Impact of the Antenna Spacing on the Brightness Temperature Maps Retrieved with a Synthetic Aperture Imaging Radiometer.

For almost five years, phase 0 and phase A studies have been conducted by the French space agency for a second generation of the Soil Moisture and Ocean Salinity (SMOS) satellite devoted to a High Resolution (HR) follow-on mission. Within the frame of the preliminary results obtained with a candidate array for this SMOS-HR project, this contribution focuses on what could happen to any synthetic aperture imaging radiometer when the shortest spacing between the antennas of the interferometric array becomes smaller than a geometrical limit below which the synthesized field of view seems to be wider than the field of view seen by each elementary antenna. It is shown that in such a situation, the inversion of the complex visibilities becomes unstable in presence of noise and this instability is characterized by the undesirable presence of a phantom in the retrieved brightness temperature maps. The origin of this phantom is explained and a solution to cure the interferometric array from that issue is proposed and assessed with the aid of numerical simulations.