Algorithms for estimation of air-specific humidity using TMI data

We developed two empirical algorithms for estimating the surface air-specific humidity (Q _a) at 10 m over the ocean using Tropical Rainfall Measuring Mission (TRMM) Microwave Imager (TMI) brightness temperature data. We used the in situ data included in the International Comprehensive Ocean-Atmosphere Data Set for 2003–2006 as true values in this study. We estimated the Q _a using the developed regression formulae and validated the results by comparing with moored buoy data. The biases of our product were relatively small, i.e. 0.03 and 0.29 g kg^–1 for TMI_4CH and TMI_9CH, respectively, when compared with other Q _a retrievals. Moreover, we investigated the relationship between the brightness temperature observed by each channel and the in situ Q _a. We concluded that the use of the brightness temperature determined by the 85 GHz polarized radiation can considerably reduce the bias.