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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]

Aerosol optical depth and land surface reflectance from multiangle AATSR measurements: global validation and intersensor comparisons / W.M.F. Grey in IEEE Transactions on geoscience and remote sensing, vol 44 n° 8 (August 2006)  

Public [article]  inIEEE Transactions on geoscience and remote sensing > vol 44 n° 8 (August 2006) . - pp 2184 - 2197 Titre : Aerosol optical depth and land surface reflectance from multiangle AATSR measurements: global validation and intersensor comparisons Type de document : Article/Communication Auteurs : W.M.F. Grey, Auteur ; P.R.J. North, Auteur ; S.O. Los, Auteur ; R.M. Mitchell, Auteur Année de publication : 2006 Article en page(s) : pp 2184 - 2197 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Traitement d'image [Termes IGN] aérosol [Termes IGN] analyse comparative [Termes IGN] diffusion du rayonnement [Termes IGN] épaisseur optique [Termes IGN] image Envisat-AATSR [Termes IGN] image Terra-MISR [Termes IGN] image Terra-MODIS [Termes IGN] Total ozone mapping spectrometer Résumé : (Auteur) This paper presents the results and satellite intercomparisons for the retrieval of aerosol optical depth (AOD) and land surface bidirectional reflectance using the Multiangle Advanced Along-Track Scanning Radiometer (AATSR). The algorithm developed is based on inversion of a physical model of light scattering that requires no a priori knowledge of the land surface. The model is evaluated for a number of sites around the world to test its operation over a range of aerosol types and land covers including dark and bright surfaces. Validation is performed using Aerosol Robotic Network ground-based sun-photometer measurements and by intercomparison with independent estimates of AOD derived from spaceborne instruments including Multiangle Imaging Spectroradiometer (MISR), Moderate Resolution Imaging Spectroradiometer (MODIS), and Total Ozone Mapping Spectrometer (TOMS) aerosol products. Results show good agreement (Pearson's correlation coefficient r2=0.70 for all sites combined) between the AATSR-derived estimates of AOD and the sun-photometer measurements. There is also a high correlation (r2=0.84) between the AATSR- and MISR-derived AOD estimates, but the correlations of the AATSR-derived AOD with MODIS-derived AOD and TOMS aerosol index are lower. In addition, the ability of the sensor to discriminate between different aerosol types is evaluated. Moreover, the estimates of the aerosol properties are used for atmospheric correction of the top-of-atmosphere reflectance. The AATSR surface reflectances are compared with the MODIS bidirectional reflectance distribution function/Albedo and MISR surface products and are shown to correspond with root-mean-square errors of 0.03 and 0.06 or better, respectively. The retrieval method is applied on an image basis resulting in an image of surface reflectance and a separate map of AOD. A map of AOD at 550 nm covering the Sahel and southern Sahara region is presented to demonstrate operation at regional and potentially global scales. Copyright IEEE Numéro de notice : A2006-394 Affiliation des auteurs : non IGN Thématique : IMAGERIE Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1109/TGRS.2006.872079 En ligne : https://ieeexplore.ieee.org/document/1661807 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=28118 [article]

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065-06081	RAB	Revue	Centre de documentation	En réserve L003	Disponible

Snow cover monitoring in Alpine regions using ENVISAT optical data / M. Pepe in International Journal of Remote Sensing IJRS, vol 26 n° 21 (November 2005)  

Public [article]  inInternational Journal of Remote Sensing IJRS > vol 26 n° 21 (November 2005) . - pp 4661 - 4667 Titre : Snow cover monitoring in Alpine regions using ENVISAT optical data Type de document : Article/Communication Auteurs : M. Pepe, Auteur ; P.A. Brivio, Auteur ; A. Rampini, Auteur ; et al., Auteur Année de publication : 2005 Article en page(s) : pp 4661 - 4667 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Applications de télédétection [Termes IGN] Alpes [Termes IGN] Aoste (val d') [Termes IGN] carte thématique [Termes IGN] classification floue [Termes IGN] détection des nuages [Termes IGN] image Envisat-AATSR [Termes IGN] image Envisat-MERIS [Termes IGN] image optique [Termes IGN] Lombardie [Termes IGN] manteau neigeux [Termes IGN] nébulosité [Termes IGN] Piémont (Italie) [Termes IGN] surveillance météorologique Résumé : (Auteur) The ENVISAT mission with a suite of high performance sensors offers some opportunities for mapping snow cover at regional and catchment scales. The spatial resolution of the Medium Resolution Imaging Spectrometer Instrument (MERIS) data and the spectral characteristics of the Advanced Along Track Scanning Radiometer (AATSR) data are suitable for these purposes. A new approach has been developed for the generation of snow cover products in Alpine regions, based on the combined use of ENVISAT optical data and topographic information. The Alpine region is selected as a test area to demonstrate the potential and the limitations of the novel approach. In particular, attention is focused on three regions of northern Italy (Valle d'Aosta, Piemonte, Lombardia). The first results obtained by the application of this new method to Earth Observation data will be presented and analysed. Numéro de notice : A2005-467 Affiliation des auteurs : non IGN Thématique : IMAGERIE Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1080/01431160500206635 En ligne : https://doi.org/10.1080/01431160500206635 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=27603 [article]

Exemplaires(1)

Code-barres	Cote	Support	Localisation	Section	Disponibilité
080-05211	RAB	Revue	Centre de documentation	En réserve L003	Disponible