The global sea surface salinity (SSS) can be accomplished by means of the L-band microwave radiometers from space, such as European Space Agencys SMOS (Soil Moisture and Ocean Salinity) and NASAs Aquarius/SAC-D. However, the Microwave Imaging Radiometer using Aperture Synthesis (MIRAS) in SMOS mission suffers from various errors and unexpected in-orbit phenomena, which degrade SSS accuracy. To further improve SSS accuracy, a Full Polarization Aperture Synthesis Microwave Radiometer (FPASMR) has been proposed for Chinas next generation Haiyang (HY) satellite program with two important improvements, which is composed by an L-band and X-band aperture synthesis radiometer (ASR) with two dimensions. One important improvement is that the sea surface roughness (SSR) and sea surface temperature (SST) are simultaneously measured by the full polarization X-band ASR, and another important improvement is that the microwave-optical receiving technology and in-orbit thermal control subsystem are employed to improve the stability of the FPASMR for reducing visibility phase errors. The system of the FPASMR is introduced in terms of L-band subsystem, X-band subsystem and the calibration subsystem. The main specifications of the FPASMR are analyzed in terms of field of view (FOV), angular resolution and radiometric sensitivity. In addition, the FPASMR calibration is also introduced. The FPASMR demonstrator has also been developed and a series of experiments is performed to assess the performance of the FPASMR demonstrator and the improvements in the FPASMR.

The effective calibration of systematic errors is a precondition for high-quality images from a synthetic aperture radiometer system. The receiving channel errors can be relatively well calibrated, but antenna errors cannot be calibrated effectively in-orbit. This paper proposes an in-orbit external antenna error calibration method for synthetic aperture radiometers using external calibration point sources on the ground. Simulation and experimental results demonstrate the accuracy and feasibility of the method. The layout of on-ground calibration point sources was then explored. Our results indicate that is sufficient to adjust the power of the calibration point sources when SNR is 30 dB, and that the calibration requirements can initially be met with three calibration point sources. If better calibration effect is required, eight calibration point sources are sufficient. Non-repeated and uniform azimuth angle schemes appear to be the optimal layout for operating the proposed method, but adjustments can be made as necessary to suit the situation at hand. Finally, a feasible implementation scheme was established. The proposed method has certain reference value in terms of image quality improvement and practical engineering applications.