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Radar altimeter waveform simulations in Antarctica with the Snow Microwave Radiative Transfer Model (SMRT) |
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Year |
2021 |
Publication |
Remote Sensing of Environment |
Abbreviated Journal |
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Volume |
263 |
Issue  |
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Pages |
112534 |
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Keywords |
Antarctic ice sheet Field measurements Modeling Radar altimetry Remote sensing SMRT Waveform |
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Abstract |
Radar altimeters are important tools to monitor the volume of the ice sheets. The penetration of radar waves in the snowpack is a major source of uncertainty to retrieve surface elevation. To correct this effect, a better understanding of the sensitivity of the radar waveforms to snow properties is needed. Here, we present an extension of the Snow Model Radiative Transfer (SMRT) to compute radar waveforms and conduct a series of simulations on the Antarctic ice sheet. SMRT is driven by snow and surface roughness properties measured over a large latitudinal range during two field campaigns on the Antarctic Plateau. These measurements show that the snowpack is rougher, denser, less stratified, warmer, and has smaller snow grains near the coast than on the central Plateau. These simulations are compared to satellite observations in the Ka, Ku, and S bands. SMRT reproduces the observed waveforms well. For all sites and all sensors, the main contribution comes from the surface echo. The echo from snow grains (volume scattering) represents up to 40% of the amplitude of the total waveform power in the Ka band, and less at the lower frequencies. The highest amplitude is observed on the central Plateau due to the combination of higher reflection from the surface, higher scattering by snow grains in the Ka and Ku bands, and higher inter-layer reflections in the S band. In the Ka band, the wave penetrates in the snowpack less deeply on the central Plateau than near the coast because of the strong scattering caused by the larger snow grains. The opposite is observed in the S band, the wave penetrates deeper on the central Plateau because of the lower absorption due to the lower snow temperatures. The elevation bias caused by wave penetration into the snowpack show a constant bias of 10 cm for all sites in the Ka band, and a bias of 11 cm, and 21 cm in the Ku band for sites close to the coast and the central Plateau, respectively. Now that SMRT is performing waveform simulations, further work will address how the snowpack properties affect the parameters retrieved by more advanced retracking algorithms such as ICE-2 for different snow cover surfaces. |
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1110 |
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0034-4257 |
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yes |
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7997 |
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Individual-based model of population dynamics in a sea urchin of the Kerguelen Plateau (Southern Ocean), Abatus cordatus, under changing environmental conditions |
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Year |
2021 |
Publication |
Ecological Modelling |
Abbreviated Journal |
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Volume |
440 |
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Pages |
109352 |
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Keywords |
Climate change Dynamic energy budget Ecological modelling Endemic echinoderm Individual-based model Kerguelen Model sensitivity |
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1044 |
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0304-3800 |
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yes |
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8002 |
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Title |
The high diversity of Southern Ocean sea stars (Asteroidea) reveals original evolutionary pathways |
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Year |
2021 |
Publication |
Progress in oceanography |
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Volume |
190 |
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Pages |
102472 |
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Keywords |
Antarctica Biodiversity COI mtDNA Echinodermata Evolution Phylogeography |
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Benthic life in the Southern Ocean (SO) features unique life history traits and species assemblages, but the origin and evolution of many of these taxonomic groups is still unclear. Sea stars (Asteroidea) are a diversified and abundant component of benthic ecosystems in the SO, in which they can play key ecological roles. Former studies suggest that the diversity of the entire class is still poorly known and underestimated, hampering the assessment of the origin and evolution of the class in the SO. In the present study, we analyse spatial patterns of SO sea star diversity using an occurrence database of ~14,000 entries. The biogeographic analysis is coupled with the exploration of an extensive molecular phylogeny based on over 4,400 specimen sequences to inform, support and/or question the observed diversity patterns. We show that the current taxonomy of SO asteroids needs revision and that their diversity has generally been overlooked and misinterpreted. Molecular results highlight the recent diversification of most studied taxa, at genus and species levels, which supports an evolutionary scenario referring to successive invasion and exchange events between the SO and adjacent regions, and clade diversification during periods of rapid environmental changes driven by the succession of glacial cycles. Our work advocates for employing, and endorsing the use of extensive genetic barcode libraries for biodiversity studies. |
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1044,1124 |
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Bachelor's thesis |
