causing the speed-up and retreat of outlet glaciers, and to enable the development of next-generation ice-sheet models, we need information on bed topography and basal conditions. To this end, we performed measurements with the progressively improved Multichannel Coherent Radar Depth Sounder/Imager (MCoRDS/I). We processed the data from each antenna-array element using synthetic aperture radar algorithms to improve radar sensitivity and reduce along-track surface clutter. We then applied array and image-processing algorithms to extract the weak bed echoes buried in off-vertical scatter (cross-track surface clutter). At Jakobshavn Isbræ, we observed 2.7 km thick ice ~30 km upstream of the calving front and ~850 m thick ice at the calving front. We also observed echoes from multiple interfaces near the bed. We applied the MUSIC algorithm to the data to derive the direction of arrival of the signals. This analysis revealed that clutter is dominated by the ice surface at Jakobshavn Isbræ. At Byrd Glacier, we found ~3.62 km thick ice, as well as a subglacial trench ~3.05 km below sea level. We used ice thickness information derived from radar data in conjunction with surface elevation data to generate bed maps for these two critical glaciers. The performance of current radars must be improved further by ~15 dB to fully sound the deepest part of Byrd Glacier. Unmanned aerial systems equipped with radars that can be flown over lines spaced as close as 5 m apart in the cross-track direction to synthesize a two-dimensional aperture would be ideal for collecting fine-resolution data over glaciers like Jakobshavn near their grounding lines.

scholarly journals Airborne ultra-wideband radar sounding over the shear margins and along flow lines at the onset region of the Northeast Greenland Ice Stream

2021 ◽  
Author(s):  
Steven Franke ◽  
Daniela Jansen ◽  
Tobias Binder ◽  
John D. Paden ◽  
Nils Dörr ◽  
...  
Keyword(s):  
High Resolution ◽  
Ice Core ◽  
Radar Data ◽  
Ultra Wideband ◽  
Flow Lines ◽  
Data Set ◽  
Ice Surface ◽  
Ice Stream ◽  
Spatial Coverage ◽  
Wideband Radar

Abstract. We present a high-resolution airborne radar data set (EGRIP-NOR-2018) for the onset region of the Northeast Greenland Ice Stream (NEGIS). The radar data were acquired in May 2018 with Alfred Wegener Institute’s multichannel ultra-wideband (UWB) radar mounted on the Polar6 aircraft. Radar profiles cover an area of ~24000 km2 and extend over the well-defined shear margins of the NEGIS. The survey area is centred at the location of the drill site of the East Greenland Ice-Core Project (EastGRIP) and several radar lines intersect at this location. The survey layout was designed to: (i) map the stratigraphic signature of the shear margins with radar profiles aligned perpendicular to ice flow, (ii) trace the radar stratigraphy along several flow lines and (iii) provide spatial coverage of ice thickness and basal properties. While we are able to resolve radar reflections in the deep stratigraphy, we can not fully resolve the steeply inclined reflections at the tightly folded shear margins in the lower part of the ice column. The NEGIS is causing the most significant discrepancies between numerically modelled and observed ice surface velocities. Given the high likelihood of future climate and ocean warming, this extensive data set of new high-resolution radar data in combination with the EastGRIP ice core will be a key contribution to understand the past and future dynamics of the NEGIS. The EGRIP-NOR-2018 radar data products can be obtained at the PANGAEA Data Publisher (https://doi.pangaea.de/10.1594/PANGAEA.928569; Franke et al. 2021a).

scholarly journals Validation of swath processed Cryosat-2 SARin data with different validation datasets at four different locations.

