Surface Biology and Geology (SBG) Visible to Short Wavelength Infrared (VSWIR) Wide Swath Instrument Concept

The 2017 Decadal Survey: Thriving on Our Changing Planet, A Decadal Strategy for Earth Observation from Space has called new observations including global coverage Visible to Short Wavelength Infrared (VSWIR) Wide Swath (WS) imaging spectroscopy measurements as part of the Surface Biology and Geology (SBG) Designated Observable. The SBG VSWIR-WS along with the companion SBG Thermal Infrared (TIR) imager is an important element of NASA's larger Earth System Observatory (ESO). To support NASA and the science and applications community, a concept for a technologically mature VSWIR-WS measurement approach has been developed that takes advantage of previous investments, capabilities of industry, and capabilities of other partners. This concept delivers a 185 km cross-track swath with 30-meter spatial sampling measuring spectra from 360 to 2500 nm with contiguous 10 nm spectral sampling. The system uses an optically fast (F/1.8) telescope with a matched pair of high throughput VSWIR Dyson spectrometers, each covering 92.5 km of the swath. State-of-the-art digital-out detector arrays, one in each spectrometer, are used to provide low-noise and high quantum efficiency over the full VSWIR spectral range. Analysis of the concept performance shows that it delivers excellent cross-track spectral uniformity as well as uniformity through the full wavelength range for each spatial sample. This high fidelity performance is needed to spectroscopically derive consistent global maps of the surface properties that are required to address the objectives described in the SBG science and applications traceability matrix (https://sbg.jpl.nasa.gov/satm). The large concave efficiency tuned electron beam lithography fabricated reflection grating is optimized for high signal-to-noise ratio performance across the spectral range, especially in the visible to support the coastal and inland water objectives. With a nominal polar sun-synchronous orbit, this VSWIR-WS concept provides a 16-day revisit with coverage of the global terrestrial surface and designated aquatic regions. This concept takes advantage of key design elements, such as the Dyson spectrometer and digital-out detector array, to control mass, power, and volume. In this paper, we present the performance and design approach for the VSWIS-WS concept that has been refined to support the SBG Designated Observable and address the key research and applications areas of terrestrial and aquatic ecosystems, solid Earth, hydrology, climate, and weather.