ESTIMATION OF THE SPATIAL VARIATION OF RAINFALL IN THE SOUTHERN ALPS OF NEW-ZEALAND USING SINGLE-CHANNEL INFRARED SATELLITE IMAGES

The efficacy of low-resolution infrared (IR) satellite data for the es timation of the spatial variation of rainfall is examined. Three analy sis techniques were applied to 41 NOAA satellite images of the Souther n Alps of New Zealand. Estimated rainfall is compared with surface mea surements from 35 sites. Single-channel histograms of cloud-top temper ature are shown to have limited application but demonstrate the diurna l variation of cloud cover. Plots of the fraction of cloud amount belo w four selected temperatures in each of 14 areas across the Alps showe d strong orographic dependence for low and middle cloud. Three simple regression models of rainfall dependence on cloudiness and position al ong a transect crossing the Main Divide show stronger correlation with location than with cloudiness. Spatial-coherence plots identify domin ant clusters of exposed surface or low cloud and indicate the variabil ity of cover at other altitudes.