Estimation of Surface Solar Global Radiation from NOAA AVHRR Data in High Latitudes

A physical method for estimating the instantaneous global irradiance and daily cumulative insolation based on Advanced Very High Resolution Radiometer data was developed and tested at high latitudes in a boreal subarctic region. The satellite estimates were compared with ground-based pyranometer measurements at six stations in Finland. From the comparison of instantaneous satellite estimates with 15-min average irradiances measured by pyranometers, a high correlation coefficient (0.97 in July 1996 and 0.99 in March 1997) between these estimates was obtained under clear-sky conditions. A standard error of 8% and a zero value of bias were obtained in both months. Under cloudy conditions the correlation coefficient in July 1996 was in the range of 0.79–0.83; in March 1997 it ranged from 0.89 to 0.96. The standard error in cloudy cases varied from 27% to 39% in July 1996 and from 17% to 33% in March 1997. For daily insolation estimates, the correlation coefficient had an average value of 0.95. The standard error in clear-sky cases was 7% in July 1996 and 5% in March 1997. In cloudy cases, the standard error varied from 11% to 17% in July 1996 and from 16% to 19% in March 1997. The bias was of opposite sign for the two months, ranging from +7% in July 1996 to −8% in March 1997. The satellite-based daily global radiation spatial distributions were compared in the region of Finland with those obtained by interpolating the station-based pyranometer and visual cloud observations. In southern Finland the estimates of daily global radiation based on interpolated station data and based on satellite data were of equal quality (standard error of about 10%–15%). In northern Finland, where the stations are farther apart, the satellite-based values were much more accurate (standard error of 11%–16%) than were the interpolated estimates from stations (standard error of 43%–74%).