Abstract
In this paper, we deal with the problem of retrieving maps of tropospheric Water Vapor (WV) concentration by means of a set of Low Earth Orbit (LEO) satellites orbiting in the same plane and along the same direction. It is assumed that a number of microwave links is deployed between a group of satellites with microwave transmitters onboard and another group with receivers. It is also assumed that the Normalized Differential Spectral Absorption (NDSA) approach is used to provide time series of Integrated Water Vapor (IWV) along each link. The set of links scans an annular region belonging to the orbital plane of the LEO satellites, so that the time series of the IWV measurements can be exploited to retrieve the WV concentration in such a region. This is a typical tomographic inversion problem. The geometry of the acquisition system and the path-integrated nature of measurements well fit the application of the Exterior Reconstruction Tomographic Algorithm (ERTA), which was proposed several decades ago in contexts different from remote sensing. In this paper, we investigate the potential of ERTA for the WV retrieval and compare its performance with that of a least square inversion approach already presented in the literature. The compared analysis has been carried out through simulations that have highlighted the peculiarities and retrieval capabilities of the two tomographic methods, as well as the impact of the richness of the satellite constellation on the overall performance.
Highlights
It is widely recognized that tropospheric water vapor (WV), which represents about99% of the total WV, is of paramount importance in meteorology [1,2,3,4]
Even though the direct measurements made by radiosondes provide the vertical profiles of WV with good reliability, remote sensing acquisition systems devoted to the estimation of WV on a global scale are of great interest, for instance, for assimilation in numerical weather prediction models
Retrieving the 2D distribution of WV over planes perpendicular to the Earth surface would allow the horizontal structure of the WV fields, which is known in less detail, to be achieved in addition to the vertical profiles
Summary
It is widely recognized that tropospheric water vapor (WV), which represents about. 99% of the total WV, is of paramount importance in meteorology [1,2,3,4]. The unknown 2D field to be retrieved is the WV concentration in the aforementioned annular region of the orbital plane of the LEO satellites while its Radon transform corresponds to the ensemble of IWV estimates made available by the time series of NDSA measurements. The nature of this inversion method—referred to as External.
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