Calibration and Validation of On-Orbit MicroMAS-2A CubeSat Microwave Radiometer

Miniaturized microwave radiometer instruments on CubeSat platforms are now providing quality data that is consistent with larger weather monitoring instruments. Microwave radiometers can obtain all-weather temperature profile measurements, which is key for applications such as studying the rapidly changing inner-core conditions of tropical cyclones. The Micro-Sized Microwave Atmospheric Satellite (MicroMAS-2A) is a 3U CubeSat with a 1U microwave radiometer payload that was launched on January 11, 2018. The MicroMAS-2A payload has ten channels in 4 bands near 90, 118, 183, and 206 GHz for humidity and temperature profiling and precipitation imaging, and provided the first CubeSat microwave atmospheric sounding data from orbit. MicroMAS-2A is a technology demonstration for Time-Resolved Observations of Precipitations structure and storm Intensity with a Constellation of Smallsats (TROPICS), a constellation of six 3U CubeSats that will be launched NET 2020. The TROPICS constellation approach will enable improved temporal and spatial coverage with revisits of less than 1 hour.

In this work, we describe the calibration and validation of MicroMAS-2A on-orbit data. On-orbit calibration correction factors are determined using matchups with the MicroWave Humidity Sounder (MWHS-2) data segments. Both brightness temperature histogram and Monte Carlo-Markov Chain (MCMC) techniques are shown to provide consistent correction factors. Validation is performed by using double difference techniques to compare the MicroMAS-2A data to state-of-the-art Advanced Technology Microwave Sounder (ATMS) data that meet typical criteria, such as within <50 km, clear sky, over water, and as close in time as possible to the MicroMAS-2A data. Both the Rosenkranz Line-by-Line (LBL) Radiative Transfer Model (RTM) and the Community Radiative Transfer Model (CRTM) are used to compute double differences, with atmospheric profile inputs from radiosondes and the Numerical Weather Prediction (NWP) reanalysis dataset ERA5. Our results show double differences of less than 2.5 K for all channels, and as good as <1.0 K for upper atmospheric temperature sounding channels, demonstrating that CubeSat data is comparable to data from operational weather satellites.