Adv. Space Res. Vol. 7, No. 11, pp. (1l)45—(11)57, 1987 0273—1177/87 $0.00+.50 Printed in Great Britain. All rights reserved. Copyright © 1987 COSPAR PROBLEMS RELATED TO THE DETERMINATION OF LAND SURFACE PARAMETERS AND FLUXES OVER HETEROGENEOUS MEDIA FROM SATELLITE DATA F. Becker* and M. Raffy** * Hydrological Sciences Branch, NASA/Goddard Space Flight Center, Greenbelt, MD, U.S.A. * *LSI7~~/GSTS, ENSPS, 7 rue de 1’ Universite, 67000 Strasbourg, France ABSTRACT Satellites will be important tools for climatological research and observations when the means to determine land surface parameters and fluxes from their radiances become operational. In order to achieve this goal, it is necessary to derive adequate models which relate the fluxes to the measured radiances and to invert these models. However, while this determination is relatively straight—forward for homogeneous media, this is not the case for vegetated areas and heterogeneous surfaces, which make up the IFOV of most satellites. This paper presents a discussion of the problems encountered in the definition of relevant parameters which can describe heterogeneous media as a whole and will tentatively give a procedure to extend the definition of parameters from local to regional scales via inversion of appropriate models. The discussion addresses the adequacy, which appears possible, of these models for describing physical processes at the Earth/atmosphere interface as observed with satellite systems. INTRODUCTION Satellites will be important tools for climatological research and observations when means to determine land surface parameters and fluxes from their radiances become operational. In order to achieve this goal, it is necessary to derive adequate models which relate the fluxes to the measured radiances and to invert these models. For homogeneous surfaces such models have been derived and can estimate thermal inertia, the latent and sensible heat fluxes as well as albedos and radiative fluxes /1—9/. Unfortunately, due to the spatial dimensions of satellite pixels actually used in climatic studies, the soil cannot be considered to be homogeneous within the IFOV /10,11/, leading to a modification of remotely sensed temperature and flux distribution /12/. Therefore, simple extensions of the above—mentioned inversion method to hetero- geneous pixels which occur at satellite scale have to be reexamined. In fact, the impact of such an heterogeneity on satellite radiances and their physical meaning have been looked at by several authors /13—14/. It turns out that these radiances lead to parameters which do not obey exactly the local equations. This implies the derivation of equations valid at regional scales relating newly—defined parameters /14,15/ which could be used in GCM and monitored from satellites. In section 2 we shall discuss the problems raised by the extension of models and para- meters from local to large scales. Research towards relevant models and parameters relevant at large scale will then be presented in section 3. Section 4 will be devoted to the discussion of some quantitative results on particular heterogeneous media. PROBLEMS DUE TO THE HETEROGENEITY OF LAND SURFACE AT VARIOUS SCALES Parameters and Models at a Given Scale All the parameters describing the characteristics of an elementary volume of land and its boundaries as well as the physical processes occuring in this volume and at its *On leave of absence from LSIT/GSTS ENSPS, 7, Rue de l’universite, 67000 Strasbourg, France tLaboratoire Associe au CNRS. (11)45