Current Development Status of Satellite-borne Scanning Array for Hyper-multispectral Radiowave Imaging (SAMRAI)

Scanning Array for hyper-Multispectral RAdiowave Imaging (SAMRAI) is a passive interferometric radiometer. 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 has been operating the AMSR series of satellite-borne microwave radiometers for over 30 years, including AMSR3, which was launched in 2025.
However, because the design has remained largely unchanged over this time, various issues have become 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 by 2028. SAMRAI is required to receive natural-origin weak microwave power with high sensitivity over an ultra-wideband range, with an upper frequency limit more than 40 times the lower frequency limit. Furthermore, the microwave power amplified during the reception process must be precisely calibrated to the brightness temperature at the input to the antenna. Developing a new receiver that satisfies all of these requirements posed various challenges, but we have overcome them through design improvements.

Here we present the main design changes made to the SAMRAI ultra-wideband receiver since the start of development in 2021, and the performance improvements achieved through these design changes.