Retrieval of temperature and moisture profiles from AMSU-A and AMSU-B measurements

The NOAA-15 weather satellite carries the Advanced Microwave Sounding Units-A and -B (AMSU-A, AMSU-B) which measure thermal emission from an atmospheric oxygen band, two water lines, and several window frequencies. An iterated minimum-variance algorithm retrieves profiles of temperature and humidity in the atmosphere from this data. Relative humidity is converted into absolute humidity with use of the retrieved temperature profile. Two important issues in the retrieval problem are modeling of the surface and clouds. An a priori surface emissivity is computed on the basis of a preliminary classification, and the surface brightness spectrum is subsequently adjusted simultaneously with the moisture profile retrieval. Cloud liquid water is constrained by a condensation model that uses an extended definition of relative humidity as a parameter.