Atmospheric water vapor content from spaceborne POLDER measurements

The POLDER instrument on board ADEOS provides the first opportunity to apply the two-channel ratio technique in the near infrared to retrieve atmospheric water vapor content at the global scale. Over land, POLDER estimates compare well with radiosonde measurements, with a 3.1-kg m/sup -2/ rms error. There is a clear negative bias of a few kg m/sup -2/ however. This bias can be explained by the spectral variation of the target reflectance between the two bands used for the estimate. Over ocean, POLDER estimates compare very well with either radiosonde measurements (6.9 kg m/sup -2/ rms error) or SSM/I estimates (4.2 kg m/sup -2/ rms error). A mapped POLDER product shows a good overall similarity with ECMWF analyzed field, with smaller synoptic structures in the POLDER field. An example of the monthly product is presented.