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Open AccessArticle

Retrieval of the Absorption Coefficient of L-Band Radiation in Antarctica From SMOS Observations

1
University Grenoble Alpes, CNRS, IRD, Grenoble-INP, IGE, 38000 Grenoble, France
2
Institute of Applied Physics “Nello Carrara”—National Research Council—IFAC—CNR, 50019 Sesto Fiorentino, Italy
3
Laboratoire des Sciences du Climat et de l’Environnement (LSCE), Vallée Bât. 12, avenue de la Terrasse, 91198 Gif-sur-Yvette, France
*
Author to whom correspondence should be addressed.
Remote Sens. 2018, 10(12), 1954; https://doi.org/10.3390/rs10121954
Received: 31 October 2018 / Revised: 27 November 2018 / Accepted: 30 November 2018 / Published: 5 December 2018
(This article belongs to the Section Remote Sensing in Geology, Geomorphology and Hydrology)
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Abstract

Microwave emissions at the L-band (1–2 GHz) in Antarctica are characterized by a significant contribution of ice layers at great depth, from hundreds to a thousand meters. Brightness temperatures, thus, could provide the internal temperature of the ice sheet. However, there are two difficulties to overcome in developing an accurate retrieval algorithm. First, it is difficult to know precisely from which depths waves are emanating because the ice-absorption coefficient is uncertain at the L-band, despite several formulations proposed in the literature over the past few decades. Second, emissivity potentially varies in Antarctica due to remnant scattering in firn (or ice), even at the Brewster angle, and despite the low frequency, limiting the accuracy of the estimate of the physical temperature. Here, we present a retrieval method able to disentangle the absorption and emissivity effects from brightness temperature over the whole continent. We exploit the fact that scattering and absorption are controlled by different physical parameters and phenomena that can be considered as statistically independent. This independence provides a constraint to the retrieval method, that is then well-conditioned and solvable. Our results show that (1) the retrieved absorption agrees with the permittivity model proposed by Mätzler et al. (2006), and (2) emissivity shows significant variations, up to 6% over the continent, which are correlated with wind speed and accumulation patterns. A possible cause of this latter point is density heterogeneity and sastrugi buried in the firn. These two results are an important step forward for the accurate retrieval of internal temperature using low-frequency microwave radiometers. View Full-Text
Keywords: passive microwave; Band L; SMOS; Antarctica; brightness temperature; emissivity; permittivity; absorption coefficient passive microwave; Band L; SMOS; Antarctica; brightness temperature; emissivity; permittivity; absorption coefficient
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).
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MDPI and ACS Style

Passalacqua, O.; Picard, G.; Ritz, C.; Leduc-Leballeur, M.; Quiquet, A.; Larue, F.; Macelloni, G. Retrieval of the Absorption Coefficient of L-Band Radiation in Antarctica From SMOS Observations. Remote Sens. 2018, 10, 1954.

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