Algorithm Theoretical Basis for Version 3 TEMPO Level 0–1 Processor

Abstract The Tropospheric Emissions: Monitoring of Pollution (TEMPO) instrument is the first spaceborne hyperspectral spectrometer that measures backscattered sunlight over North America in a geostationary orbit. The two charge‐coupled device (CCD) detectors of TEMPO, with spectral coverages of 293–494 and 538–741 nm and resolutions of 0.53–0.63 nm, are capable of identifying absorption features of key trace gases, including ozone, nitrogen dioxide, formaldehyde, and others. Using a step‐and‐stare scanning mechanism, the TEMPO instrument measures backscattered Earth radiance spectra hourly during the middle of the day (nominal scans) and every 40 min in the early morning and late afternoon (optimized scans) to effectively cover the sunlit portions of the continent, with scans during twilight when permitted by instrument safety constraints. Solar irradiance measurements are also conducted nominally with a weekly frequency. This article describes the Version 3 algorithm for TEMPO Level 1b data processing, which provides radiometrically and spectrally calibrated solar irradiance and Earth radiance spectra as the primary outputs. The processing includes the conversion of digitized Level‐0 signals to radiance or irradiance, image navigation and registration for Earth spectra, and spectral calibration. This article also discusses calibration key data derived from pre‐launch instrument characterization and in‐flight calibration results.