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Dual-frequency altimeter signal from Envisat on the Amery ice-shelf / Pascal Lacroix in Remote sensing of environment, vol 109 n° 3 (15 August 2007)  

Public [article]  inRemote sensing of environment > vol 109 n° 3 (15 August 2007) . - pp 285 - 294 Titre : Dual-frequency altimeter signal from Envisat on the Amery ice-shelf Type de document : Article/Communication Auteurs : Pascal Lacroix, Auteur ; Benoit Legrésy, Auteur ; et al., Auteur ; et al., Auteur Année de publication : 2007 Article en page(s) : pp 285 - 294 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Traitement du signal [Termes IGN] altimétrie par radar [Termes IGN] Antarctique [Termes IGN] bande S [Termes IGN] calotte glaciaire [Termes IGN] crevasse [Termes IGN] écho radar [Termes IGN] épaisseur de la glace [Termes IGN] image Envisat-AATSR [Termes IGN] réflectance de surface [Termes IGN] réflexion spéculaire [Termes IGN] traitement du signal [Termes IGN] variation saisonnière Résumé : (Auteur) In Antarctica, radar altimeter measurements are sensitive to dielectric and penetration properties of the sensed medium (snow) such that the spacecraft's altitude can be biased. Since 2002, relatively low frequency radar measurements over the Amery Ice Shelf, east Antarctica, have been acquired using the Envisat dual frequency altimeter at S (3.2 GHz) and Ku (13.6 GHz) bands, which penetrate a few meters into the firn. The altimeter signal is however modified in summer by the presence of snowfilled crevasses. Indeed, the specularity of the snow surfaces in summer makes the altimetric signal sensitive mostly to nadir echoes, that increases the ratio between the crevasse signal and the surrounding ice-shelf signal at nadir. Crevasses are distinguished by differences in backscattering behavior compared with the surrounding ice-shelf signal. Crevasses are characterized by a strong backscatter coefficient at Ku band and anomalies in the S band altitude estimation. These two characteristics make snowfilled crevasses detectable by the dual frequency altimeter of Envisat. We first retrieve the geometric properties of the crevasses using a hyperbolic shape function, created by strong crevasse backscatter in the Ku waveform measurements. From this retrieved crevasse signal and further waveform analysis, we assess the properties of the snow surface and its sub-surface. The crevasse, due to its small size compared to the altimeter footprint, is found to be an excellent target to study snow properties of the ice-shelf. The anomalies in the S band altitude measurements over crevasses can then be explained by the presence of a double echo in the S band waveforms. This echo is attributed to a reflection at the base of the snowbridge, where we see evidence of sub-surface echos in the individual altimeter waveforms. Based on this observation, a methodology is developed to estimate the thickness of the snowbridge. We calculate the penetration depths in the summer snow surface of the Amery at Ku band, that is found to be around 6 m. Copyright Elsevier Numéro de notice : A2007-312 Affiliation des auteurs : non IGN Thématique : IMAGERIE Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1016/j.rse.2007.01. En ligne : https://doi.org/10.1016/j.rse.2007.01.007 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=28675 [article]