Proceedings Article | 3 January 2025
KEYWORDS: Microwave radiation, Rain, Ice, Absorption, Troposphere, Thermodynamics, Temporal resolution, Temperature metrology, Surface air temperature, Spatial resolution
New constellations to provide high-resolution atmospheric observations from microwave sounders operating in lowearth orbit are now coming online and are demonstrating the potential to provide operationally useful data. The first of these missions, the NASA TROPICS (Time-Resolved Observations of Precipitation structure and storm Intensity with a Constellation of Smallsats) Earth Venture (EVI-3) mission, was successfully launched into orbit on May 8 and May 25, 2023 (two CubeSats in each of the two launches). TROPICS is now providing nearly all-weather observations of 3-D temperature and humidity, as well as cloud ice and precipitation horizontal structure, at high temporal resolution to conduct high-value science investigations of tropical cyclones. TROPICS is providing rapid-refresh microwave measurements (median refresh rate of better than 60 minutes early in the mission with four functional CubeSats, and now approximately 70-90 minutes with three functional CubeSats) over the tropics that can be used to observe the thermodynamics of the troposphere and precipitation structure for storm systems at the mesoscale and synoptic scale over the entire storm lifecycle. Over 10 Billion observations have been collected thus far by the TROPICS mission, including over 1000 high-resolution images of tropical cyclones, revealing detailed structure of the eyewall and surrounding rain bands. The new 205-GHz channel in particular (together with a traditional channel near 92 GHz) is providing new information on the inner storm structure, and, coupled with the relatively frequent revisit and low downlink latency, is already informing tropical cyclone analysis at operational centers. Four 3U CubeSats (5.4 kg each) for the TROPICS constellation mission were launched into two low-Earth orbital planes inclined at approximately 33 degrees with a 550-km altitude. Each CubeSat comprises a Blue Canyon Technologies bus and a high-performance radiometer payload to provide temperature profiles using seven channels near the 118.75 GHz oxygen absorption line, water vapor profiles using three channels near the 183 GHz water vapor absorption line, imagery in a single channel near 90 GHz for precipitation measurements (when combined with higher resolution water vapor channels), and a single channel at 205 GHz that is more sensitive to precipitation-sized ice particles. TROPICS spatial resolution and measurement sensitivity is comparable with current state-of-the-art observing platforms. Data from the three currently operational CubeSats are downlinked to the ground via the KSAT-Lite and ATLAS Space Operations ground networks with latencies better than one hour. The separate TROPICS Pathfinder mission, which launched into a sun-synchronous orbit on June 30, 2021 in advance of the TROPICS constellation mission, served as a technology demonstration and risk reduction effort. The TROPICS Pathfinder mission, now concluded, yielded useful data for 30+ months of operation and provided an opportunity to checkout and optimize all mission elements prior to the primary constellation mission. TROPICS temperature vertical profile products yield performance slightly worse than ATMS (1.5 K RMS uncertainty for TROPICS versus 1.3 K RMS uncertainty for ATMS averaged from 0-20 km in 3-km layers), and TROPICS water vapor profile products yield performance slightly better than ATMS (19% RMS uncertainty for TROPICS versus 21% uncertainty for ATMS averaged from 0-10 km in 3-km layers). TROPICS rain rate and tropical cyclone intensity products are also available with performance that is on par with that of ATMS. These TROPICS products are now available with much improved median revisit rates and excellent data latencies, enabling their use in operational tropical cyclone forecasting applications.