2021 ◽  
Author(s):  
Natalia Havelund ◽  
Louise Sørensen ◽  
Sebastian Simonsen
Keyword(s):  
Sea Level Rise ◽  
Sea Level ◽  
Signal To Noise Ratio ◽  
Laser Scanner ◽  
Radar Data ◽  
Validation Data ◽  
Ice Caps ◽  
Ice Cap ◽  
Ice Surface ◽  
Global Sea Level

<p>Monitoring the Ice Sheets and ice caps in the polar region is important in a changing climate, and especially the coastal regions, which is the area that is most sensitive to changes in the climate and contributes to the global sea level rise (Gardner et al., 2013).</p><p>In this study, swath processed CryoSat-2 ice surface elevations are validated at four different locations with four different types of validation datasets; The Petermann Glacier and Nioghalvfjerdsfjorden Glacier in Northern Greenland, the Helheim glacier in the Eastern Greenland, and the ice cap of Austfonna located in Svalbard. The validation data consist of X-band radar data, Operation ICEBridge, ICESat-2 laser data, and Airborne Laser Scanner data respectively.</p><p>Swath processing improves the radar data coverage compared to conventional retracking, though, the extra amount of data leads to lower signal-to-noise ratio (Foresta et al., 2018), making validation of the swath processed data immensely important. Using different validation datasets allow us to investigate how the validation is impacted by the different platforms’ ability to measure the surface topography.</p><p> </p><p><strong>Bibliography:</strong></p><p>Foresta L, Gourmelen N, Weissgerber F, Nienow P, Shepherd A and Drinkwater M (2018) Heterogeneous and rapid ice loss over the Patagonian Ice Fields 2 revealed by CryoSat-2 swath radar altimetry. Remote Sensing of Environment, (minorrev(March), 0–1, ISSN 00344257 (doi: 10.1016/j.rse.2018.03.041)</p><p> </p><p>Gardner AS, Moholdt G, Cogley JG, Wouters B, Arendt AA, Wahr J, Berthier E, Hock R, Pfeffer WT, Kaser G, Ligtenberg SRM, Bolch T, Sharp MJ, Hagen JO, van den Broeke MR and Paul F (2013) A Reconciled Estimate of Glacier Contributions to Sea Level Rise: 2003 to 2009. Science, 340(6134), 852–857, ISSN 0036-8075 (doi: 10.1126/science.1234532)</p><p> </p><p> </p>

Direction Finding and Likelihood Ratio Detection for Oceanographic HF Radars

2021 ◽  
Author(s):  
Anthony Kirincich ◽  
Libe Washburn
Keyword(s):  
Likelihood Ratio ◽  
Correlation Coefficients ◽  
Likelihood Estimation ◽  
Radar Data ◽  
Hf Radar ◽  
Estimation Methods ◽  
Spatial Coverage ◽  
Similar Accuracy ◽  
The Cost ◽  
Improved Accuracy

Abstract Previous work with simulations of oceanographic HF radars has identified possible improvements when using Maximum Likelihood Estimation (MLE) for directional-of-arrival (DOA), however methods for determining the number of emitters (here defined as spatially distinct patches of the ocean surface) have not realized these improvements. Here we describe and evaluate the use of the Likelihood Ratio (LR) for emitter detection, demonstrating its application to oceanographic HF radar data. The combined detection-estimation methods MLE-LR are compared with MUSIC and MUSIC parameters for SeaSonde HF radars, along with a method developed for 8-channel systems known as MUSIC-Highest. Results show that the use of MLE-LR produces similar accuracy in terms of the RMS difference and correlation coefficients squared, as previous methods. We demonstrate that improved accuracy can be obtained for both methods, at the cost of fewer velocity observations and decreased spatial coverage. For SeaSondes, accuracy improvements are obtained with less commonly used parameter sets. The MLE-LR is shown to be able to resolve simultaneous closely spaced emitters, which has the potential to improve observations obtained by HF radars operating in complex current environments.

