Figure 2: Total column-integrated abundance shown as a function of season and latitude. The figure includes all data points in the synergy dataset. Note that no binning or selection has been done, and data points are partially overlapping with more recent observations on top.
Several selection criteria were applied to the PFS and SPICAM measurements when assembling the synergy dataset, yet not all selected retrievals yielded satisfying results. Some data points have a retrieved CIA below 1 pr-μm, which is considered to be below the sensitivity limit of the synergy method, and a few retrievals also have extremely high values that are deemed unlikely to occur, others yield poor fits and high χ2  values.
The aforementioned benefit of an increased DOF by the use of a spectral synergy approach is demonstrated in Figure 3. While water vapor column abundances from all available co-located observations were shown in Figure 2, only data points with a reduced χ2 of the retrieval equal to or smaller than 4 are shown in Figure 3, where the distribution of abundance-to-noise ratios (ANR) and the DOFs for the synergy are shown along with the parameters from SPICAM/NIR and PFS/TIR. Note that the data points are layered according to method, with the higher synergistic values in the far back, and the method providing the lowest average values in the front.