Recent Advances in Quantitative Precipitation Estimation using Passive Microwave Observations from the Temporal Experiment for Storms and Tropical Systems (TEMPEST)
Authors: Reising Steven C. , Chandrasekar Venkatchalam , Radhakrishnan Chandrasekar , Brown Shannon T. , Gaier Todd C. , Padmanabhan Sharmila 
Published: February 2023

The Temporal Experiment for Storms and Tropical Systems &#8211; Demonstration (TEMPEST-D) mission demonstrated the first global observations from a multi-frequency microwave radiometer on a CubeSat.&#160; The TEMPEST-D CubeSat was deployed from the ISS in July 2018 and operated in low Earth orbit nearly continuously for three years until it re-entered the Earth&#8217;s atmosphere in June 2021. This NASA Earth Venture Technology mission exceeded expectations in terms of scientific data quality, instrument calibration, radiometer stability, and mission duration. TEMPEST-D brightness temperatures were validated using scientific and operational microwave sensors, including GPM/GMI and four MHS sensors on NOAA and ESA/EUMETSAT satellites. These comparison sensors operate at similar frequencies to TEMPEST-D, observing at the 87 GHz window channel, and at 164, 174, 178 and 181 GHz for water vapor sounding, cloud water and precipitation retrievals. TEMPEST-D was shown to have comparable or better performance to much larger operational sensors, in terms of calibration accuracy, precision, stability and instrument noise, during its nearly 3-year mission.TEMPEST-D performed detailed observations of the microphysics of hurricanes, typhoons and tropical cyclones during three consecutive hurricane seasons. Nearly simultaneous observations by TEMPEST-D and JPL&#8217;s RainCube weather radar demonstrated a high degree of correlation between complementary passive and active microwave measurements of convective storms and tropical cyclones from the two CubeSats.&#160; TEMPEST-D periodically performed along-track scanning measurements, providing the first space-borne demonstration of &#8220;hyperspectral&#8221; microwave sounding observations to retrieve the height of the planetary boundary layer with high precision.The highly successful, stable operation of the TEMPEST-D instrument on a 6U CubeSat for nearly three years suggests myriad future opportunities to enhance microwave sounding and imaging of water vapor, clouds and precipitation. During the TEMPEST-D development, a nearly identical TEMPEST sensor was produced for risk reduction. The second sensor was delivered to the U.S. Space Force and integrated with NASA/JPL&#8217;s Compact Ocean Wind Vector Radiometer (COWVR). On December 21, 2021, COWVR and TEMPEST were launched from KSC as part of STP-H8 for 3 years of operations on the ISS. COWVR and TEMPEST-H8 have performed coordinated observations of Earth&#8217;s oceans and atmosphere from the ISS since January 7, 2022. TDRSS allows for near real-time communications from the ISS to ground, and STP-H8 plans to ingest COWVR and TEMPEST microwave observations into short- and medium-term weather forecasting models.Quantitative precipitation estimates from TEMPEST-D on-orbit observations have been produced using a machine-learning approach.&#160; Precipitation retrievals over continental storms as well as land-falling hurricanes demonstrated excellent agreement with multiradar/multisensor system (MRMS) quantitative precipitation estimates (QPE). These retrievals are currently being expanded from CONUS-only to a global basis using the IMERG precipitation dataset.&#160; Similar techniques are being applied to TEMPEST-H8 observations from the ISS to provide retrievals of water vapor profiles, cloud liquid water, cloud ice water, and precipitation.