The features of land development and construction in the Arctic region, taking into account the dynamics of climatic changes

2021 ◽  
pp. 425-431
Author(s):  
G.I. Bykova ◽  
M.A. Grippas
Keyword(s):  
Climate Change ◽  
Land Development ◽  
Arctic Region ◽  
Coastal Areas ◽  
The Arctic ◽  
Arctic Seas ◽  
Sea Levels ◽  
Rising Sea Levels ◽  
The Cost ◽  
The Arctic Region

The article reflects the specifics of land development and construction in the Arctic North. It is necessary to use climate information effectively to select the best solutions and to avoid undue overestimation of the cost of facilities, increased heat loss, low heat resistance and strength affecting overspending. Recent trends in the context of dynamic climate change leading to rising sea levels, and possible flooding of coastal areas of the Arctic Seas are considered in this paper. The authors underline a great danger to infrastructure in result of possible destruction of coastal areas. English version of the article is available at URL: https://panor.ru/articles/peculiarities-of-land-development-and-construction-in-the-arctic-region-given-the-dynamics-of-climate-change/64263.html

scholarly journals Black Hole Algorithm for Sustainable Design of Counterfort Retaining Walls

2020 ◽  
Vol 12 (7) ◽  
pp. 2767 ◽  
Author(s):  
Víctor Yepes ◽  
José V. Martí ◽  
José García
Keyword(s):  
Black Hole ◽  
Sustainable Design ◽  
Retaining Walls ◽  
The Other ◽  
Trade Off ◽  
Construction Company ◽  
Geometric Variables ◽  
The Stability ◽  
The Cost ◽  
Black Hole Algorithm

The optimization of the cost and CO 2 emissions in earth-retaining walls is of relevance, since these structures are often used in civil engineering. The optimization of costs is essential for the competitiveness of the construction company, and the optimization of emissions is relevant in the environmental impact of construction. To address the optimization, black hole metaheuristics were used, along with a discretization mechanism based on min–max normalization. The stability of the algorithm was evaluated with respect to the solutions obtained; the steel and concrete values obtained in both optimizations were analyzed. Additionally, the geometric variables of the structure were compared. Finally, the results obtained were compared with another algorithm that solved the problem. The results show that there is a trade-off between the use of steel and concrete. The solutions that minimize CO 2 emissions prefer the use of concrete instead of those that optimize the cost. On the other hand, when comparing the geometric variables, it is seen that most remain similar in both optimizations except for the distance between buttresses. When comparing with another algorithm, the results show a good performance in optimization using the black hole algorithm.

scholarly journals Gap Filling of the CALYPSO HF Radar Sea Surface Current Data through Past Measurements and Satellite Wind Observations

2016 ◽  
Vol 2016 ◽  
pp. 1-9 ◽  
Author(s):  
Adam Gauci ◽  
Aldo Drago ◽  
John Abela
Keyword(s):  
Oil Spills ◽  
Surface Current ◽  
Radar Data ◽  
Current Data ◽  
Hf Radar ◽  
Sea Surface ◽  
Machine Learning Techniques ◽  
Learning Techniques ◽  
Spatial Coverage ◽  
Essential Components

High frequency (HF) radar installations are becoming essential components of operational real-time marine monitoring systems. The underlying technology is being further enhanced to fully exploit the potential of mapping sea surface currents and wave fields over wide areas with high spatial and temporal resolution, even in adverse meteo-marine conditions. Data applications are opening to many different sectors, reaching out beyond research and monitoring, targeting downstream services in support to key national and regional stakeholders. In the CALYPSO project, the HF radar system composed of CODAR SeaSonde stations installed in the Malta Channel is specifically serving to assist in the response against marine oil spills and to support search and rescue at sea. One key drawback concerns the sporadic inconsistency in the spatial coverage of radar data which is dictated by the sea state as well as by interference from unknown sources that may be competing with transmissions in the same frequency band. This work investigates the use of Machine Learning techniques to fill in missing data in a high resolution grid. Past radar data and wind vectors obtained from satellites are used to predict missing information and provide a more consistent dataset.

scholarly journals Longevity of Raw and Lyophilized Crude Urease Extracts

2021 ◽  
Vol 2 (2) ◽  
pp. 325-334
Author(s):  
Neda Javadi ◽  
Hamed Khodadadi Tirkolaei ◽  
Nasser Hamdan ◽  
Edward Kavazanjian
Keyword(s):  
Crude Extract ◽  
Room Temperature ◽  
Low Cost ◽  
Extraction Process ◽  
Crude Extracts ◽  
Simple Extraction ◽  
Commercial Applications ◽  
Stable Source ◽  
The Stability ◽  
The Cost

