1 Baghdadi N., King C., Bourguignon A., and Remond A., 2002. Potential of ERS and RADARSAT data for surface roughness monitoring over bare agricultural fields : application to catchments in Northern France. International Journal of Remote Sensing, vol. 23, no. 17, pp. 3427-3442. POTENTIAL OF ERS AND RADARSAT DATA FOR SURFACE ROUGHNESS MONITORING OVER BARE AGRICULTURAL FIELDS: APPLICATION TO CATCHMENTS IN NORTHERN FRANCE N. BAGHDADI, C. KING, A. BOURGUIGNON, A. REMOND Bureau de Recherches Géologiques et Minières (BRGM-ARN/MSO) 3 avenue C. Guillemin, B.P. 6009 45060 Orléans cedex 2, France ABSTRACT The potential of synthetic aperture radar (SAR) data for monitoring roughness states over bare agricultural fields has been investigated using one ERS image (23°) and two RADARSAT images (39° and 47°). The relationships between the backscattering coefficient, incidence angle, soil surface roughness and row direction have been examined so as to determine the best SAR configuration for such monitoring. The results indicate a strong dependence of incidence angle on the discrimination between radar return over areas of different surface roughness. At a high incidence angle (47°), the influence of soil roughness on radar return predominates over the influence of other soil parameters, making it possible to discriminate and map various surface roughness classes (smooth, medium and rough) over agricultural fields. Key words: ERS, RADARSAT, soil roughness, incidence angle, soil moisture, row direction. 1. INTRODUCTION In many parts of the world, excess runoff and soil erosion are the major sources of damage in agricultural areas (mudflow, soil loss, erosion, etc.). Surface runoff occurs when rainfall intensity exceeds the soil infiltration capacity (Zobeck and Onstad, 1987; Boiffin et al., 1988; Brun et al., 1990; Le Bissonnais, 1990). As soil roughness plays a role in trapping water, it thus promotes