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0079-6611 |
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yes |
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8183 |
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2021 |
Publication |
Natural Hazards and Earth System Sciences Discussions |
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1-25 |
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133 |
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1561-8633 |
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yes |
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8019 |
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Echo occurrence in the southern polar ionosphere for the SuperDARN Dome C East and Dome C North radars |
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2021 |
Publication |
Polar Science |
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28 |
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100684 |
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Keywords |
Echo occurrence IRI model Polar cap radars Ray-tracing |
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In this paper, echo occurrence rates for the Dome C East (DCE) and the new Dome C North (DCN) radars are studied. We report the ionospheric and ground scatter echo occurrence rates for selected periods around equinoxes and solstices in the final part of the solar cycle XXIV. The occurrence maps built in Altitude Adjusted Corrected Geomagnetic latitude and Magnetic Local Time coordinates show peculiar patterns highly variable with season. The comparisons of the radar observations with the International Reference Ionosphere model electron density and with ray tracing simulations allow us to explain the major features of observed patterns in terms of electron density variations. The study shows the great potential of the DCE and DCN radar combination to the Super Dual Auroral Radar Network (SuperDARN) convection mapping in terms of monitoring key regions of the high-latitude ionosphere critical for understanding of the magnetospheric dynamics. |
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312 |
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1873-9652 |
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yes |
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8020 |
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Title |
Impact of socio-economic traditions on current tobacco and tea addictions (Siberia 17th to 20th century) |
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2021 |
Publication |
Medrxiv |
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Objective To investigate how tobacco and tea spread among virgin populations and how the first addictions have subsequently influenced the behavior of present-day populations. Design Retrospective observational study using data from frozen burials and levels of theobromine, theophylline, caffeine, nicotine, and cotinine measured in hair samples from frozen bodies of autochthonous people. Confrontation of the results with new ethnobotanical, historical and cultural data from the past and with present day epidemiological data from the same region. Setting Eastern Siberia (Yakutia) from the contact with Europeans (17th century) to the assimilation of people into Russian society (19th century). Participants 47 frozen bodies of autochthonous people from eastern Siberia and a review of present-day populations from Yakutia Intervention Levels of theobromine, theophylline, caffeine, nicotine, and cotinine were measured in hair samples. Along with the collection of cultural data associated with the bodies, potential comorbidities were investigated. Main outcome measure We combined LC-HRMS and LC-MS/MS tools for toxicological investigations in hair and we assessed the association between xenobiotic concentrations and geography using several permutation-based methods to infer the economic circuits of tobacco and tea. Comparison of the results obtained with ethno-botanical analyses allowed to identify the products from which the metabolites were derived. Results Hair levels of theobromine, theophylline and caffeine vary with the type of beverage consumed: green, black or local herbal teas. At the beginning of our study period, a few heavy consumers of tobacco were found among light or passive consumers. Tobacco-related co-morbidities began to be recorded one century after contact with Europeans. Heavy tea users were only found from the 19th century and the heaviest users of the two substances date from this century. After the first contact, teas were widely consumed as beverages and medicines but also for shamanic reasons. Economic factors, fashion and social and family contacts seem to have played a decisive role in tobacco consumption very early on. Conclusion Epidemiological characteristics of present-day Yakutia suggest that the high prevalence of smokers and tea consumers, the prevalence of female smokers and tobacco use in the north, find their origins in the diffusion phenomena of the 18th and 19th century. Behavioral evolution governed the process of substance integration and was determinant for the continuity of use of these substances over a long period of time. |
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1038 |
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7952 |
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Title |
Seasonal variation of mercury contamination in Arctic seabirds: A pan-Arctic assessment |
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2021 |
Publication |
Science of The Total Environment |
Abbreviated Journal |
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750 |
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Pages |
142201 |
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Keywords |
Feathers Metal Polar Seasonal variation Top predators |
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Abstract |
