Dual-frequency altimeter signal from Envisat on the Amery ice-shelf
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...
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Online Access: | https://eprints.utas.edu.au/4499/ https://eprints.utas.edu.au/4499/1/4499.pdf https://doi.org/10.1016/j.rse.2007.01.007 |
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ftunivtasmania:oai:eprints.utas.edu.au:4499 2023-05-15T13:22:06+02:00 Dual-frequency altimeter signal from Envisat on the Amery ice-shelf Lacroix, P Legresy, B Coleman, R Dechambre, M Remy, F 2007-08 application/pdf https://eprints.utas.edu.au/4499/ https://eprints.utas.edu.au/4499/1/4499.pdf https://doi.org/10.1016/j.rse.2007.01.007 en eng United States https://eprints.utas.edu.au/4499/1/4499.pdf Lacroix, P, Legresy, B, Coleman, R, Dechambre, M and Remy, F 2007 , 'Dual-frequency altimeter signal from Envisat on the Amery ice-shelf' , Remote Sensing of Environment, vol. 109, no. 3 , pp. 285-294 , doi:10.1016/j.rse.2007.01.007 <http://dx.doi.org/10.1016/j.rse.2007.01.007>. 291001 Geodesy Radar altimetry Antartica Ice-shelf Snow properties Crevasses Radar waves penetration Article PeerReviewed 2007 ftunivtasmania https://doi.org/10.1016/j.rse.2007.01.007 2020-05-30T07:18:20Z 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. Article in Journal/Newspaper Amery Ice Shelf Antarc* Antarctica antartic* East Antarctica Ice Shelf University of Tasmania: UTas ePrints East Antarctica Amery ENVELOPE(-94.063,-94.063,56.565,56.565) Amery Ice Shelf ENVELOPE(71.000,71.000,-69.750,-69.750) Remote Sensing of Environment 109 3 285 294 |
institution |
Open Polar |
collection |
University of Tasmania: UTas ePrints |
op_collection_id |
ftunivtasmania |
language |
English |
topic |
291001 Geodesy Radar altimetry Antartica Ice-shelf Snow properties Crevasses Radar waves penetration |
spellingShingle |
291001 Geodesy Radar altimetry Antartica Ice-shelf Snow properties Crevasses Radar waves penetration Lacroix, P Legresy, B Coleman, R Dechambre, M Remy, F Dual-frequency altimeter signal from Envisat on the Amery ice-shelf |
topic_facet |
291001 Geodesy Radar altimetry Antartica Ice-shelf Snow properties Crevasses Radar waves penetration |
description |
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. |
format |
Article in Journal/Newspaper |
author |
Lacroix, P Legresy, B Coleman, R Dechambre, M Remy, F |
author_facet |
Lacroix, P Legresy, B Coleman, R Dechambre, M Remy, F |
author_sort |
Lacroix, P |
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 |
United States |
publishDate |
2007 |
url |
https://eprints.utas.edu.au/4499/ https://eprints.utas.edu.au/4499/1/4499.pdf https://doi.org/10.1016/j.rse.2007.01.007 |
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 antartic* East Antarctica Ice Shelf |
genre_facet |
Amery Ice Shelf Antarc* Antarctica antartic* East Antarctica Ice Shelf |
op_relation |
https://eprints.utas.edu.au/4499/1/4499.pdf Lacroix, P, Legresy, B, Coleman, R, Dechambre, M and Remy, F 2007 , 'Dual-frequency altimeter signal from Envisat on the Amery ice-shelf' , Remote Sensing of Environment, vol. 109, no. 3 , pp. 285-294 , doi:10.1016/j.rse.2007.01.007 <http://dx.doi.org/10.1016/j.rse.2007.01.007>. |
op_doi |
https://doi.org/10.1016/j.rse.2007.01.007 |
container_title |
Remote Sensing of Environment |
container_volume |
109 |
container_issue |
3 |
container_start_page |
285 |
op_container_end_page |
294 |
_version_ |
1766363276222922752 |