On the relation between HCMM satellite data and temperatures from standard meteorological sites in complex terrain

Data from the Heat Capacity Mapping Mission Experiment Satellite (HCMM) are used to plot lines of constant temperature at 1° intervals for the city of Melbourne and surrounding country. Using four individual scenes, the relationship between uncalibrated, i.e. relative, surface temperature and screen daily minimum air temperature at some 26 standard meteorological stations in the greater Melbourne region was studied. It was found that the relation between the two data sources is poor for the sites taken separately but that means of daily minimum temperatures for appropriately grouped meteorological sites show a consistent linear relationship with night-time HCMM data. The HCMM data also show significant variation in surface temperatures within short distances from meteorological sites and it is concluded that surface temperatures in such an area vary on a spatial scale that is large compared with the area sampled by a standard meteorological site but small compared with an HCMM pixel. The implications are that a number of sites arc needed to characterize a region independently of site-specific effects (i.e. that appropriately grouped sites can under some circumstances be used for calibrating satellite thermal data) and that thermal imagery could provide criteria for the selection of new standard meteorological sites.