Informing the Next Generation of Spaceborne Hyperspectral Microwave Sensors: Introducing the Hyperspectral Microwave Photonic Instrument (HyMPI) and demonstrating its Benefits for the NOAA Mission

Hyperspectral (a few hundred to a few thousand channels) microwave sensors have been strongly advocated by space and meteorological agencies worldwide, to augment Earth's atmospheric sounding capability of temperature, water vapor, and hydrometeors from space (Blackwell et al., 2011; Boukabara et al., 2011; Mahfouf et al., 2015; Aires et al., 2015; Aires et al., 2019). In a 2022 Broad Agency Announcement, the National Oceanic and Atmospheric Administration (NOAA) requested recommendations for a Hyperspectral Microwave Sensor (HyMS) technology concept and a demonstration of its effectiveness to advance operational numerical weather prediction (NWP) from space. The 2021 National Aeronautics and Space Administration (NASA) Planetary Boundary Layer (PBL) Incubation Study Team Report highlighted hyperspectral microwave sensors as an Essential Component to fly in a potential future PBL observing system (Teixeira et al., 2021).

Progress in hyperspectral microwave technology, however, has been very slow due to the numerous technological challenges associated with simultaneously processing an ultra-wide bandwidth at hyperspectral resolution (< 1 GHz), while maintaining a feasible instrument size, weight and power consumption, and cost (SWaP-C). Operational passive microwave space-borne sensors from the current program of record (e.g., the Advanced Atmospheric Microwave Sounder, ATMS), the Time-Resolved Observations of Precipitation structure and storm Intensity with a Constellation of Smallsats (TROPICS) and even planned sensors (e.g., the Microwave Sounder (MWS), the Micro Wave Imager (MWI) and Ice Cloud Imager (ICI)) have only a couple dozen channels, sparsely sampled across the thermal microwave spectrum. This limited number of channels constrains the information content in the measurement to only a few degrees of freedom, limiting vertical resolution and accuracy in the retrieved thermodynamic fields.

Our team at the NASA Goddard Space Flight Center initiated two NASA funded projects aiming to develop core innovative technology that will enable hyperspectral microwave measurements to augment thermodynamic sounding capability of the Earth’s atmosphere from space. The first is an Instrument Incubator Program (IIP) project funded through the Earth Science Technology Office (ESTO) and titled, “Photonic Integrated Circuits (PICs) in Space: The Hyperspectral Microwave Photonic Instrument (HyMPI)”. The second is a Decadal Survey Incubator PBL project titled: ”Hyperspectral Capability for CoSMIR: Enhancing Capability for Future PBL Suborbital Campaigns and Enabling PBL Science from Space”. Our team is also partnering with NOAA through a Broad Agency Announcement to deploy an airborne campaign aimed at collecting hyperspectral microwave measurements from CoSMIR-H and to perform a qualitative and quantitative assessment of the quality of the collected data. We have conducted extensive trade studies to assess the instrument design factors impacting CoSMIR-H and HyMPI temperature, water vapor and hydrometeors retrieval performance (e.g., channel selection, noise equivalent delta temperature (NEDT), to cite a few). Results from these experiments have led to a vision for an intensive field campaign, whose objectives are threefold. We will acquire first-of-a-kind airborne hyperspectral microwave data using CoSMIR-H to: (1) evaluate data quality, (2) perform trade studies to maximize BT information content of atmospheric temperature, water vapor and hydrometeors and demonstrate improved retrieval performance, (3) draw recommendations on future spaceborne HyMS concepts.

Through this work, our team at Goddard Space Flight Center is seeking to establish a partnership with NOAA to co-design the next generation Hyperspectral Microwave Sensor (HyMS) that will meet the observational needs of the NOAA mission.