Development of a ground-based microwave spectral radiometer - a downsized version of the satellite-mounted 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. In addition, microwave hyperspectral measurement must have new possibilities, such as making it possible to measure the frequency characteristics of the emissivity of the Earth surface.

Development of the satellite-borne SAMRAI is progressing toward launch in 2027. On the other hand, as the microwave spectrum from the Earth surface will be observed from a satellite for the first time in the world, pre-launch calibration and validation activities are more important than ever in order to generate geophysical data promptly after the satellite is launched. From this perspective, we have developed a ground-based microwave spectral radiometer using part of the SAMRAI receiver system. This ground-based microwave spectral radiometer is much smaller than SAMRAI and can be easily taken out to various environments for observation, and like SAMRAI, it is capable of measuring microwave spectra at 27 MHz intervals from 1 GHz to 41 GHz.

Here, we presents the technical detail of this ground-based microwave spectral radiometer and its performance confirmation results of the observation experiment in addition to the current status of the satellite-mounted SAMRAI development.