Figure 4: Illustration of the benefit of utilising the synergistic retrieval by altitude, latitude and season. Each panel represents an altitude level, with the given altitude in km given on the left. Within each panel, the y-axis represents latitude, with major ticks every 30°. Data were averaged in bins of 2° latitude and 2° Ls. The retrieved posterior errors are divided by the MCD prior errors, such that values below 1 represent retrievals where the uncertainty has been reduced, and thus the co-located observation has injected additional information into the retrieval process.
The benefits of using two spectral ranges is clearly visible, with more than 55% of all synergy retrievals fulfilling all criteria compared to only 24% for SPICAM/NIR, and 16% for PFS/TIR, effectively demonstrating that the synergy yields more information than separately using the SPICAM or the PFS dataset. For all cases the χ2 is the most restrictive requirement (except for PFS/TIR where the DOF is the most restrictive), while the ANR is the least restrictive. The DOF increase provided by synergy compared to retrievals from single spectral domains is a direct evaluation of how much additional information synergy brings to constrain water vapor distribution. Only the measurements fulfilling all four requirements are considered in the following analysis.