Abstract
The relationship between ground surface temperatures on clear nights in the late frost season and altitudes was analyzed. Data for ground surface temperatures were taken from NOAA/AVHRR infrared channel data (NOAA data) and those for altitudes from the Digital National Land Information of Japan (DNLI). The relationship showed that the hypothetical temperature of a ground surface (θho), if the ground surface would be lowered adiabatically from the altitude of h to 0 m, is calculated from the following equation : θho=θ+A·h/ 100, where θ is the ground surface temperature in °C, h the altitude in m, A the regression coefficient or the lapse rate of ground surface temperature in °C/ 100 m. The hypothetical temperature is defined as the potential temperature of ground surface.
The potential temperature (θho) of a pixel was calculated by the ground surface temperature from NOAA data, the altitude from DNLI, and the regression coefficient (A). Three color images of potential temperature on three clear nights in April to May were drawn. The images showed that the relatively warmer pixels locate in the terrace terrain, the relatively colder pixels in the basin terrain, and that the intermediate temperatures are in the hill slope and the flat terrains. The similarity of the spatial patern of three images implies that the potential temperature of ground surface is an usefull index in assessing the temperature environment of the ground surfaces on clear nights in the late frost season, and for detecting the places which may be susceptible to lower temperatures and/or late frost damage, or which may be of advantage to crop production.
