A new water vapor algorithm for TRMM Microwave Imager (TMI) measurements based on a log linear relationship

Abstract

A new algorithm is proposed for retrieving atmospheric columnar water vapor (CWV) over ocean in the absence of rain by using the Tropical Rainfall Measuring Mission (TRMM) Microwave Imager (TMI) measurements. Applying a log linear relationship between the brightness temperatures and main environmental variables including CWV, sea surface temperature, wind speed, cloud liquid water path, and cloud temperature, this five‐channel‐based algorithm was developed through radiative transfer model simulations. The unique advantage of this algorithm is that the retrieved CWV, derived simply from only the five channel brightness temperatures without other ancillary data, is hardly influenced by other geophysical variables. Retrievals are compared against radiosonde observations, which showed a good agreement with a bias less than 0.7 kg m−2 and a root mean square error about 2.5 kg m−2, regardless of the presence of clouds. Additionally, comparison is made with CWV retrievals from the Remote Sensing Systems, which showed a high consistency between the two algorithms with a mean difference of 0.021 kg m−2 and a root mean square difference of 2.076 kg m−2. Finally, the similarity of CWV global distributions based on this algorithm to those from other independent data sets suggests that the new algorithm can be applied for climatic applications.