THE TOMORROW.IO MICROWAVE SOUNDER CONSTELLATION: ACHIEVING FULL ON-ORBIT CAPACITY

S. J. Munchak¹, E. Watson¹, S. Williams¹, W. Blackwell²

¹The Tomorrow Companies, Inc., ²MIT Lincoln Laboratory

In August 2024, the first pair of Tomorrow.io Microwave Sounders (TMS) was launched into a sun-synchronous orbit. Since then, four more launches have placed a total of seven TMS space vehicles into a combination of sun-synchronous and 45-degree inclined orbits, with several additional launches planned from late 2025 into 2027. The intended steady-state capacity of at least 14 operating TMS units will provide global hourly revisit rates, augmenting government-operated satellites in relatively few orbital planes with rapid-revisit observations. These observations enhance short- and medium range weather prediction, precipitation nowcasting, and tropical cyclone monitoring. By mid-2025, the TMS constellation was already providing 2.5-hourly average revisit rates and taking measurements covering over 40% of the Earth in one hour.

TMS is a 6U CubeSat microwave radiometer measuring across 12 channels spanning from 91 to 204 GHz (one W-band window channel, seven F-band temperature channels, and four G-band water vapor sounding channels). The instrument design is adapted from the NASA TROPICS mission, with significant changes made to the F-band radiometer back end, which uses a Digital Intermediate Frequency Processor (DIFP), and the inclusion of an internal calibration target (ICT) consisting of radar-absorbing material and characterized by four embedded thermistors.

TMS data quality has been quantified by comparison simulations from radiosondes and reanalysis fields as well as double differences against reference instruments (ATMS and GMI). Based on these metrics, TMS has improved the calibration accuracy of the F-band channels by a factor of 2-3 compared to TROPICS, with a 20-30% improvement in the W- and G-band channels. However, the most salient metrics derive from actual impact studies on forecasts. For precipitation nowcasting, TMS data can improve the accuracy of precipitation detection by 10-15% for up to 70 minutes post-observation (compared to 20-25% for GMI). For NWP analysis, the per-satellite impact of TMS is about 50% that of ATMS for temperature and winds, and similar for water vapor. These results show that higher total impacts for these applications can be achieved at a much lower cost with the TMS constellation compared to legacy satellites, while still acknowledging the necessity of these satellites as high-quality reference measurements.