Research and Development of Satellite-borne Scanning Array for Hyper-multispectral Radiowave Imaging (SAMRAI)

Scanning Array for hyper-Multispectral RAdiowave Imaging (SAMRAI) is a passive interferometric radiometer. In this respect, it is similar to MIRAS on board the SMOS satellite launched by ESA, but it realizes ultra-wideband (1-41 GHz) and high-frequency-resolution (27 MHz) microwave spectrum measurement. We believe that SAMRAI is the world's first microwave hyperspectral radiometer. JAXA will continue to operate the satellite-borne microwave radiometer AMSR series for more than 30 years, including AMSR3 currently under development. The design has remained largely unchanged for 30 years, and various issues are becoming apparent. In particular, the radio frequency interference (RFI) contaminating the natural-origin signals is a serious problem, and we believe that microwave hyperspectral measurement is essential for identifying and isolating RFI signals. This was a big motivation for developing SAMRAI. However, microwave hyperspectral measurement must have new possibilities, such as making it possible to measure the frequency characteristics of the emissivity of the Earth surface. SAMRAI's key technologies are:1) ultra-highspeed A/D conversion equivalent to 80 GSPS (SPS : samples per second)2) ultra-wideband antenna (1 - 41 GHz) as an element of a phased array antenna (PAA) system3) on-board data processing for an interferometer using FPGA including mitigation of grating lobes SAMRAI was first developed to be mounted on a helicopter (aircraft-borne SAMRAI), and its performance is currently being confirmed. Based on performance confirmation of the aircraft-borne SAMRAI, the final goal is to develop the satellite-borne SAMRAI and launch it in 2027. Here, we presents the detail of the technical points of SAMRAI, the performance confirmation results of the observation experiment by the aircraft-borne SAMRAI and investigation of a new algorithm for geophysical value retrieval based on microwave spectrum measurement.