NOCTURNAL EFFECTS IN THE RETRIEVAL OF LAND-SURFACE TEMPERATURES FROM SATELLITE MEASUREMENTS

The determination of accurate land surface temperatures from infrared satellite measurements is difficult because of variations in atmospheric water vapor and in land surface emissivity. Here we show that under certain conditions (viz. when the atmosphere near the surface is warmer than the surface), there is a cancellation between absorbed and emitted radiation. This often occurs during clear nights when intense nocturnal cooling of the surface causes inversions in the temperature and water vapor profiles. We demonstrate that a reasonable estimate of the land surface temperature can be made from a single channel-infrared measurement in these conditions.