Calibration Process

The figure below summarizes the calibration parameters that the OCO mission will measure to track instrument degradation using on-orbit tests. The team will transfer the outcome of these studies to the Ancillary Radiometric Product (ARP). The ARP stores both instrument and On Board Calibrator (OBC) descriptive coefficients. A large number of the parameters are based on instrument characterization experiments that the mission will conduct before launch.

Routine updates are required to maintain the accuracy of radiances computed using these coefficients. Thus, the calibration team updates the ARP after each orbit repeat cycle. Each repeat cycle covers 16 days or 233 spacecraft orbits. After the calibration team creates a new file, and the mission approves the file for data production, the OCO Ground Data System will implement the new ARP into the Operational Pipeline process.

The Ground Data System CalApp Product Generation Executive (PGE) will use the approved ARP to generate standard Level 1B Products.

The team will use iterative updates of the ARP to test and modify the algorithms used to produce the radiance parameters. As more data are collected, the calibration team will improve their assessment of:

• the impact of temperature on the variation of detector gain and offset,
• which temperatures correlate best with gain and offset changes,
• which mathematical functions best describe the observables, and
• the need, if any, to correct for stray light on instrument detectors.