Title: Global Science-Quality Observations from a Passive Microwave Atmospheric Sounder on a CubeSat: Temporal Experiment for Storms and Tropical Systems Technology Demonstration (TEMPEST-D)
Presenting Author: Steven Reising
Organization: Colorado State University
Co-Author(s): Todd C. Gaier2, Shannon T. Brown2, Sharmila Padmanabhan2, Christian D. Kummerow3, V. Chandrasekar1, Wesley Berg3, Boon H. Lim2, Cate Heneghan2, Richard Schulte3, Yuriy Goncharenko1, Matthew Pallas4, Doug Laczkowski4 and Austin Bullard4 1. Electrical and Computer Engineering Dept., Colorado State University, Fort Collins, CO USA 2. NASA Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA USA 3. Atmospheric Science Dept., Colorado State University, Fort Collins, CO USA 4. Blue Canyon Technologies, Boulder, CO USA

Global observations of clouds and precipitation processes are essential to improve monitoring and prediction of tropical cyclones and severe storms with substantial impacts on human life and property. Convection plays an important role in moving heat in the atmosphere – influencing global weather patterns, distributing fresh water over oceans and land, as well as producing severe weather conditions. However, fundamental gaps remain in understanding the physical processes governing convection, prompting the 2017 Earth Science Decadal Survey to list as one of its "most important" science questions, “Why do convective storms, heavy precipitation, and clouds occur exactly when and where they do?” To understand cloud and precipitation processes in a variety of climate environments, global observations with rapid revisit times are necessary. To this end, geostationary satellites have improved weather prediction by providing visible and infrared measurements with temporal resolution on the order of a few minutes. However, passive microwave measurements provide a greater contribution to forecast skill, due to their capability of penetrating deep inside the storm where the microphysical processes leading to precipitation occur. Therefore, to improve understanding of rapid, dynamic evolution of deep convection and the surrounding water vapor, we require microwave sounding observations with fine temporal resolution necessary to resolve the development of convection. To address this critical observational need, the Temporal Experiment for Storms and Tropical Systems (TEMPEST) mission deploys a closely-spaced train of 6U CubeSats carrying identical low-mass, low-power millimeter-wave radiometers. The TEMPEST train samples rapid changes in convection and water vapor by observing every 3-4 minutes for up to 30 minutes. The millimeter-wave radiometers on TEMPEST observe at five frequencies from 87 to 181 GHz, providing soundings of mid-tropospheric water vapor to improve understanding of its role in the organization and growth of convection. By rapidly sampling the life cycle of convection, TEMPEST fills a critical observational gap and complements existing and future satellite missions, e.g. TROPICS and GPM. To demonstrate global, science-quality radiometric sounding from a 6U CubeSat, the TEMPEST Demonstration (TEMPEST-D) mission was initiated as a partnership among Colorado State University (lead institution and validation), NASA/Caltech Jet Propulsion Laboratory (instrument and calibration) and Blue Canyon Technologies (spacecraft and mission operations). The TEMPEST-D satellite was launched on May 21, 2018 on Orbital ATK’s commercial resupply mission to the ISS and successfully deployed from the ISS by NanoRacks on July 13, 2018, from an initial orbit with 400-km altitude and 51.6 degree inclination to demonstrate that TEMPEST radiometer performance meets the needs of this investigation. With more than six months of operations since spacecraft commissioning, TEMPEST-D has met all mission requirements on schedule and within budget, and continues to acquire global microwave sounding observations. After achieving first light on September 5, 2018, the TEMPEST-D mission has successfully achieved TRL 7 for both the instrument and spacecraft systems. TEMPEST-D performed its first full-swath orbital observations on September 11, 2018, capturing Hurricane Florence over the Atlantic Ocean revealing the eye of the storm surrounded by intense rain bands using millimeter-wave brightness temperatures measured on a CubeSat. TEMPEST-D brightness temperatures have been compared against those of four well-calibrated, on-orbit reference sensors with similar frequencies, i.e. NASA/JAXA GPM Microwave Imager (GMI) and Microwave Humidity Sounders (MHS) on one NOAA and two EUMETSAT operational meteorological satellites. Results demonstrate agreement between TEMPEST-D radiometer measurements and those of the reference sensors, with a high degree of accuracy and precision. On-orbit results indicate that TEMPEST-D is a very well-calibrated and highly stable radiometer with very low noise, rivaling that of much larger, more expensive operational instruments.