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Nodal sampling: a new image reconstruction algorithm for SMOS

By Verónica Gonzalez Gambau, Antonio Turiel, Estrella Olmedo Casal, Justino Martinez, Ignasi Corbella Sanahuja and Adriano José Camps Carmona

Abstract

Soil moisture and ocean salinity (SMOS) brightness temperature (TB) images and calibrated visibilities are related by the so-called G -matrix. Due to the incomplete sampling at some spatial frequencies, sharp transitions in the TB scenes generate a Gibbs-like contamination ringing and spread sidelobes. In the current SMOS image reconstruction strategy, a Blackman window is applied to the Fourier components of the TBs to diminish the amplitude of artifacts such as ripples, as well as other Gibbs -like effects. In this paper, a novel image reconstruction algorithm focused on the reduction of Gibbs -like contamination in TB images is proposed. It is based on sampling the TB images at the nodal points, that is, at those points at which the oscillating interference causes the minimum distortion to the geophysical signal. Results show a significant reduction of ripples and sidelobes in strongly radio-frequency interference contaminated images. This technique has been thoroughly validated using snapshots over the ocean, by comparing TBs reconstructed in the standard way or using the nodal sampling (NS) with modeled TBs. Tests have revealed that the standard deviation of the difference between the measurement and the model is reduced around 1 K over clean and stable zones when using NS technique with respect to the SMOS image reconstruction baseline. The reduction is approximately 0.7 K when considering the global ocean. This represents a crucial improvement in TB quality, which will translate in an enhancement of the retrieved geophysical parameters, particularly the sea surface salinity.Peer ReviewedPostprint (author's final draft

Topics: Àrees temàtiques de la UPC::Enginyeria agroalimentària::Ciències de la terra i de la vida, Àrees temàtiques de la UPC::Enginyeria de la telecomunicació::Radiocomunicació i exploració electromagnètica::Teledetecció, Earth sciences, Remote sensing, Image reconstruction, Interferometric radiometer, Nodal points, Nodal sampling (NS), Radio-frequency interferences (RFIs), Sidelobes, Soil moisture and ocean salinity (SMOS), Aperture synthesis radiometry, Interferometric radiometers, Angular resolution, Surface salinity, Ocean, Calibration, Sun, Ciències de la terra, Teledetecció
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Year: 2016
DOI identifier: 10.1109/TGRS.2015.2499324
OAI identifier: oai:upcommons.upc.edu:2117/90880
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