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Polarization dependence of azimuth cutoff from quad-pol SAR images / Huimin Li in IEEE Transactions on geoscience and remote sensing, vol 57 n° 12 (December 2019)  

Public [article]  inIEEE Transactions on geoscience and remote sensing > vol 57 n° 12 (December 2019) . - pp 9878 - 9887 Titre : Polarization dependence of azimuth cutoff from quad-pol SAR images Type de document : Article/Communication Auteurs : Huimin Li, Auteur ; Alexis Mouche, Auteur ; He Wang, Auteur ; Justin E. Stopa, Auteur ; Bertrand Chapron, Auteur Année de publication : 2019 Article en page(s) : pp 9878 - 9887 Note générale : bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Traitement d'image radar et applications [Termes IGN] angle d'incidence [Termes IGN] azimut [Termes IGN] données polarimétriques [Termes IGN] image Gaofen [Termes IGN] image radar moirée [Termes IGN] image Radarsat [Termes IGN] polarisation [Termes IGN] polarisation croisée [Termes IGN] surface de la mer [Termes IGN] transformation non linéaire [Termes IGN] vague Résumé : (auteur) Although basic understanding of the synthetic aperture radar (SAR) imaging mechanism of ocean waves has been achieved, challenges still remain. In this paper, a large number of quad-polarized SAR images are analyzed to help assess how the standard SAR imaging transformation applies to all polarization channels. Foremost, the azimuth cutoff, a parameter essentially governed by the detected wave motions, is today solely related to radar configuration and the ocean wave spectrum but not to the polarization configuration. As obtained, the analyses based on quad-polarized Radarsat-2 and Gaofen-3 products document the distinct dependence of azimuth cutoff on polarization and incidence angle. Especially for cross-polarized VH measurements, azimuth cutoff estimates are generally larger than copolarized HH ones, the latter already being larger than values estimated under VV configuration. This trend increases with the incidence angle. The systematic comparisons between SAR measurements and simulations further demonstrate that the present SAR nonlinear transformation may not properly take into account the differing coherence time associated with the multi-polarized observation of ocean scenes. In particular, to reproduce the large azimuth cutoff parameters of cross-polarized images, a reduced coherence time shall be expected. This measurable sensitivity shall enhance the capabilities of polarized SAR systems to precisely derive more ocean surface properties, especially the influence of wave breakers, by combining both the copolarization and cross-polarization measurements. Numéro de notice : A2019-601 Affiliation des auteurs : non IGN Thématique : IMAGERIE Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1109/TGRS.2019.2929835 Date de publication en ligne : 14/08/2019 En ligne : http://doi.org/10.1109/TGRS.2019.2929835 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=94602 [article]

Calibration of the normalized radar cross section for sentinel-1 wave mode / Huimin Li in IEEE Transactions on geoscience and remote sensing, vol 57 n° 3 (March 2019)  

Public [article]  inIEEE Transactions on geoscience and remote sensing > vol 57 n° 3 (March 2019) . - pp 1514 - 1522 Titre : Calibration of the normalized radar cross section for sentinel-1 wave mode Type de document : Article/Communication Auteurs : Huimin Li, Auteur ; Alexis Mouche, Auteur ; Justin E. Stopa, Auteur ; Bertrand Chapron, Auteur Année de publication : 2019 Article en page(s) : pp 1514 - 1522 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Traitement d'image radar et applications [Termes IGN] Amazonie [Termes IGN] étalonnage radiométrique [Termes IGN] forêt équatoriale [Termes IGN] image Sentinel-SAR [Termes IGN] résidu Résumé : (Auteur) Sentinel-1 (S-1) is a two-satellite constellation for continuity of operational synthetic aperture radar (SAR) observations. Wave mode (WV) is the default mode over open ocean for S-1 to monitor global ocean waves and wind field. Therefore, proper radiometric calibration is essential to accurately infer these geophysical quantities. Based on the global data set acquired by S-1A WV, assessment of normalized radar cross section (NRCS) is carried out through comparison with CMOD5.N predictions over open ocean. The calibration accuracy quantified by NRCS residuals between SAR measurements and CMOD5.N demonstrates distinct features for two incidence angles (23.8° and 36.8°). Particularly, NRCS at 23.8° is overall consistent with CMOD5.N, while NRCS at 36.8° displays great deviation. Two recalibration methods are then implemented by examining the backscattering profile over Amazon rain forest and ocean calibration. Both methods show the necessity for recalibration and obtain comparable correction factors for WV1 and WV2, respectively. The NRCS residuals by applying both methods are significantly reduced toward zero. By comparison, ocean calibration is more efficient and practical to implement. Numéro de notice : A2019-128 Affiliation des auteurs : non IGN Thématique : FORET/IMAGERIE Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1109/TGRS.2018.2867035 Date de publication en ligne : 14/09/2018 En ligne : https://doi.org/10.1109/TGRS.2018.2867035 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=92457 [article]

Global observations of ocean surface winds and waves using spaceborne synthetic aperture radar measurements / Huimin Li (2019)  

