Global distribution of atmospheric water vapor

[Abstract] This paper presents a procedure on how to derive the atmospheric water vapor content from ADEOS/POLDER data. A POLDER sensor, mounted on the Earth observation satellite ADEOS in 1996, is a unique sensor which can gather multi-(up to 14) directional polarization measurements of one target. Two channels of POLDER data in the near infrared wavelengths are examined in this study. The first channel is in the water vapor absorption band of 0.910 μm and the second is in the gas absorption-free band of 0.865 μm. In practice, a ratio of each reflectance for these two channels is used to estimate the total column water vapor content. This algorithm will be referred to as the two-channel ratio method. The measured water vapor content from the POLDER data is in close agreement with the ground measurements undertaken at several NASA/AERONET stations. Global distribution of water vapor content presents the typical characteristics of spatial and temporal changes over the whole period of the ADEOS satellite\u27s deployment. The water vapor content has high values over the tropical zone and decreases with latitude. Furthermore, the Indian monsoon is clearly demonstrated in the water vapor map. It should be noted that the water vapor content retrieved from the POLDER data has been validated with AERONET measurements. The global map of water vapor is mutually compared with that of aerosol properties, which are derived from the POLDER polarization data. In addition to the comparison of water vapor content with aerosol loading, it has been found that the WA (water vapor-aerosol) index, i.e. the product of the water vapor content, aerosol optical thickness and Angstrom exponent, is a good indicator to classify the regional characteristics of the atmosphere-surface system. For example, high and low values in the WA index represent a bio-active area and a desert-dust area, respectively.本文データの一部は、CiNiiから複製したものである