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Co-rotating Leo satellites for estimating the 2D tropospheric water vapor

The NDSA (Normalized Differential Spectral Absorption) method can be exploited in general to estimate the water vapor content along radio links in the K-Ku bands connecting one pair of satellites. In this paper, we show new results concerning the applicability of the NDSA method to retrieve two-dimensional fields of water vapor by means of a constellation of satellites that rotate in the same orbital plane and along the same angular direction with the same angular speed. The retrieval of two-dimensional water vapor concentration through the NDSA method and this co-rotating satellites geometry approach is evidently ill-conditioned and consequently requires regularization procedures in order to guarantee stable solutions. In this paper, we present new simulation results that show that an inversion based on the Tikhonov estimator is a quite effective way to tackle the problem and to achieve rather reliable reconstructions of the distribution of water vapor.