Abstract
The Tropospheric Emissions: Monitoring of Pollution (TEMPO) was selected in late 2012 as the first cost-capped and schedule constrained project for Earth Venture Instrument (EVI-1). Launched in April 2023 aboard the Intelsat (now SES) IS40E satellite, it is the first space-borne hyperspectral imaging spectrograph measuring backscattered sunlight over North America in a geostationary orbit (91 West longitude). It serves as the de facto North American element of the atmospheric composition – virtual constellation geo-ring. The instrument’s focal plane has two charge-coupled device (CCD) detectors covering the spectral ranges 293–494 and 538–741 nm with resolutions of 0.53–0.63 nm. It was designed and built to record spectra capable of identifying absorption features of key trace gases important for tropospheric air quality, including ozone, nitrogen dioxide, formaldehyde, and others species. By means of a step-and-stare 2-axis scanning mechanism, nominally once an hour during daylight the TEMPO instrument measures backscattered Earth radiance spectra from the Atlantic to the Pacific Oceans and Mexico City to the Canadian Tar sands. Focused observations over a more restricted East-West region allow shorter revisit times supporting a variety of science and calibration scenarios. Scans during twilight are also possible when permitted within instrument safety constraints. Two transmissive diffusers are used to measure Solar irradiance at weekly and quarterly intervals. Observations of the Sunlit moon have also been recorded. Presented here is the status of the TEMPO radiometric and spectral calibrations for Solar irradiance and Earth radiance spectra. Discussion includes the route taken for combining pre-launch instrument characterization and in-flight data to arrive at the current state and plans for future improvements of the calibration.
TEMPO Calibration Status and the Path Thus Far
The Tropospheric Emissions: Monitoring of Pollution (TEMPO) was selected in late 2012 as the first cost-capped and schedule constrained project for Earth Venture Instrument (EVI-1). Launched in April 2023 aboard the Intelsat (now SES) IS40E satellite, it is the first space-borne hyperspectral imaging spectrograph measuring backscattered sunlight over North America in a geostationary orbit (91 West longitude). It serves as the de facto North American element of the atmospheric composition – virtual constellation geo-ring. The instrument’s focal plane has two charge-coupled device (CCD) detectors covering the spectral ranges 293–494 and 538–741 nm with resolutions of 0.53–0.63 nm. It was designed and built to record spectra capable of identifying absorption features of key trace gases important for tropospheric air quality, including ozone, nitrogen dioxide, formaldehyde, and others species. By means of a step-and-stare 2-axis scanning mechanism, nominally once an hour during daylight the TEMPO instrument measures backscattered Earth radiance spectra from the Atlantic to the Pacific Oceans and Mexico City to the Canadian Tar sands. Focused observations over a more restricted East-West region allow shorter revisit times supporting a variety of science and calibration scenarios. Scans during twilight are also possible when permitted within instrument safety constraints. Two transmissive diffusers are used to measure Solar irradiance at weekly and quarterly intervals. Observations of the Sunlit moon have also been recorded. Presented here is the status of the TEMPO radiometric and spectral calibrations for Solar irradiance and Earth radiance spectra. Discussion includes the route taken for combining pre-launch instrument characterization and in-flight data to arrive at the current state and plans for future improvements of the calibration.