Next Generation Spaceborne Doppler Radars for Cloud and Precipitation Studies: Lessons Learned during the NASA AOS Mission Architecture Study

Spaceborne Doppler radar observations are ideal for acquiring cloud and precipitation measurements at a global scale. The coming decade will feature several new space-borne missions including the ESA-JAXA Earth Cloud Aerosol and Radiation Explorer (EarthCARE) mission, the NASA-Investigation of Convective Updrafts (INCUS) mission, and the NASA-Atmosphere Observing System (AOS) mission. In addition, Tomorrow.io, a private weather company targets to launch a constellation of over 30 Ka-band scanning radars in space by 2026. These planned missions are expected to offer unprecedented measurement capabilities, that in many ways will be superior to those available today from suborbital platforms.

The NASA AOS mission specifically focuses on measurements of aerosols, clouds, convection, and precipitation using a variety of instruments in two orbital planes (inclined and polar). A key focus for clouds, convection, and precipitation is the measurement of vertical air motions over a broad range of cloud and precipitation phenomena. This led to the comprehensive evaluation of several innovative radar concepts spanning across three different wavelengths (Ku, Ka, and W band) during the AOS mission concept study. The different radar concepts that were evaluated featured a wide range of fixed (solid) and deployable antenna sizes, different transmitter technologies (from high power EIKs and solid-state power amplifiers), multiple pulse transmit schemes [that included both short unmodulated and long, frequency modulated (chirp) pulses] and different methodologies for achieving high-quality Doppler velocity measurement [from single antenna concepts with high PRF to the Displaced Phase Center Antenna (DPCA) technique].

The different radar concepts were evaluated using state-of-the-art instrument simulators applied to a wide range of numerical model output used to examine the strengths and limitations of each measurement approach in a wide range of cloud, convection, and precipitation conditions. Here, we will provide a summary of the main lessons learned during the NASA AOS mission architecture study regarding the effectiveness of different radar concepts in meeting the need for concurrent radar reflectivity and Doppler velocity measurements. In addition, we will present a preliminary assessment of current options for the AOS polar radar.