Impacts of updated spectroscopy on thermal infrared retrievals of methane evaluated with HIPPO data

[摘要] Errors in the spectroscopic parameters used in the forward radiativetransfer model can introduce spatially, temporally, and altitude-dependentbiases in trace gas retrievals. For well-mixed trace gases such as methane,where the variability of tropospheric mixing ratios is relatively small,reducing such biases is particularly important. We use aircraft observationsfrom all five missions of the HIAPER Pole-to-Pole Observations (HIPPO) ofthe Carbon Cycle and Greenhouse Gases Study to evaluate the impact ofupdates to spectroscopic parameters for methane (CH₄), water vapor(H₂O), and nitrous oxide (N₂O) on thermal infrared retrievals ofmethane from the NASA Aura Tropospheric Emission Spectrometer (TES). We findthat updates to the spectroscopic parameters for CH₄ result in asubstantially smaller mean bias in the retrieved CH₄ when compared withHIPPO observations. After an N₂O-based correction, the bias in TESmethane upper tropospheric representative values for measurements between50° S and 50° N decreases from 56.9 to 25.7 ppbv,while the bias in the lower tropospheric representative value increases onlyslightly (from 27.3 to 28.4 ppbv). For retrievals with less than 1.6degrees of freedom for signal (DOFS), the bias is reduced from 26.8 to4.8 ppbv. We also find that updates to the spectroscopic parameters forN₂O reduce the errors in the retrieved N₂O profile.

[学科分类] 几何与拓扑