Mars Global Surveyor Thermal Emission Spectrometer: Observations of Earth
J. C. Pearl (NASA/GSFC), P. R. Christensen (Arizona State University)
The Mars Global Surveyor spacecraft was successfully launched on November 7, 1996, to arrive at Mars on September 12, 1997. Two weeks after launch, the Thermal Emission Spectrometer (TES) instrument was turned on for performance characterization tests. The Earth was used as a target object to check the registration of the three focal planes, and to verify the calibration. At the time, the spacecraft was 4.7 million kilometers from Earth, at a position very nearly over Hawaii. The data were calibrated with the procedure to be used in Mars orbit. The spectra confirm the expected instrument performance and radiometric accuracy and precision. After scaling to account for the fact that the Earth filled only 9.3% of the instrument field of view, the results provide the first known full-disk infrared spectra of the Earth, as it might be observed during a search for "extrasolar" planets. Spectral features of carbon dioxide, ozone, and water vapor are readily apparent. The inversion of the central Q-branch for the 15 micrometer band of carbon dioxide indicates a warm stratosphere above a tropopause somewhat colder than 215K. The brightness temperature derived within the 800-1200 wavenumber window is 270K, a reasonable average of the ocean surface, cloud tops, and polar regions in the observed hemisphere.