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Proceedings Paper

Baseline redundancy in the MIRAS radiometer
Author(s): J. Font-Rossello; Manuel Martin-Neira
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Paper Abstract

The microwave imaging radiometer with aperture synthesis (MIRAS) is an L-band two-dimensional interferometer which the European Space Agency is studying for the global mapping of soil moisture and ocean salinity. The antenna of this instrument has been optimized to reduce the number of receivers and correlators required for the interferometric processing. The antenna is an array of 3 coplanar arms spaced 120 degrees each one with 43 small antenna elements. In addition there is one element at the center of the array and, for calibration purposes, other three in between the arms. The in-phase and quadrature components of the voltage received by each small antenna in the array are correlated with those of any other antenna element. Every cross correlation is a sample of the so called visibility function at the spatial frequency defined by the relative coordinates of the corresponding pair of antenna elements. The brightness temperature distribution is then obtained basically by an inverse Fourier transform of the visibility function. Since more than one antenna pair may have the same baseline coordinates some spatial frequencies of the visibility function are measured more than once. These points of the visibility function are said to be redundant. This paper deals with the redundancy in MIRAS radiometer. The number of redundant points, its distribution in the spatial frequency domain and there the degree of redundancy is first analyzed. Then the correlation between redundant measurements is studied aiming at estimating the improvement in radiometric resolution when redundancies are combined. A trade-off between radiometric resolution gain and increased number of correlators is performed and some conclusions are finally drawn to be applied to the current design of MIRAS digital correlator unit. Passed preliminary results (Ref. 1) show that about 30% of all possible cross correlations correspond to redundancies while the estimated improvement in the radiometric resolution when using them is only of 1%.

Paper Details

Date Published: 31 December 1997
PDF: 11 pages
Proc. SPIE 3221, Sensors, Systems, and Next-Generation Satellites, (31 December 1997); doi: 10.1117/12.298093
Show Author Affiliations
J. Font-Rossello, European Space Agency/ESTEC (Netherlands)
Manuel Martin-Neira, European Space Agency/ESTEC (Netherlands)

Published in SPIE Proceedings Vol. 3221:
Sensors, Systems, and Next-Generation Satellites
Hiroyuki Fujisada, Editor(s)

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