The nature of the systematic radiometric error in the MGS TES spectra

Several systematic radiometric errors are known to affect the data collected by the Thermal Emission Spectrometer (TES) onboard Mars Global Surveyor (MGS). The time-varying wavenumber dependent error that significantly increased in magnitude as the MGS mission progressed is discussed in detail. This error mostly affects spectra of cold (nighttime and polar caps) surfaces and atmospheric spectra in limb viewing geometry. It is proposed here that the source of the radiometric error is a periodic sampling error of the TES interferograms. A simple model of the error is developed that allows predicting its spectral shape for any viewing geometry based on the observed uncalibrated spectrum. Comparison of the radiometric errors observed in the TES spaceviews and those predicted by the model shows an excellent agreement. Spectral shapes of the errors for nadir and limb spectra are simulated based on representative TES spectra. In nighttime and limb spectra, and in spectra of cold polar regions, these radiometric errors can result in an error of ±3-5 K in the retrieved atmospheric and surface temperatures, and significant errors in retrieved opacities of atmospheric aerosols. The model of the TES radiometric error presented here can be used to improve the accuracy of the TES retrievals and increase scientific return from the MGS mission.