The stability (longevity of activity) of three crude urease extracts was evaluated in a laboratory study as part of an effort to reduce the cost of urease for applications that do not require high purity enzyme. A low-cost, stable source of urease will greatly facilitate engineering applications of urease such as biocementation of soil. Inexpensive crude extracts of urease have been shown to be effective at hydrolyzing urea for carbonate precipitation. However, some studies have suggested that the activity of a crude extract may decrease with time, limiting the potential for its mass production for commercial applications. The stability of crude urease extracts shown to be effective for biocementation was studied. The crude extracts were obtained from jack beans via a simple extraction process, stored at room temperature and at 4 ℃, and periodically tested to evaluate their stability. To facilitate storage and transportation of the extracted enzyme, the longevity of the enzyme following freeze drying (lyophilization) to reduce the crude extract to a powder and subsequent re-hydration into an aqueous solution was evaluated. In an attempt to improve the shelf life of the lyophilized extract, dextran and sucrose were added during lyophilization. The stability of purified commercial urease following rehydration was also investigated. Results of the laboratory tests showed that the lyophilized crude extract maintained its activity during storage more effectively than either the crude extract solution or the rehydrated commercial urease. While incorporating 2% dextran (w/v) prior to lyophilization of the crude extract increased the overall enzymatic activity, it did not enhance the stability of the urease during storage.

scholarly journals Competing Conventions with Costly Information Acquisition

Games ◽  
2021 ◽  
Vol 12 (3) ◽  
pp. 53
Author(s):  
Roberto Rozzi
Keyword(s):  
Information Acquisition ◽  
Evolutionary Model ◽  
Equilibrium Selection ◽  
The Other ◽  
Group Interactions ◽  
Social Coordination ◽  
Long Run ◽  
Stochastic Stability Analysis ◽  
The Stability ◽  
The Cost

We consider an evolutionary model of social coordination in a 2 × 2 game where two groups of players prefer to coordinate on different actions. Players can pay a cost to learn their opponent’s group: if they pay it, they can condition their actions concerning the groups. We assess the stability of outcomes in the long run using stochastic stability analysis. We find that three elements matter for the equilibrium selection: the group size, the strength of preferences, and the information’s cost. If the cost is too high, players never learn the group of their opponents in the long run. If one group is stronger in preferences for its favorite action than the other, or its size is sufficiently large compared to the other group, every player plays that group’s favorite action. If both groups are strong enough in preferences, or if none of the groups’ sizes is large enough, players play their favorite actions and miscoordinate in inter-group interactions. Lower levels of the cost favor coordination. Indeed, when the cost is low, in inside-group interactions, players always coordinate on their favorite action, while in inter-group interactions, they coordinate on the favorite action of the group that is stronger in preferences or large enough.

scholarly journals Computing the Exact Number of Similarity Classes in the Longest Edge Bisection of Tetrahedra

Mathematics ◽  
2021 ◽  
Vol 9 (12) ◽  
pp. 1447
Author(s):  
Jose P. Suárez ◽  
Agustín Trujillo ◽  
Tania Moreno
Keyword(s):  
Data Structure ◽  
Stability Condition ◽  
Open Problem ◽  
Integer Arithmetic ◽  
Exact Number ◽  
Similarity Class ◽  
The Stability ◽  
High Level ◽  
The Cost

Showing whether the longest-edge (LE) bisection of tetrahedra meshes degenerates the stability condition or not is still an open problem. Some reasons, in part, are due to the cost for achieving the computation of similarity classes of millions of tetrahedra. We prove the existence of tetrahedra where the LE bisection introduces, at most, 37 similarity classes. This family of new tetrahedra was roughly pointed out by Adler in 1983. However, as far as we know, there has been no evidence confirming its existence. We also introduce a new data structure and algorithm for computing the number of similarity tetrahedral classes based on integer arithmetic, storing only the square of edges. The algorithm lets us perform compact and efficient high-level similarity class computations with a cost that is only dependent on the number of similarity classes.

Sign in / Sign up

Export Citation Format

Share Document