Estimating the effective wavelength of the thermal band for accurate brightness temperature retrieval: Methods and comparison

Brightness temperature (BT) obtained accurately from the at-sensor radiance observed by thermal remotely sensed imagery is primary but indispensable, especially for sensors provided with just one thermal channel. It is readily to estimate BT by using several empirical constants which were obtained and validated through pre-launch calibration, such as those for Landsat TM/ETM+. Whereas, for some other sensors (e.g. HJ-1B and CBERS-02), of which the calibration results are always unacquirable to the general users. Nevertheless, previous studies indicated that the effective wavelength was a proper solution for this issue. But, the problem is how to estimate the effective wavelength for each specific thermal band, including that of Landsat TM/ETM+, HJ-1B, CBERS-02 and ASTER B13/B14. In this paper, several possible methods were discussed and compared. According to the comparison analysis, an `Iterative´ procedure gave a suitable effective wavelength through which the BT was able to be retrieved precisely. Then, the detailed discussions verified the possibility that using a suitable effective wavelength in BT retrieval procedure, particularly in the case of the pre-launch calibration results are not in hand. Finally, based on our findings, the empirical constants were calculated in order to obtain BT accurately and practicably from the thermal bands of HJ-1B and CBERS-02.