Mercury (Hg) is a natural trace element found in high concentrations in top predators, including Arctic seabirds. Most current knowledge about Hg concentrations in Arctic seabirds relates to exposure during the summer breeding period when researchers can easily access seabirds at colonies. However, the few studies focused on winter have shown higher Hg concentrations during the non-breeding period than breeding period in several tissues. Hence, improving knowledge about Hg exposure during the non-breeding period is crucial to understanding the threats and risks encountered by these species year-round. We used feathers of nine migratory alcid species occurring at high latitudes to study bird Hg exposure during both the breeding and non-breeding periods. Overall, Hg concentrations during the non-breeding period were ~3 times higher than during the breeding period. In addition, spatial differences were apparent within and between the Atlantic and Pacific regions. While Hg concentrations during the non-breeding period were ~9 times and ~3 times higher than during the breeding period for the West and East Atlantic respectively, Hg concentrations in the Pacific during the non-breeding period were only ~1.7 times higher than during the breeding period. In addition, individual Hg concentrations during the non-breeding period for most of the seabird colonies were above 5 ?g g?1 dry weight (dw), which is considered to be the threshold at which deleterious effects are observed, suggesting that some breeding populations might be vulnerable to non-breeding Hg exposure. Since wintering area locations, and migration routes may influence seasonal Hg concentrations, it is crucial to improve our knowledge about spatial ecotoxicology to fully understand the risks associated with Hg contamination in Arctic seabirds. |
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0048-9697 |
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yes |
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8026 |
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Strong migratory connectivity across meta-populations of sympatric North Atlantic seabirds |
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2021 |
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Marine Ecology Progress Series |
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SEA |
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Environmental niche Inter-population mixing Large-scale spatiotemporal dynamics Light-level geolocation Murres Population spread Seasonality |
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388 |
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0171-8630, 1616-1599 |
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yes |
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8027 |
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Author |
Andreas Richter, Alexey A. Ekaykin, Matthias O. Willen, Vladimir Ya. Lipenkov, Andreas Groh, Sergey V. Popov, Mirko Scheinert, Martin Horwath, Reinhard Dietrich |
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Title |
Surface Mass Balance Models Vs. Stake Observations: A Comparison in the Lake Vostok Region, Central East Antarctica |
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2021 |
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Frontiers in Earth Science |
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9 |
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388 |
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411 |
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2296-6463 |
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8030 |
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Anzhou Cao, Zheng Guo, Xiaoyu Qi, Peiliang Li, Hailun He |
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Title |
Seasonal and nodal variations of predominant tidal constituents in the global ocean |
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2021 |
Publication |
Continental Shelf Research |
Abbreviated Journal |
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217 |
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104372 |
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Fitting Modified two-step harmonic analysis Nodal modulation Seasonal variation Tide gauge Tides |
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Tides are one of the basic types of ocean water motions. Previous studies have reported that the M2 constituent exhibits seasonal variations (annual cycles) in some regions. However, based on the newly proposed method of modified two-step harmonic analysis (HA) and its application at 240 global tide gauges, we find that the M2 constituent as well as the S2 and K1 do not have significant seasonal variations at these tide gauges. The seasonal variations of the M2 constituent reported in previous studies are caused by its satellites, the H1 and H2 constituents, which are not resolved in these studies due to the short time window (one month or three months) used in HA. Because the frequency of the H1 (H2) constituent is equal to that of the M2 minus (plus) the frequency of annual cycles, the superposition of the M2, H1 and H2 constituents with constant amplitudes is equivalent to the M2 constituent with seasonally varying amplitudes. Compared with the new method, some adaptations to traditional HA aiming to capture variations in amplitudes and phase lags of constituents have some limitations, because they either neglect some satellites of the major constitutes or introduce spurious fluctuations resulting from an unreasonably large number of independent points. The nodal modulations of predominant constituents are also explored in this study. On the global scale, the nodal modulations of the M2, K1 and O1 constituents agree with the theoretical predictions, except a cold spot region with reduced nodal modulation in the Gulf of Maine and a hot spot region with enhanced nodal modulation in the South China Sea for the M2. Nodal modulation is also found for the S2 constituent (in theory, the S2 has no nodal modulation), which is 0.8% averaged at 164 tide gauges where the S2 is not too weak. |
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688 |
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0278-4343 |
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8032 |
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