Global Observations from a Science-Quality Millimeter-wave Atmospheric Sounding Radiometer on a CubeSat to Improve Weather Forecasting: Temporal Experiment for Storms and Tropical Systems Demonstration (TEMPEST-D)

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 and 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, rapid revisit global observations 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, to improve understanding of the evolution of deep convection and the surrounding water vapor requires fine time-resolution millimeter-wave radiometric observations capable of penetrating deep inside the storm where microphysical precipitation processes occur.

To address this critical observational need, the Temporal Experiment for Storms and Tropical Systems (TEMPEST) mission concept deploys a closely-spaced train of eight 6U CubeSats with 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 and provide water vapor soundings 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, complementing and augmenting existing and future satellite missions, e.g. TROPICS and GPM.

To demonstrate global, well-calibrated radiometric measurements from a 6U CubeSat, the TEMPEST Demonstration (TEMPEST-D) mission was initiated as a partnership among Colorado State University, NASA/Caltech Jet Propulsion Laboratory and Blue Canyon Technologies. The TEMPEST-D satellite was launched on May 21, 2018 on Orbital ATK’s commercial resupply mission to the ISS and was successfully deployed from the ISS on July 13, 2018, from an initial orbit with 400-km altitude and 51.6° inclination.

With more than nine months of operations to date, TEMPEST-D met its mission requirements in the first 90 days. The TEMPEST-D mission has successfully achieved at least TRL 7 for both the instrument and spacecraft systems. TEMPEST-D performed its first full-swath orbital observations on September 11, 2018, capturing Hurricanes Florence, Helene and Isaac over the Atlantic Ocean. TEMPEST-D data are beginning to be used in experiments for data assimilation into NOAA numerical weather prediction models.

TEMPEST-D brightness temperatures have been compared against those of four on-orbit reference sensors, i.e. NASA/JAXA GPM Microwave Imager and Microwave Humidity Sounders on NOAA and EUMETSAT operational meteorological satellites. Results demonstrate agreement between TEMPEST-D radiances and those from reference sensors with a high degree of accuracy and precision. On-orbit results indicate that TEMPEST-D is a very well-calibrated, stable radiometer, indistinguishable in performance from larger, more expensive operational instruments.