This paper proposes a method to estimate precipitable water (PW) distribution over land using NOAA Advanced Very High Resolution Radiometer (AVHRR) thermal data, and mapping of daily PW over Japan from 1984 to 2001 were carried out using this method. The method adopts the split-window algorithm which utilizes the differential atmospheric effect in the two thermal wavebands. The brightness temperature difference between AVHRR channel 4 and 5 (denoted as T4-T5) increases along with atmospheric water vapor abundance, scan angle and land surface temperature (LST) . The effect caused by scan angle and LST was simulated using radiative transfer model and the correction formulas to eliminate theses effects from (T4-T5) were developed. The PW estimation formula was derived from the regression analysis between the (T4-T5) and GPS-derived PW. The root-mean-square error of the PW estimation is approximately 6 mm, and our AVHRR-based estimation has a fairly good result compared with that of radiosondes.
