Comparison of the passive microwave spectral signature of the Antarctic ice sheet with ground traverse data

Surdyk, Sylviane; Fily, Michel

doi:10.1017/s0260305500012775

Cited by 21 publications

(20 citation statements)

References 5 publications

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“…Larger grain-sizes are found at M2 (itb4) and MDP (itb5) sites even at the surface. This is in agreement with older traverse data (Stuart and Heine, 1961) and could explain the peculiar microwave signature observed there (Surdyk and Fily, 1993). These sites are characterized by wind crust, consisting of a single snow-grain layer cemented by thin (0.1–2 mm) films of sublimated ice.…”

Section: Resultssupporting

confidence: 92%

“…Under strongly developed wind crust the depth-hoar layer clearly indicates prolonged sublimation due to a hiatus in accumulation and therefore a long, multi-annual, steep temperature-gradient metamorphism (Gow, 1965). Either the large grain or the wind crust (Wiesmann and others, 2000) could explain the peculiar microwave signature observed (Surdyk and Fily, 1993). Sites MDP (itb5) and MDPA (itb6) are only at a distance of 5 km, and show quite different grain-size profiles, both for mean values and for variability.…”

Section: Resultsmentioning

confidence: 99%

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Snow grain-size measurements in Antarctica

et al. 2002

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ABSTRACT. Grain-size is an important but not well-known characteristic of snow at the surface of Antarctica. In the past, grain-size has been reported using various methods, the reliability, reproducibility and intercomparability of which is not warranted. In this paper, we present and recommend, depending on available logistical support, three techniques of snow-grain sampling and/or imaging in the field as well as an original digital image-processing method, which we have proved provides reproducible and intercomparable measures of a snow grain-size parameter, the mean convex radius. Results from more than 500 samples and 3000 images of snow grains are presented, which yield a still spatially limited yet unprecedentedly wide picture of near-surface snow grain-size distribution from fieldwork in Antarctica. In particular, except at sites affected by a very particular meteorology, surface grains in the interior of the ice sheet are uniformly small (0.1^0.2 mm). The climate-related increase of grain-size with depth through metamorphism is, as expected, not spatially uniform. Our Antarctic snow grain-size database will continue to grow as field investigations bring new samples, images and measures of snow grain.

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Section: Resultssupporting

confidence: 92%

Section: Resultsmentioning

confidence: 99%

Snow grain-size measurements in Antarctica

et al. 2002

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“…Nevertheless, we provide here a broad comparison with in situ measurements acquired along traverses, as the same method was used over a wide distance and therefore presents consistency in space. Most of these data are summarized by Surdyk and Fily (1993).…”

Section: Validations and Discussionmentioning

confidence: 99%

“…In Wilkes Land, along the 69° S parallel, grain sizes were reported to be fairly constant between 112 and 131° E, and grain growth between the surface and 2 m depth was weak (Goodwin, 1988; Surdyk and Fily, 1993). The Wilkes Land profiles retrieved by satellite agree with these characteristics; the gradient is weak and the grain radius near the surface is moderate.…”

Section: Validations and Discussionmentioning

confidence: 99%

Snow grain-size profiles deduced from microwave snow emissivities in Antarctica

Brucker¹,

Picard²,

Fily³

2010

J. Glaciol.

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International audienceSpaceborne microwave radiometers are an attractive tool for observing Antarctic climate because their measurements are related to the snow temperature. However, the conversion from microwave emission to snow temperature is not simple and strongly depends on the emissivity through snow properties. This difficulty in predicting the snow property profile for Antarctic conditions is the main bottleneck in the retrieval of accurate climate information from microwave radiometers. We attempt to explain the vertically polarized emissivity at 19.3 and 37 GHz derived from brightness temperatures acquired by the Special Sensor Microwave/Imager (SSM/I) and physical temperature from the ERA-40 re-analysis. In Antarctica the snow emissivities at 19.3 and 37 GHz are nearly equal, although a decrease with frequency is expected. To explain this, we consider various profiles of snow grain size and density and predict their emissivity using a dense-medium radiative transfer (DMRT) model. The results show that the emissivities cannot be explained by constant profiles of grain size and density. Heterogeneous snowpacks need to be considered. We first test random variations of snow density and grain radius with depth and then monotonic and continuous variations in the snow grain radius. In both cases, we show that an overall increase of the snow grain radius with depth is required to match the observed emissivity in Antarctica. In addition, two parameters characterizing the snow grain profiles are retrieved and compared with (1) in situ measurements of grain size at various locations in East Antarctica, (2) grain size estimated using visible spaceborne radiometers and (3) a semi-empirical relationship for grain growth

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“…Surdyk and Fily [25] also show that stratification and subsurface layers lower brightness temperatures in horizontal polarization and thus enhance the temperature difference between both polarizations.…”

Section: Discussionmentioning

confidence: 91%

Dual-frequency Topex altimeter observations of Greenland

Rémy

Legrésy

Bleuzen

et al. 1996

Journal of Electromagnetic Waves and Applications

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Altimetric height can be underestimated on ice sheet surfaces, because of penetration of the radar wave inside the snowpack. Estimation of the induced bias is quite impossible, because of the large number of parameters involved both in surface and subsurface scattering. Indeed, altimetric echo of snow surface is controlled by antenna pattern, surface microroughness and kilometric roughness, internal stratification, scattering and extinction coefficient. Most of these parameters are radar frequency dependent, the dual-frequency Topex altimeter thus gives an opportunity to empirically detect this bias. Indeed, volume signal is clearly suggested by comparing the C-band and Ku-band altimeter heights and waveform parameters. Altimeter height difference are of a few decimeters only, and have kilometric scale variations: induced volume error seems to be more linked with the waveform deformation by the surface topography than with the intensity of the subsurface signal.

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Comparison of the passive microwave spectral signature of the Antarctic ice sheet with ground traverse data

Cited by 21 publications

References 5 publications

Snow grain-size measurements in Antarctica

Snow grain-size measurements in Antarctica

Snow grain-size profiles deduced from microwave snow emissivities in Antarctica

Dual-frequency Topex altimeter observations of Greenland

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