Abstract: This paper presents a method for constructing brightness temperature background field based on NOAA/AVHRR thermal datasets in tectonic activity region. We emphatically analyzed some key problems including geometric precision correction, removing the influence of cloud and noise in the process of building background field and the corresponding solution are proposed. On this basis, we established the brightness temperature background field at several scales such as in a period of ten-days, a month and a year in the Capital area of China( 112°～118°E, 38°～42°N ) using NOAA18 thermal infrared images of years. By analyzing the multi-years average background field, we can see that the brightness temperature background field variations are influenced mainly by the season and terrain. In general, the temperature is higher in summer and lower in winter, which agrees with the seasonal changing pattern. And meanwhile it is higher in southeast of north China plain. However, in northwest mountain area, the temperature changes with height contrarily.

Key words: Infrared remote sensing, Brightness temperature, Background field