Automatic cloud screening in NOAA-AVHRR day-time imagery

• Main Authors: Wald, Lucien, Sèze, Geneviève, Desbois, Michel
• Other Authors: CEP/Sophia, Centre Énergétique et Procédés (CEP), Mines Paris - PSL (École nationale supérieure des mines de Paris), Université Paris Sciences et Lettres (PSL)-Université Paris Sciences et Lettres (PSL)-Mines Paris - PSL (École nationale supérieure des mines de Paris), Université Paris Sciences et Lettres (PSL)-Université Paris Sciences et Lettres (PSL), Laboratoire de Météorologie Dynamique (UMR 8539) (LMD), Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut national des sciences de l'Univers (INSU - CNRS)-École polytechnique (X), Institut Polytechnique de Paris (IP Paris)-Institut Polytechnique de Paris (IP Paris)-École des Ponts ParisTech (ENPC)-Centre National de la Recherche Scientifique (CNRS)-Département des Géosciences - ENS Paris, École normale supérieure - Paris (ENS-PSL), Université Paris Sciences et Lettres (PSL)-Université Paris Sciences et Lettres (PSL)-École normale supérieure - Paris (ENS-PSL)
• Format: Conference Object
• Language: English
• Published: HAL CCSD 1991
• Subjects: [SDU.OCEAN]Sciences of the Universe [physics]/Ocean; Atmosphere; [SPI.SIGNAL]Engineering Sciences [physics]/Signal and Image processing; [INFO.INFO-TS]Computer Science [cs]/Signal and Image Processing; Tromsoe
• Online Access: https://minesparis-psl.hal.science/hal-00464349; https://minesparis-psl.hal.science/hal-00464349/document; https://minesparis-psl.hal.science/hal-00464349/file/hal-00464349_auteur.pdf

International audience We evaluate how much of the cloud cover can be retrieved using only visible and near infrared informations from a wide-field sensor without thermal infrared channel, such as the projected VEGETATION radiometer of the French Space Agency. AVHRR day-time imagery is used in order to simulate this radiometer. An algorithm is written making only use of the first two AVHRR channels, and is called the WSD algorithm. IN order to assess the accuracy of its retrieval of the cloud cover, its results are compared to what is called a reference algorithm which on the contrary makes use of all spectral channels, and is based upon the published work of Saunders and Kriebel. The main originality of the first test of the WSD algorithm is the combination of dynamic thresholding of both reflectance and ratio histograms in an iterative fashion. It increases the efficiency of the cloud screening in the following ways: increase the number of clouds detected, decrease the number of actually clear pixels declared as cloudy, make the detection rather insensitive to predefined values. The WSD algorithm is completed by a thresholding on the local variance of the AVHRR 2 reflectance over the ocean. The study shows that cloud screening within a single AVHRR image is possible over Western Europe with visible only. For this area, visible range is more efficient for screening than thermal infra-red. Over the desertic soils of Niger, this is no longer true and both wavelength ranges are required for cloud filtering. This study was funded by Centre National d'Etudes Spatiales (CNES).