Cartographie de l’érosion hydrique en zone montagneuse : cas du bassin versant des Aït Bou Goumez, Haut Atlas, Maroc

Ce travail présente la cartographie de l’érosion hydrique en zones montagneuses (Haute Atlas, Maroc) en se basant sur trois facteurs principaux : la friabilité du substratum rocheux, le degré de pente et la densité du couvert végétal. La carte du potentiel érosif est obtenue par la somme d’indices attribués aux couches thématiques (la friabilité du substratum rocheux, le degré de la pente et la densité du couvert végétal) multipliés par le pourcentage de contribution de chaque facteur. Dans un environnement de SIG, les pourcentages de contribution ont été obtenus par itération en se référant à la réalité de terrain. Les pourcentages 50%, 30% et 20% retenus correspondent respectivement à la friabilité du substratum, le degré de la pente et la densité du couvert végétal. Ce travail peut être utilisé pour cartographier le potentiel érosif dans d’autres bassins versant du Haut Atlas central qui présentent des faciès géologiques, une topographie et un couvert végétal similaires à la zone des Aït Bou Goumez.El objetivo de este trabajo es la realizacion de la cartografía de erosión hídrica en zonas montañosas (Alto Atlas, Marruecos), basándose sobre tres principales factores: la friabilidad del sustrato litológico, el buzamiento y la densidad de la coberteza vegetal. El mapa del potencial erosivo se obtiene por la suma de índices relativos a las capas temáticas (la friabilidad del sustrato litológico, el buzamiento y la densidad de la coberteza vegeta) multiplicado por los porcentajes de contribución de cada factor. Estos porcentajes se han obtenido por iteración refériéndose a la realidad del terreno. Los porcentajes 50%, 30% y 20% retenidos corresponden respectivamente a la friabilidad del sustrato litológico, el buzamiento y la densidad de la coberteza vegetal. Este trabajo puede ser utilizado para cartografiar el potencial erosivo en otras cuencas de drenaje del Alto Atlas central que presentan facies geológicas, topografía y coberteza vegetal similares a la zona de Aït Bou Goumez

Soil Backgrounds Impact Analysis on Chlorophyll Indices Using Field, Airborne and Satellite Hyperspectral Data

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Effects de la couleur et de la brillance du sol les indices de vegetation

Variations in the spectral properties of soils related to their colour and brightness considerably influence the detection of sparse vegetation in heterogeneous environments using vegetation indices. During the last decade, a new generation of vegetation indices (NDVI, PVI, SAVI, MSAVI, TSAVI, TSARVI, ARVI, GEMI, and AVI) was developed in order to minimize these effects. To evaluate the sensitivity of these indices to soil colour and brightness and to test their potential for a more precise description of the vegetation cover for different cover rates, a number of simulations were carried out using a first order radiative transfer model. The model was adapted for studying directly the contribution of the optical properties of bare soils on the vegetation index. The results show that the first order radiative transfer model constitutes a valuable tool for analysing and understanding the interactions between the electromagnetic radiation, the vegetation cover and bare soil. It makes it possible to analyse the effect of colour and brightness on the reflectance factor and, consequently, on the vegetation index. The GEMI, AVI, NDVI, ARVI and PVI indices show lower performance for the management of sparse or moderately dense vegetation environments. They are marked by non-negligible errors related to the optical properties of bare soils. The AVI leads to results that do not reflect the theoretical behaviour of vegetation indices. As to the TSAVI, TSARVI, SAVI and MSAVI indices, they are more resistant to changes in the optical properties of soils and permit better discrimination between the vegetation from the bare soil background in an heterogeneous and relatively complex environment

A review of vegetation indices

In the field of remote sensing applications, scientists have developed vegetation indices (VI) for qualitatively and quantitatively evaluating vegetative covers using spectral measurements. The spectral response of vegetated areas presents a complex mixture of vegetation, soil brightness, environmental effects, shadow, soil color and moisture. Moreover, the VI is affected by spatial-temporal variations of the atmosphere. Over forty vegetation indices have been developed during the last two decades in order to enhance vegetation response and minimize the effects of the factors described above. This paper summarizes, refers and discusses most of the vegetation indices found in the literature. It presents different existing classifications of indices and proposes to group them in a new classification. -Author