ABSTRACT
Thermal images acquired at night are important for mapping frost zones. An example is given for the Rhone valley wherein NOAA-7 data acquired at 3 h 00 TU on 15 and 23 March 1982 were used to detect zones sensitive to frosting. Thermal-infrared remote sensing can furnish information on topoclimate of these regions with high spatial resolution. Microwave remote sensing has been mainly used in moist and cloudy zones in intertropical or temperate regions to compensate for the impossibility of acquiring data in the visible and near infrared bands. A radar unit derived from a military system was used in France for civil purposes only in April 1973. Regions affected by rain show lower surface temperatures due to evapotranspiration whereas zones with lowest rainfall retain high. The successive positions of a real antenna, related to the forward motion of the platform, are considered elementary sources, giving rise to a 'synthetic' antenna.
