Aperture synthesis radiometry is becoming a feasible concept for imaging applications, especially at low microwave frequencies where it takes clear advantage of the absence of mechanical antenna motion. A 2D interferometric radiometer consists of a large number of receivers with small antennas distributed along a 2D structure, and the brightness temperature image is formed by inversion of the measured cross-correlation between all pairs of antennas. This is the concept of MIRAS (MIcrowave Radiometer by Aperture Synthesis), the core instrument of the SMOS (Soil Moisture and Ocean Salinity) mission selected by the European Space Agency (ESA) and planned to be launched in 2005. In its preliminary design, MIRAS receivers are uniformly distributed along a Y-shape structure and work at L-band. This approach, however, poses a challenge in the specifications required for the receivers: a) The short integration time due to the platform motion strongly limits the achievable sensitivity, b) the spatial resolution is determined by the structure dimensions which cannot be made arbitrarily large and c) the radiometric accuracy depends on the non ideal behavior of the receivers, although, to some extent can be corrected by internal calibration. This paper contributes to define the main trade-off between hardware requirements and system performance of this complex instrument.Peer ReviewedPostprint (published version
Since the mid 1980s, aperture synthesis interferometric radiometers have received increased attention to monitor the Earth at low microwave frequencies (L-band), where there is a maximum sensitivity to soil moisture and ocean salinity. At L-band, classic radiometers require large steerable antennas to meet the spatial resolution requirements (30-50 km at most, 10-20 km wished for), from a low polar orbit platform. During the 1990s, technological studies were conducted by the ESA with an eye to design a 2D synthetic aperture L-Band radiometer (the Microwave Imaging Radiometer by Aperture Synthesis project: MIRAS). In 1998, in answer to a call for Earth Explorer Opportunity Missions issued by ESA, the Soil Moisture and Ocean Salinity Mission proposal (SMOS), based upon a radiometer concept derived from the MIRAS studies, was submitted, In 1999, following a selection procedure, ESA approved the SMOS mission for an extended phase. This paper summarize part of the work carried out on the interferometric radiometry concept and the optimization of the instrument configuration.Peer ReviewedPostprint (published version
After more than four years of operation, the SMOS (Soil Moisture and Ocean Salinity) European Space Agency (ESA) mission [1] has proven to be highly useful for a variety of scientific applications related to soil moisture over land and ocean salinity and winds over ocean, as well as specific studies over the ice covered surfaces. Level 2 data is currently used by many institutes around the world to extract relevant information aimed at improving weather forecast, extreme events monitoring and others.Postprint (published version
Since each of the individual elements of the MIRAS array is a total power radiometer, the zero-spacing visibility can be obtained by the average of all the corresponding antenna temperatures. The main advantage of this option with respect to using the NIR measurements is that amplitude calibration is more consistent between zero-spacing visibility and the rest. On the other hand, total power radiometers are not usually as stable as noise injection radiometers, so a small loose of stability could be expected. Preliminary results show, however, similar performance.Peer ReviewedPostprint (author's final draft
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