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R. Olmi, M. Bittelli, G. Picard, L. Arnaud, A. Mialon, S. Priori. (2021). Investigating the influence of the grain size and distribution on the macroscopic dielectric properties of Antarctic firn (Vol. 185).
Keywords: Antarctica Close?off Dielectric measurements Dielectric model Firn Full wave EM simulations Ice cores
Programme: 1110
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. (2021). Radar altimeter waveform simulations in Antarctica with the Snow Microwave Radiative Transfer Model (SMRT) (Vol. 263).
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.
Keywords: Antarctic ice sheet Field measurements Modeling Radar altimetry Remote sensing SMRT Waveform
Programme: 1110
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Alexander Kokhanovsky, Simon Gascoin, Laurent Arnaud, Ghislain Picard. (2021). Retrieval of Snow Albedo and Total Ozone Column from Single-View MSI/S-2 Spectral Reflectance Measurements over Antarctica (Vol. 13).
Keywords: albedo inverse problems light scattering radiative transfer snow snow grain size
Programme: 1110
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. (2021). Water Isotopic Signature of Surface Snow Metamorphism in Antarctica (Vol. 48).
Abstract: Water isotope ratios of ice cores are a key source of information on past temperatures. Through fractionation within the hydrological cycle, temperature is imprinted in the water isotopic composition of snowfalls. However, this signal of climatic interest is modified after deposition when snow remains at the surface exposed to the atmosphere. Comparing time series of surface snow isotopic composition at Dome C with satellite observations of surface snow metamorphism, we found that long summer periods without precipitation favor surface snow metamorphism altering the surface snow isotopic composition. Using excess parameters (combining D,17O, and 18O fractions) allow the identification of this alteration caused by sublimation and condensation of surface hoar. The combined measurement of all three isotopic compositions could help identifying ice core sections influenced by snow metamorphism in sites with very low snow accumulation.
Keywords: excess Ice cores metamorhism Paleoclimate water isotopes
Programme: 1110
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. (2021). (Vol. 13).
Abstract: The global climate shift currently underway has significant impacts on both the quality and quantity of snow precipitation. This directly influences the spatial variability of the snowpack as well as cumulative snow height. Contemporary glacier retreat reorganizes periglacial morphology: while the glacier area decreases, the moraine area increases. The latter is becoming a new water storage potential that is almost as important as the glacier itself, but with considerably more complex topography. Hence, this work fills one of the missing variables of the hydrological budget equation of an arctic glacier basin by providing an estimate of the snow water equivalent (SWE) of the moraine contribution. Such a result is achieved by investigating Structure from Motion (SfM) image processing that is applied to pictures collected from an Unmanned Aerial Vehicle (UAV) as a method for producing snow depth maps over the proglacial moraine area. Several UAV campaigns were carried out on a small glacial basin in Spitsbergen (Arctic): the measurements were made at the maximum snow accumulation season (late April), while the reference topography maps were acquired at the end of the hydrological year (late September) when the moraine is mostly free of snow. The snow depth is determined from Digital Surface Model (DSM) subtraction. Utilizing dedicated and natural ground control points for relative positioning of the DSMs, the relative DSM georeferencing with sub-meter accuracy removes the main source of uncertainty when assessing snow depth. For areas where snow is deposited on bare rock surfaces, the correlation between avalanche probe in-situ snow depth measurements and DSM differences is excellent. Differences in ice covered areas between the two measurement techniques are attributed to the different quantities measured: while the former only measures snow accumulation, the latter includes all of the ice accumulation during winter through which the probe cannot penetrate, in addition to the snow cover. When such inconsistencies are observed, icing thicknesses are the source of the discrepancy that is observed between avalanche probe snow cover depth measurements and differences of DSMs.
Keywords: arctic cryosphere moraine photogrammetry snow water equivalent snowcover spatial dynamics UAV-SfM
Programme: 1108
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. (2021). (Vol. 44).
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Candice Michelot, Akiko Kato, Thierry Raclot, Yan Ropert-Coudert. (2021). (Vol. 16).
Keywords: Animal behavior Animal sexual behavior Animal sociality Birds Foraging Nesting habits Penguins Reproductive success
Programme: 1091
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. (2021). Exploring the interplay between nest vocalizations and foraging behaviour in breeding birds (Vol. 180).
Keywords: bird communication foraging behaviour reproductive partner vocalization
Programme: 1091
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Noor Johnson, Matthew L Druckenmiller, Finn Danielsen, Peter L Pulsifer. (2021). The Use of Digital Platforms for Community-Based Monitoring (Vol. 71). Bachelor's thesis, , .
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Hajo Eicken, Finn Danielsen, Josephine-Mary Sam, Maryann Fidel, Noor Johnson, Michael K Poulsen, Olivia A Lee, Katie V Spellman, Lisbeth Iversen, Peter Pulsifer, Martin Enghoff. (2021). Connecting Top-Down and Bottom-Up Approaches in Environmental Observing (Vol. 71). Bachelor's thesis, , .
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