[1] This paper describes how the fringe-washing function of a wide field of view interferometric radiometer can be accurately estimated using a relatively simple method. Fringe washing is an undesired effect that can be avoided in radio-telescopes due to its narrow-beam nature, but which is unavoidable in wide field of view interferometers, as those built for Earth Observation applications. The 3-delay method is based on performing correlations at -T, 0 and ϩT lags of each baseline of the interferometer, when all receiver inputs are connected to a common noise source (centralized correlated noise injection). In addition, a fringe-washing function closure relationship is presented which allows to extend this concept to aperture synthesis radiometers using distributed correlated noise injection. The results presented in this paper are simulations based on real measurements of the end-to-end frequency response of the first prototype receivers of ESA s Microwave Imaging Radiometer with Aperture Synthesis (MIRAS).INDEX TERMS: 6969 Radio Science: Remote sensing; 6994 Radio Science: Instruments and techniques; 6924 Radio Science: Interferometry; KEYWORDS: aperture synthesis, calibration, fringe washing Citation: Butora, R., M. Martín-Neira, and A.-L. Rivada-Antich, Fringe-washing function calibration in aperture synthesis microwave radiometry,

[1] This study deals with the calculation of the distribution of radiometric errors (''noise maps'') in the images formed by a two-dimensional aperture synthesis radiometer, specifically the MIRAS and the HUT-2D instruments. MIRAS is a spaceborne Y-shaped interferometric radiometer that will be boarded in the European Space Agency's SMOS Earth Explorer Mission. The HUT-2D is a U-shaped airborne interferometric radiometer under development by the Helsinki University of Technology. The study focuses on the known fact that the cross-correlation of the visibility noise does depend on the shape of the sensor. We investigate this dependence for the Y and the U configurations, taking into account also the results of previous studies on redundancy and tapering.

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An airborne L-band two-dimensional interferometric radiometer by aperture synthesis, HUT-2D, is under development and construction at LST/HUT (Laboratory of Space Technology / Helsinki University of Technology) in co-operation with Ylinen Electronics Ltd. The instrument consists of 36 antenndreceiver elements and an FPGA-based digital correlator and it will be accommodated onboard the LST/HUT remote sensing aircraft, Short SC-7 Skyvan.

An airborne L-band aperture synthesis radiometer, HUT-2D, is under development in Helsinki University of Technology, Laboratory of Space Technology (HUT/LST) in co-operation with Ylinen Electronics Ltd. The airborne platform for the instrument will be the HUT/LST remote sensing aircraft, Short SC-7 Skyvan. A four-element subassembly has been manufactured and test measurements are in progress to verify the chosen technology.