TROPICAL DRY ECOSYSTEMS MODELING AND MONITORING FROM SPACE

Most dry ecosystems of the intertropical belt are subjected to anthrop ic pressures and climatic hazard. Many are strongly disturbed. In many cases, understanding their functioning, dynamics, evolution, and fina lly their general state of health, requires repetitive and overall sur veys. In this context remote sensing can become a very powerful tool p rovided we can reliably relate ecosystem characteristics and radiometr ic information from space. Here, our main objective is the extraction of major ecosystem characteristics, in order to monitor tree mortality and beyond to manage reviewable resources. We developed a procedure t o invert the DART (Discrete Anisotropic Radiative Transfer) model. Thi s is well adapted to the environment, because of its capacity of simul ating radiative transfer in heterogeneous 3-D scenes that comprise tre es, shrubs and soil. It simulates spectral bi-directional reflectance images, for any viewing and illumination configuration. We tested the validity of this approach with a set of ten Landsat MSS (Multispectral Scanner System) images acquired during the 1972-1990 period, over a t est site (84 per 43 km) located in east Burkina Faso (West Africa). Av ailable ecosystem characteristics and rainfall data were used. This pa per presents the development of the inversion methodology for retrievi ng ecosystem characteristics directly from multispectral and multidate remotely sensed data. Preliminary results clearly stress the potentia l of remote sensing systems for conducting sound ecological surveys an d the interest of such a model inversion method as a management tool i n sparse vegetation countries where firewood, vital fuel for human soc ieties, becomes lacking. (C) 1998 Elsevier Science B.V. All rights res erved.