Validation of MOPITT carbon monoxide using ground-based Fourier transform infrared spectrometer data from NDACC

Rebecca R. Buchholz, Merritt N. Deeter, Helen M. Worden, John Gille, David P. Edwards, James W. Hannigan, Nicholas B. Jones, Clare Paton-Walsh, David W. T. Griffith, Dan Smale, John Robinson, Kimberly Strong (+6 others)
2017 Atmospheric Measurement Techniques  
<p><strong>Abstract.</strong> The Measurements of Pollution in the Troposphere (MOPITT) satellite instrument provides the longest continuous dataset of carbon monoxide (CO) from space. We perform the first validation of MOPITT version 6 retrievals using total column CO measurements from ground-based remote-sensing Fourier transform infrared spectrometers (FTSs). Validation uses data recorded at 14 stations, that span a wide range of latitudes (80°<span class="thinspace"></span>N to 78°<span
more » ... n>N to 78°<span class="thinspace"></span>S), in the Network for the Detection of Atmospheric Composition Change (NDACC). MOPITT measurements are spatially co-located with each station, and different vertical sensitivities between instruments are accounted for by using MOPITT averaging kernels (AKs). All three MOPITT retrieval types are analyzed: thermal infrared (TIR-only), joint thermal and near infrared (TIR–NIR), and near infrared (NIR-only). Generally, MOPITT measurements overestimate CO relative to FTS measurements, but the bias is typically less than 10<span class="thinspace"></span>%. Mean bias is 2.4<span class="thinspace"></span>% for TIR-only, 5.1<span class="thinspace"></span>% for TIR–NIR, and 6.5<span class="thinspace"></span>% for NIR-only. The TIR–NIR and NIR-only products consistently produce a larger bias and lower correlation than the TIR-only. Validation performance of MOPITT for TIR-only and TIR–NIR retrievals over land or water scenes is equivalent. The four MOPITT detector element pixels are validated separately to account for their different uncertainty characteristics. Pixel 1 produces the highest standard deviation and lowest correlation for all three MOPITT products. However, for TIR-only and TIR–NIR, the error-weighted average that includes all four pixels often provides the best correlation, indicating compensating pixel biases and well-captured error characteristics. We find that MOPITT bias does not depend on latitude but rather is influenced by the proximity to rapidly changing atmospheric CO. MOPITT bias drift has been bound geographically to within ±0.5<span class="thinspace"></span>%<span class="thinspace"></span>yr<sup>−1</sup> or lower at almost all locations.</p>
doi:10.5194/amt-10-1927-2017 fatcat:yehgfjeltvbvjpyeaqssbxm7z4