The Terra/MOPITT mission: current and future products for carbon monoxide

The Measurements of Pollution in the Troposphere (MOPITT) instrument on the Earth Observing System Terra platform has now acquired more than ten years of global carbon monoxide (CO) observations, forming the longest satellite record for this important pollutant. MOPITT products are routinely exploited to analyze natural and anthropogenic sources of CO, their variability, chemistry-climate coupling and long-range transport of pollution.

MOPITT is uniquely equipped with both thermal-infrared (TIR) and near-infrared (NIR) gas correlation radiometers which together should allow the retrieval of surface-level CO concentrations. Until recently, however, complex geophysical noise processes affecting the NIR radiances prevented their use in MOPITT retrieval products. Thus, the current MOPITT 'Version 4' product exploits the TIR radiances only, which are primarily sensitive to CO in the mid troposphere.

Recently, our understanding of geophysical noise processes has significantly advanced. Sub-pixel variability of the surface reflectance, which varies greatly from observation to observation, results in random radiance errors typically greater than the pure instrumental noise. Sparsely distributed clouds may also effectively increase noise. MOPITT retrieval algorithms have been adapted to better quantify these radiance errors in the production of NIR and joint TIR/NIR retrieval products. These experimental products exhibit substantially improved sensitivity to surface-level CO and will serve as the basis for future operational MOPITT products. Future products will also incorporate corrections for long-term instrumental degradation, which is believed to cause long-term drift in the current operational retrieval products.