Dual-frequency altimeter signal from Envisat on the Amery ice-shelf
0034-4257 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 bee...
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ftmeteofrance:oai:HAL:hal-00402155v1 2024-04-07T07:46:07+00:00 Dual-frequency altimeter signal from Envisat on the Amery ice-shelf Lacroix, Pierre Legresy, B. Coleman, R. Dechambre, Monique Remy, F. Laboratoire d'études en Géophysique et océanographie spatiales (LEGOS) Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3) Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire Midi-Pyrénées (OMP) Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales Toulouse (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France-Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales Toulouse (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France-Centre National de la Recherche Scientifique (CNRS) 2007 https://hal.science/hal-00402155 en eng HAL CCSD Elsevier hal-00402155 https://hal.science/hal-00402155 ISSN: 0034-4257 EISSN: 1879-0704 Remote Sensing of Environment https://hal.science/hal-00402155 Remote Sensing of Environment, 2007, 109 (3), pp.285-294 info:eu-repo/semantics/article Journal articles 2007 ftmeteofrance 2024-03-14T18:10:54Z 0034-4257 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 fim. 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 ... Article in Journal/Newspaper Amery Ice Shelf Antarc* Antarctica East Antarctica Ice Shelf Météo-France: HAL East Antarctica Amery ENVELOPE(-94.063,-94.063,56.565,56.565) Amery Ice Shelf ENVELOPE(71.000,71.000,-69.750,-69.750) |
institution |
Open Polar |
collection |
Météo-France: HAL |
op_collection_id |
ftmeteofrance |
language |
English |
description |
0034-4257 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 fim. 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 ... |
author2 |
Laboratoire d'études en Géophysique et océanographie spatiales (LEGOS) Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3) Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire Midi-Pyrénées (OMP) Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales Toulouse (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France-Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales Toulouse (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France-Centre National de la Recherche Scientifique (CNRS) |
format |
Article in Journal/Newspaper |
author |
Lacroix, Pierre Legresy, B. Coleman, R. Dechambre, Monique Remy, F. |
spellingShingle |
Lacroix, Pierre Legresy, B. Coleman, R. Dechambre, Monique Remy, F. Dual-frequency altimeter signal from Envisat on the Amery ice-shelf |
author_facet |
Lacroix, Pierre Legresy, B. Coleman, R. Dechambre, Monique Remy, F. |
author_sort |
Lacroix, Pierre |
title |
Dual-frequency altimeter signal from Envisat on the Amery ice-shelf |
title_short |
Dual-frequency altimeter signal from Envisat on the Amery ice-shelf |
title_full |
Dual-frequency altimeter signal from Envisat on the Amery ice-shelf |
title_fullStr |
Dual-frequency altimeter signal from Envisat on the Amery ice-shelf |
title_full_unstemmed |
Dual-frequency altimeter signal from Envisat on the Amery ice-shelf |
title_sort |
dual-frequency altimeter signal from envisat on the amery ice-shelf |
publisher |
HAL CCSD |
publishDate |
2007 |
url |
https://hal.science/hal-00402155 |
long_lat |
ENVELOPE(-94.063,-94.063,56.565,56.565) ENVELOPE(71.000,71.000,-69.750,-69.750) |
geographic |
East Antarctica Amery Amery Ice Shelf |
geographic_facet |
East Antarctica Amery Amery Ice Shelf |
genre |
Amery Ice Shelf Antarc* Antarctica East Antarctica Ice Shelf |
genre_facet |
Amery Ice Shelf Antarc* Antarctica East Antarctica Ice Shelf |
op_source |
ISSN: 0034-4257 EISSN: 1879-0704 Remote Sensing of Environment https://hal.science/hal-00402155 Remote Sensing of Environment, 2007, 109 (3), pp.285-294 |
op_relation |
hal-00402155 https://hal.science/hal-00402155 |
_version_ |
1795662694492143616 |