Influence of surface reflectivity variability on MOPITT 2.2-2.3 /spl mu/m channel radiances and the retrieval of CO and CH/sub 4/

The MOPITT (Measurement of Pollution in the Troposphere) instrument uses gas-correlation spectroscopy to retrieve the tropospheric profile of CO and the total column of CO and CH/sub 4/. The instrument's 2.2-2.3 /spl mu/m channel signals can be used to determine the CH/sub 4/ and CO columns. At these wavelengths, surface effects are important since the channel radiances are determined by reflected solar radiation. Small changes in scene during data acquisition for a given pixel can introduce important variations in surface reflectivity, even when averaged over the instrument field-of-view. These variations must be carefully accounted for to ensure a quality column retrieval. MOPITT simulations based on reflectivity measurements from the MODIS Airborne Simulator are used to construct examples illustrating these effects, along with a method for their mitigation.