MODIS stands for MODerate resolution Imaging Spectroradiometer. This sensor, equipped with over 30 spectral channels from the visible into the infrared frequency range operates from aboard the EOS-TERRA and EOS-AQUA satellites since 2000 and 2002, respectively. Thanks to its high spectral resolution and the large number of different channels a large number of different atmospheric parameters can be retrieved. Here we refer to the columnar water vapor content and precipitable water content (PWC) data sets.
Similar to the data sets of the MODIS temperature profile data set the water vapor content and PWC data sets are derived by means of a statistical regression analysis. Vertical profiles of temperature, moisture and ozone measured globally by radiosondes are used to compute MODIS infrared band radiances using a radiative transfer / transmission model. A regression analysis between the computed radiances and the measured atmospheric profiles is carried out to derive the regression coefficients. These are subsequently applied to the actual MODIS radiance measurements to retrieve the profiles of atmospheric parameters - here the humidity which is subsequently vertically integrated to obtain estimates of the columnar water vapor content and PWC.
In addition, one can exploit that the degree with which near infrared (NIR) solar radiation reflected at the Earth's surface is absorbed in the atmosphere is a function of the atmospheric water vapor content. Therefore, radiances measured by the 5 MODIS NIR bands centered around the water vapor absorption line at 0.94 µm are used to derive the NIR columnar water vapor content with a look-up table procedure. Elements of the look-up table were pre-calculated using a radiative transfer / transmittance model and a spectroscopic data base.
More information about the data sets can be found on the MODIS-Atmosphere Group webpage and in the references section - here in particular in the article by King et al. (2003).
This is part of the level-3 MOD08/MYD08 data set derived from level-2 MOD05/MYD05 data of the MODIS Collection 6.1 product family, downloaded August 2018.
Last update of data set at ICDC: March 15, 2019