Global map of water vapor content from ADEOS/POLDER and NASA/AERONET

The ADEOS/POLDER sensor provides the first opportunity to measure the atmospheric water vapor content on a global scale. 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 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 is referred to as the two-channel ratio method. It is shown that the global distribution of water vapor content from the POLDER data present the typical characteristics of spatial and temporal changes. 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.