Calibration and Validation for the Surface Biology and Geology (SBG) Mission Concept: Challenges of a Multi-Sensor System for Imaging Spectroscopy and Thermal Imagery

Abstract

The primary objective of the NASA Surface Biology and Geology (SBG) mission is to measure biological, physical, chemical, and mineralogical features of the Earth's surface, realizing the conceptual component of the envisioned NASA Earth System Observatory (ESO). SBG is planned to launch as a two-platform mission in the late 2020s, the first of the ESO satellites. Targeted science and applications objectives based on observations of the Earth's surface biology and geology helped to define the mission architecture and instrument capabilities for the SBG mission concept. These objectives further drove the need for enabling change detection and trending of surface biological and geological features. These needs implied fundamental Journal of Geophysical Research -Biogeosciences calibration goals to achieve the necessary science data quality characteristics. To meet those goals, calibration and validation pre-launch and on-orbit methods formed a basis of the calibration and validation concept, including the combined use of on-board references, vicarious techniques, and routine lunar imaging. International collaboration with space agencies in other countries, an important feature of the recommended SBG mission architecture, uncovered and emphasized the need for inter-calibration techniques that underscored the importance of collaborative instrument characterization data sharing and the use of common calibration references that are International System of Units (SI) traceable in pre-launch and post-launch on orbit calibration mission phases. International collaboration through the use of terrestrial and aquatic networks on six continents for vicarious calibration and validation activities will produce unprecedented data quality. Table 2 Example reference data sets and models, each supporting geometric calibration (Geo Cal), radiometric calibration (Rad Cal), surface reflectance (Reflectance) or the generation of certain science data products (Science Data), with some supporting more than one. Reference Data Set or Model Purpose Star catalog and planetary ephemeris data Geo Cal Leap second and polar wander that includes (UT1-UTC) Geo Cal Ground Control Point (GCP) database or Global Reference Image (GRI) Geo Cal Time-dependent calibration adjustments Rad Cal Lunar irradiance model (e.g., ROLO, GIRO or LIME)* Rad Cal Solar irradiance spectrum* Rad Cal, Reflectance Instrument char. data (e.g., radiometric, spectral and polarization responses) Rad Cal, Reflectance Vicarious calibration adjustments Reflectance Spectral transmission of absorbing gases (e.g., H2O, O3, NO2). Reflectance Meteorological data (e.g., wind, relative humidity, pressure and temperature) Reflectance Aerosol models Reflectance BRDF models of vicarious calibration sites Reflectance Digital Elevation Model (DEM) and Earth Gravitational Model (e.g., EGM96) Geo Cal Inland water body masks or land/water masks Reflectance Land/sea masks Reflectance Bathymetry Reflectance, Science Data Global shoreline vector data set Science Data Sea surface temperature clima...

Designing an Observing System to Study the Surface Biology and Geology (SBG) of the Earth in the 2020s

“…This work provided preliminary analyses to constrain instrument specifications for providing an accuracy at 5% relative uncertainty surface reflectance including dark targets for VSWIR and ≤1°K absolute uncertainty surface temperature for TIR. Using these uncertainty constraints, the Calibration and Validation Working Group provided strategies as additional design constraints based on the ability for instruments to be calibrated: Radiometrically (R), Thermally (T), Spectrally (S), and Geometrically (Turpie et al., 2023). Architecture budgets for mass, power, and volume were then assessed based on their ability to accommodate working group recommended on‐orbit calibration infrastructure elements and ability for lunar calibration and vicarious calibration.…”

Synergies Between NASA's Hyperspectral Aquatic Missions PACE, GLIMR, and SBG: Opportunities for New Science and Applications

“…Historically, aquatic remote sensing instruments require a robust prelaunch characterization and on‐orbit calibration monitoring (McClain et al., 2022). For prelaunch calibration, it is recommended to use similar testing methods and references to maintain consistency across all three missions (Turpie et al., 2023). We can also rely on common references once the instruments are on‐orbit to intercompare for consistency.…”

“…One of the advantages of having three hyperspectral imagers on orbit at the same time is the ability to inter‐compare the missions using the Earth's surface for inter‐calibration or inter‐validation (Turpie et al., 2023). As shown in Figure 3, however, the swaths of PACE and SBG are quite different and it will take time once on orbit to build a data set of coincident clear sky pixels with homogenous conditions over a 1.2 km scale (the OCI cross‐track center pixel size at its 20° tilt) for inter‐comparison.…”

“…Therefore, at‐sensor radiometric calibration inter‐comparison is not possible. Therefore, only surface data products can be intercompared (Turpie et al., 2023). There will likely be opportunities to observe near‐simultaneous, like‐geometry observations between GLIMR and the other two missions, especially where observations are collected frequently, such as over the Gulf of Mexico.…”