Radiation measurements were made during April and May 1986 at M'bour (16.9¿W, 14.3¿N), 80 km south of Dakar, S¿n¿gal. The goal was to derive the optical properties of desert aerosols from ground-based measurements in order to validate satellite monitoring ofthese aerosols. We present here the results of a ground truth experiment. The measurements were performed during 15 nonconsecutive days in April and May 1986. Weather conditions varied during the experiment, as did the aerosol optical thickness (0.4--2 at 550 nm). The results fare consistent with previous studies, notably Shettle's (1984) desert aerosol models; the aerosol characteristics were observed to depend upon the dust conditions, i.e., background or dust conditions. ¿ American Geophysical Union 1988