Algorithms for estimation of air-specific humidity using TMI data

Abstract

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.

Acknowledgements

This research was partly funded by the Japan Aerospace Exploration Agency and Tokai University. We would like to thank Remote-Sensing Systems for providing the TMI cloud liquid and rain rate data.