Comparison and validation of MODIS infrared and near infrared total precipitable water products

The MODIS MOD07 algorithm uses 12 infrared channels (24, 25, 27-36) to retrieve atmospheric profiles of temperature and moisture, total precipitable water vapour (TPW), total ozone, lifted index, and surface skin temperature. The retrieval algorithm uses clear-sky radiances measured by MODIS over land and ocean for both day and night. The algorithm employs a statistical retrieval with an option for a subsequent nonlinear physical retrieval. The synthetic regression coefficients for the statistical retrieval are derived using a fast radiative transfer model with atmospheric characteristics taken from a dataset of 15,704 global profiles of atmospheric temperature, moisture, and ozone profiles. Radiative transfer calculations provide a temperature-moisture-ozone profile / MODIS radiance pair for use in the statistical regression analysis.

Comparisons of MODIS IR TPW and the Near-IR TPW values are made with ground-based measurements (Water Vapour Radiometer, Radisonsonde and GPS) derived TPW over the SGP ARM site Oklahoma for manually selected clear sky cases between April 2001 and August 2005. The MODIS Near IR TPW products use the method of P. Albert et al., which has been added to the International MODIS Atmospheric Processing Package. (IMAPP) that generated the products for this comparison. MOD07 Terra and Aqua near-real time direct broadcast products (including temperature, lifted index, ozone, and mixing ratio) and comparisons can be found at the web site: (http://cimss.ssec.wisc.edu/modis/mod07).