CPI personnel have developed an innovative, Generalized geophysical Retrieval & ANalysis Tool for planetary atmospheres (GRANT) that facilitates analysis of remote sensing data from both terrestrial and planetary atmospheres. GRANT is based upon a generic and flexible implementation of the optimal estimation inversion technique for atmospheric retrievals (OPT). Its adaptable architecture further provides the user complete flexibility in defining user-configurable forward and sensor models to drive the optimal estimation routine.
The result is a software tool that is easily tailored to a specific sensor and measurement system. It can be used to generate high-fidelity simulated data for testing retrieval algorithm performance and characterizing the resulting data products. Retrieval characterization includes a detailed error analysis package as well as critical diagnostics related to information content, resolution, and model bias.
Beyond the analysis of existing data sets, this tool also provides a powerful capability for rigorously evaluating design decisions on all aspects of future mission development, including sensor design, orbital/flight parameters, and measurement strategies (e.g., viewing geometry, cadence, spectral and spatial sampling).
GRANT is applicable to a wide range of remote sensing missions. It is currently being used operationally, or in the process of being implemented, in the data processing chain for two high-profile NASA science missions. On the MAVEN Mars mission, it is being used to retrieve density profiles of dominant constituents of the Martian atmosphere from analysis of limb radiance profiles measured by the IUVS instrument. In this implementation, the forward model used is CPI’s state-of-the-art FUV-NIR atmospheric radiance model AURIC, as adapted to Mars.
On the upcoming NASA GOLD mission, an FUV imaging spectrograph to be launched in 2017, versions of GRANT and OPT will be used to retrieve exospheric temperature on the limb, effective thermospheric temperature on the disk and thermospheric O2 density profiles from stellar occultation measurements.
Past satellite remote sensing missions for which the GRANT or OPT tools have been used for operational data processing include: POAM II/III (stratospheric trace gasses and aerosols from solar occultation), UARS/SUSIM (thermospheric O2 density from solar occultation), SORCE/SOLSTICE (thermospheric O2 density from stellar occultation), and Coriolis/Windsat (ocean surface wind vector from microwave radiometry).