OCO-3 Instrument

The OCO-3 instrument is built around the OCO-2 flight spare spectrometer assembly. As with OCO-2, OCO-3 does not measure CO₂ or SIF directly. The instrument measures the spectrally-resolved intensity of the reflected sunlight from which CO₂ and SIF are derived.

Three separate spectrometers simultaneously measure the intensity of reflected sunlight across three wavelength bands - CO₂ (at 1.61 um), CO₂ (at 2.06 um) and O₂ (at 0.76um). The absorption levels increase the more of each gas that the sunlight has passed through.

The OCO-3 instrument has an agile two-axis pointing mechanism [Pointing Mirror Assembly (PMA)] that allows for rapid transitions in pointing. The PMA is used to collect Snapshot Area Maps (SAMs) which are data collections over approximately 80km by 80km regions in 2 minutes. These small map-like XCO₂ and SIF datasets are collected to sample emission sources and gradients, areas where plants and crops are being studied, volcanos, and other local carbon sources from space. The PMA also allow for target mode observations, similar to those taken by OCO-2, typically of Total Column Carbon Observation Network (TCCON) ground sites for use in validation.

The OCO spectra must be very accurate. To eliminate energy from other sources that would generate measurement errors, the light detectors (focal plane assembly) for each spectrometer must remain very cold (-120° C or -184° F). A refrigeration device called a cryocooler is used to maintain and control the focal plane temperature.

To Learn More

Read the paper from the OCO team describing the OCO-3 spectrometer and its performance during ground testing before launch. https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2025EA004317