Instruments

OCO does not measure CO₂ directly; but rather, the intensity of the sunlight reflected from the presence of CO₂ in a column of air. This measurement is unique like a fingerprint, and can be used for identification. The instruments use a diffraction grating to separate the incoming sunlight into a spectrum of multiple component colors.

The instruments contain three separate spectrometers that simultaneously measure the intensity of reflected sunlight in three wavelength bands - CO₂ (at 1.61 um), CO₂ (at 2.06 um) and O₂ (at 0.76um). The absorption levels indicate the amount of each gas that the sunlight has passed through.

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 a paper from the OCO team describing the OCO-2 spectrometer and its performance shortly after launch. https://amt.copernicus.org/articles/10/59/2017/amt-10-59-2017.pdf

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