Biogenic soil crust affecting satellite spectral response : abstract

1996

Colloque

Karnieli A.

Escadafal Richard (ed.), Mulders M.A. (ed.), Thiombiano L. (ed.) Surveillance des sols dans l'environnement par télédétection et systèmes d'information géographiques = Monitoring soils in the environment with remote sensing and GIS

Paris : ORSTOM, 1996, p. 597 (Colloques et Séminaires). ISBN 2-7099-1331-3 ISSN 0767-2896

Surveillance des Sols dans l'Environnement par Télédétection et Systèmes d'Information Géographiques : Symposium International AISS (Groupes de Travail RS : Télédétection et Cartographie des Sols et DM : Carte Internationale Numérique des Sols et des Terrains) = Monitoring Soils in the Environment with Remote Sensing and GIS : ISSS International Symposium (Working Groups RS and DM), Ouagadougou (BKF), 1995/02/06-10

For the last 20 years, a large number of scientific and technical efforts have been conducted in studying the vegetation patterns and dynamics in the desert transition zone, especially in North Africa. This study suggests a new interpretation for the vegetation remote sensing signal in arid and semi-arid zones. The study is dealing with the effect of biogenic soil crust, which consist of mosses, lichens, algae and cyanobacteria, on satellite spectral reflectance. It was found that : under arid and semi-arid conditions where natural higher vegetation is sparse and covers less than 30% of the surface, the photosynthetic signal in the satellite images is caused mainly by non-vascular plants ; a slight photosynthetic signal exists when the microphytic crusts are dry but a notable signal occurs when they are wet. When wet, the NDVI value can rise up to 30%, although no photosynthetic activity of higher plants is observes ; although the new vegetation indices, such as SAVI and MVI, are supposed to overcome NDVI's limitations, and especially the soil brightness background effect, it was found that all the vegetation indices will be affected similarly by the microphytic crust ; the microphytes are active mainly after rain and flood events. They are observed at the beginning of the rainy season when the annuals are still dy and the perennials have not yet budded. Furthermore, they are also active in the dry seasons after dew nights. Consequently, microphytes activity can affect the interpretation of the VIs during both wet and dry season. The current cloud screening procedures may lead to a misinterpretation of the NDVI since they are base on the highest NDVI value during the entire compositing period ; the higher spectral signal from microphytes crusts occurs across the desert transition zone. (Résumé d'auteur)

Végétation / Forêt [126TELAPP08]

TELEDETECTION SPATIALE ; DONNEES SATELLITE ; ANALYSE SPECTRALE ; REFLECTANCE ; COUVERT VEGETAL

Fonds IRD [F A010008389]

fdi:010008438