Public Titre : Global observations of ocean surface winds and waves using spaceborne synthetic aperture radar measurements Type de document : Thèse/HDR Auteurs : Huimin Li, Auteur Editeur : Institut Mines-Télécom Atlantique IMT Atlantique Année de publication : 2019 Importance : 163 p. Format : 21 x 30 cm Note générale : Bibliographie Thèse de Doctorat de l'Ecole Nationale Supérieure des Mines-Telecom Atlantique Bretagne Pays de la Loire-IMT Atlantique, en Sciences de la Mer et du littoral : Spécialité : Océanographie, Physique et Environnement Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Traitement d'image radar et applications [Termes IGN] angle d'incidence [Termes IGN] étalonnage des données [Termes IGN] fonction de transfert de modulation [Termes IGN] houle [Termes IGN] image Envisat-ASAR [Termes IGN] image Gaofen [Termes IGN] image radar moirée [Termes IGN] image Radarsat [Termes IGN] image Sentinel-SAR [Termes IGN] océan [Termes IGN] phénomène météorologique [Termes IGN] polarisation croisée [Termes IGN] radar à antenne synthétique [Termes IGN] rapport signal sur bruit [Termes IGN] tempête [Termes IGN] vague [Termes IGN] vent Index. décimale : THESE Thèses et HDR Résumé : (auteur) Spaceborne synthetic aperture radar (SAR) has been demonstrated invaluable in observing the global ocean winds and waves. SAR images acquired by multiple sensors are employed, including Sentinel-1(S-1), Envisat/ASAR, Gaofen-3 and Radarsat-2. This thesis reviews the commonly used SAR parameters (NRCS and azimuth cutoff) in the first part. A series of calibration steps are required to obtain a proper NRCS and assessment of NRCS is carried out for S-1wave mode (WV). It turns out that WV is poorly calibrated and is thus re-calibrated to obtain accurate NRCS. Azimuth cut off is demonstrated to be complementary to NRCS and can account for the sea state impact on the wind retrieval. Based on the available fully polarimetric SAR products, azimuth cut off is found to vary greatly with polarizations. The present SAR mapping transformation is sufficient to interpret the co-polarized azimuth cut off, while not for the cross-polarization. With the limitations of SAR imaging in mind, a new parameter is proposed and defined based on the SAR image cross-spectra, termed as MACS. The imaginary part of MACS is found to be a signed quantity relative to the wind direction. Given this dependence, an independent wind retrieval algorithm is expected to benefit. The magnitude of MACS is able to aid for estimate of modulation function of SAR mapping. In addition, MACS also gives promising results regarding the global wave studies. The global signatures of MACS at various wave lengths are well representative of the winds distributions, spatially and seasonally. MACS of long waves shows greater values over the storm tracks while the shorter waves are mostly within the trader winds. These results are expected to help evaluate the model outputs and complement further studies of the global wave spectral climate. Data continuity in the coming 10 years shall extend the study towards longer duration. Note de contenu : I- Background and study of the existing SAR parameters Chap. 1 - Background Chap. 2 - SAR imaging of the ocean surface Chap. 3 - Status and challenges in SAR winds Chap. 4 - Azimuth cutoff of polarimetric SAR images II- A new SAR parameter and its applications in wind/wave study Chap. 5 - A new SAR parameter: MACS and its directionality Chap. 6 - Statistics of MACS magnitude and derived RAR MTF Chap. 7 - Investigation of global ocean waves using SAR MACS Chap. 8 - Conclusion and perspectives Numéro de notice : 25729 Affiliation des auteurs : non IGN Thématique : IMAGERIE Nature : Thèse française Note de thèse : Thèse de Doctorat : Océanographie, Physique et Environnement : Ecole nationale supérieure Mines-Télécom Atlantique : 2019 Organisme de stage : Ifremer nature-HAL : Thèse DOI : sans En ligne : https://tel.archives-ouvertes.fr/tel-02164506/document Format de la ressource électronique : URL Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=94895

Relating statistical characteristics of cross-polarized phase difference to speckle noise / Huimin Li in Journal of applied remote sensing, vol 9 (2015)  

Public [article]  inJournal of applied remote sensing > vol 9 (2015) . - 8 p. Titre : Relating statistical characteristics of cross-polarized phase difference to speckle noise Type de document : Article/Communication Auteurs : Huimin Li, Auteur ; Yunhua Wang, Auteur Année de publication : 2015 Article en page(s) : 8 p. Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Traitement d'image radar et applications [Termes IGN] données polarimétriques [Termes IGN] filtrage du bruit [Termes IGN] image radar moirée [Termes IGN] matrice de covariance [Termes IGN] phase [Termes IGN] polarimétrie radar [Termes IGN] polarisation croisée Résumé : (auteur) A qualitative relationship between the statistical behavior of cross-polarized phase difference ϕhvvh and dominant noise type is examined based on the polarimetric noise model proposed. The noise model focusing on the covariance matrix is able to separate the multiplicative noise which only affects the amplitude from the additive noise that alters both the amplitude and phase. In the case of low noise, the phase is not affected by the noise and ϕhvvh distribution is predicted to be centered at 0 deg in terms of reciprocity theorem. The case of strong noise is much more complicated as the dominant noise type plays an important role in the statistics of ϕhvvh. The phase over the area where multiplicative noise dominates is not altered, thus the ϕhvvh distribution is expected to have similar behaviors to the case of low noise. However, the dominant additive noise would significantly affect the phase so that an obvious deviation from 0 deg for ϕhvvh distribution is expected. Experiments with Radarsat-2 full polarimetric imageries further validate this qualitative relationship. Numéro de notice : A2015-101 Affiliation des auteurs : non IGN Thématique : IMAGERIE Nature : Article DOI : 10.1117/1.JRS.9.090599 En ligne : http://remotesensing.spiedigitallibrary.org/article.aspx?articleid=2091528 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=75392 [article]