Enabling Global Observations of Cloud Ice Particle Size and Water Vapor Sounding to Improve Understanding of the Role of Clouds in Climate and Weather Prediction: Tropospheric Water and Cloud ICE (TWICE) 6U CubeSat Instrument

High-altitude ice clouds, covering more than 50% of the Earth’s surface, are often produced from deep convection events impacting life on Earth, and these clouds strongly affect Earth’s weather and climate. They play a significant role in Earth’s energy balance and hydrologic cycle through their radiative feedback and precipitation effects, and therefore are crucial for life on Earth. However, our knowledge of ice cloud particle sizes is currently limited. No global satellite measurements of ice particle size in weather systems are available to observe variations in terms of season or climate environment. Only localized in-situ measurements of ice particle sizes are available. Therefore, global measurements of cloud ice particle sizes, along with associated water vapor profiles, in the upper troposphere and lower stratosphere are critically needed to improve knowledge of the role of ice clouds in Earth’s climate, precipitation and cloud processes. Such observations will enable improvements in cloud and moisture distribution models, as well as in precipitation forecasting. Measurements at a range of frequencies in the millimeter- and sub-millimeter wave frequency range from approximately 200 to 900 GHz provide sensitivity to cloud ice particles in the range of approximately 25 to 100 micrometers.

The Tropospheric Water and Cloud ICE (TWICE) instrument has been developed to provide global observations of upper tropospheric water vapor and ice particle sizes in clouds and their variation with season and climate environment. TWICE is a wide-band millimeter- and sub-millimeter wave radiometer measuring at 16 frequencies in 7 frequency bands from 118 GHz to 850 GHz. The TWICE instrument development was led by Colorado State University (CSU) in partnership with the NASA/Caltech Jet Propulsion Laboratory (JPL) and Northrop Grumman Corporation (NGC). TWICE uses 25-nm InP High Electron Mobility Transistor (HEMT) low-noise amplifier-based (LNA) front-ends operating from 230 to 880 GHz and integrated into single-module receivers from input feed horn to output post-detection voltage. The amplifier front-end and direct-detection architecture provides low noise operation at these sub-millimeter wave frequencies, as well as dramatically reducing the power required, as compared to traditional mixer-based heterodyne architectures. The TWICE radiometers perform end-to-end calibration once each scan by viewing both cold space (2.7 K) reflector and an ambient calibration target at a precisely known thermodynamic temperature. TWICE is capable of operating in a 6U CubeSat, with dimensions of up to 34 cm x 20 cm x 10 cm and mass of up to 12 kg. TWICE can easily be adapted for high-altitude aircraft operation to raise the instrument to TRL 6 and to provide observations for model validation. Finally, the TWICE instrument is adaptable for other small satellite form factors in combination with complementary instruments, including millimeter-wave radar for clouds and precipitation, to enhance its capability to perform measurements for climate prediction and weather forecasting.