CLARREO Observation Modes and Their Impact on Orbit Definition and On-Orbit Operations

The selection of an optimal orbit and definition of acheivable on-orbit operations is critical to CLARREO's ability to produce irrefutable climate records. The foundation of such a product is the use of exacting on-board traceability of the instrument accuracy. Spectral visible and infrared radiances and GPS Radio Occultation (GPSRO) refractivities measured by CLARREO will be used to detect climate trends and to test, validate, and improve climate prediction models. Through a suite of developed computer programs, assessments of the various instrument modes has been performed to choose the orbits in which to place two CLARREO spacecraft, in preparation for a Mission Concept Review. Intercalibration opportunities between CLARREO and other spacecraft making measurements of reflected solar and infra-red radiation has been performed. The tools take into account idealized orbital dynamics of the two spacecraft, and identifies instances in which the measurements from both platforms satisfy temporal, spatial, and solar illumination constraints. In particular, measurements must be obtained within 5 minutes of each other. The difference in the two viewing zenith angles must be within 1 deg. In the case of reflected solar measurements, the difference in the two relative azimuth angles must be within 1 deg, and the solar zenith angle to each spacecraft must be within 75 deg. The software provides time histories of the two gimbal angles and angular speeds needed for the reflected solar instrument to track chosen Earth-fixed targets.