The problems associated with the validation of satellite-derived estimates of the surface fluxes are discussed and the possibility of using the large aperture scintillometer is investigated. Simple models are described to derive surface temperature and sensible heat flux from the advanced very high resolution radiometer (AVHRR). Data were collected over an extensive site of semi-arid grassland in northwest Mexico during the summer of 1997 as part of the semi-arid land-surface-atmosphere (SALSA) program. Comparison of surface temperature derived from AVHRR with that derived from a ground-based infrared thermometer showed an RMSE of around 2oC, while estimates of sensible heat flux derived from AVHRR compared well with measurements using either eddy correlation or a large aperture scintillometer.