Re-calibration of Mars Global Surveyor Thermal Emission Spectrometer spectra. 1. Methodology and re-derived data products: Aerosol opacities and surface emissivities

We describe a new approach to re-calibration of spectra collected by the Thermal Emission Spectrometer (TES) aboard Mars Global Surveyor (MGS) during 1999–2006. Almost a decade after the end of the MGS mission, data collected by MGS TES still constitute an invaluable source for analysis of the Martian atmosphere and surface. However, TES spectra archived with the NASA Planetary Data System (PDS) archive are all affected by a known calibration error. This error manifests itself as non-zero radiance in the spectra of space and negative radiances in the spectra of cold surfaces. This time varying error affects calibration functions and spectra of targets of low intensity, such as Martian nighttime and polar surfaces, and some atmospheric observations. The goal of the re-calibration is to remove this calibration error from the TES calibration functions and from the TES spectra. The calibration error is removed from calibration functions by calculating long-term averages of the TES Instrument Response Function (IRF). The re-calibrated TES spectra are used to re-derive column opacities of atmospheric aerosols, and surface emissivities and related data products, while correcting for the calibration error. The re-calibrated TES spectra and select re-derived data products are now available for download from the Planetary Data Systems (PDS) archive.