Retrieval of precipitable water using ADEOS-Ⅱ / GLI near infrared data

[ABSTRACT] Retrieval of vertically integrated water vapor amount (precipitable water) is proposed using near infrared channels of Global Imager onboard Advanced Earth Observing Satellite-Ⅱ (GLI / ADEOS-Ⅱ). The principle of retrieval algorithm is based upon that adopted with Moderate Resolution Imaging Spectroradiometer (MODIS) onboard Earth Observing System (EOS) satellite series. Simulations were carried out with GLI Signal Simulator (GSS) to calculate the radiance ratio between water vapor absorbing bands and non-absorbing bands. As a result, it is found that for the case of high spectral reflectance background (a bright target) such as the land surface, the calibration curves are sensitive to the precipitable water variation. It turns out that aerosol loading has little influence on the retrieval over a bright target for the aerosol optical thickness less than about 1.0 at 500 nm wavelength. A preliminary analysis of GLI data was also carried out and the retrieved result is compared to radiosonde observations. In spite of a lag of several hours between the ADEOS-Ⅱ / GLI and the radiosonde observations, the retrieved precipitable water values were coincident to those of in situ observations within 2.0 mm at a few radiosonde sites. Currently, we are trying to make fully simultaneous comparisons of the retrieved precipitable water values to those derived from continuous observations with skyradiometers or microwave radiometers. As a result, we will validate the accuracy of the retrieval algorithm for the purpose of its global application. It is also anticipated that simultaneous retrieval of the water vapor amount using GLI data along with other channels will lead to improved accuracy of the determination of surface geophysical properties, such as vegetation, ocean color, and snow and ice, through the better atmospheric correction.