Development of the MethaneSAT L0-1B processor

MethaneSAT is an Environmental Defense Fund (EDF) satellite mission set to launch in mid-2023 to monitor methane emission from over 80% of the oil and gas industry and other sources with high precision and fine spatial resolution. The MethaneSAT instrument consists of two push-broom imaging spectrometers: the CH4 spectrometer (1.598-1.676 μm) to detect CH4 and CO2 absorption near 1.65 and 1.61 μm, and the O2 spectrometer (1.249-1.305μm) to detect O2 absorption near 1.27 μm. It is currently being built by Ball Aerospace and under sensor-level testing. Integration with the spacecraft bus by Blue Canyon Technologies will occur in Q3 2022 followed by flight-system level testing. MethaneAIR is the airborne simulator for MethaneSAT. It was successfully deployed in July/August 2021 aboard the NSF/NCAR Gulfstream V and produced ~50 hours of observations. A L0-1b processor has been developed for MethaneAIR to convert digital counts to radiometrically, spectrally, and geometrically calibrated L1b radiance spectra.

We will present the details of the L0-1b processor to process nominal radiancemeasurements as well as on-orbit dark, LED, lunar, and airglow measurements. First, image processing steps including various corrections (e.g., gain, nonlinearity, residual image, Pixel Response Non-Uniform (PRNU), Bezel, dark current and straylight), radiometric calibration and noise calculation will be performed to derive radiometrically calibrated data and measurement precision. Then, a wavelength calibration will be conducted to correct wavelength shifts and monitor the changes in Instrument Spectral Response Functions (ISRFs). An orthorectification procedure will be used to geolocate the measurements and calculate viewing geometry with optional GEO-AKAZE to verify geolocation accuracy again reference images and correct for potential errors. Finally, several geolocation related information such as snow/ice and surface types, sun glint will be added. Pixel flagging will be done at various steps. We will also present on-orbit utilities and methods to monitor bad and RTS pixels from dark current measurements, measure detector gains and nonlinearity from LED measurements, trend radiometric calibration and degradation from vicarious calibrations and lunar measurements.