Sounder for Microwave-Based Applications (SMBA): the Next-Gen Backbone Microwave Sounder for the Near Earth Orbit Network

NOAA‘s next-generation low earth orbit (LEO) observing system—the Near Earth Orbit Network (NEON) Program—will include a backbone microwave sounder known as the Sounder for Microwave-Based Applications (SMBA). Current plans call for up to nine SMBA sensors to cover the 2030-2050 timeframe. SMBA sounders will overlap for about a decade with the predecessor Advanced Technology Microwave Sounder (ATMS) sounders on the Joint Polar Satellite System (JPSS) satellites, which are scheduled to be operational through about 2040.

One major difference between JPSS and NEON is that each JPSS satellite manifest includes a copy of each of the different sensors—microwave sounder, IR sounder, visible/IR imager, etc., whereas the NEON sensors will be on “free flyer” smallsat buses. In particular, there is no requirement for the microwave and IR sounders to fly together on the same bus.

At a high-level, SMBA characteristics will be similar to those of existing or earlier microwave sounders. For example, bands of interest include the 18-24 GHz region around the 22.235 GHz resonance, the 50-60 GHz and 118 GHz temperature sounding bands, the 183 GHz humidity sounding band, and window-channel bands around 31-37, 50, 90, 165, and 205-229 GHz. The number of channels within each band, and their bandwidths, etc. can vary depending on the particular sensor design. Potential trade-offs related to the choice of channels and frequencies will be discussed. These can include bandwidth-noise tradeoffs, direct detection vs. heterodyne configuration tradeoffs, interference potential, vertical resolution of the resulting profiles, etc.

The choice of scan geometry (cross-track or conical) is being left to the designer. Noise equivalent delta temperature (NEDT), footprint size, and spatial sampling characteristics are closely related, and the overall sensor performance tradespace will be the subject of Phase A studies commencing in fall 2023. The performance characteristics and their relative priority will be described.

SMBA will include three major new features: the inclusion of hyperspectral capability, a requirement to have radio frequency interference (RFI) detection capability, and SI-traceable inter-calibration. The tradeoffs among these plus the traditional performance parameters and size/weight/power/cost factors is also part of the Phase A studies; examples will be described.