Two-dimensional sensitivity analysis of MIPAS observations.

In this paper we propose a new approach to operate two-dimensional sensitivity studies on the observations of MIPAS, an experiment on board the ENVISAT satellite. The proposed analysis system is intended to evaluate the amount and the spatial distribution of the information that is carried by MIPAS observations with respect to the target atmospheric parameters. The new approach enables the definition and assessment of the target-dependent atmospheric sampling of the measurements. The amount of information is evaluated by merging MIPAS measurements, relative to different limb-scans, in a two-dimensional analysis that models the sensitivity of the spectral signals combined with the geometrical redundancy introduced by different observation geometries. The spatial distribution of the information that is obtained with our analysis highlights the advantage of using a two-dimensional retrieval system. Furthermore, within the two-dimensional context, this analysis provides crucial indications for the definition of the optimal retrieval grid and, therefore, for the best exploitation of existing measurements. The proposed analysis is also suited for the design of optimized observation strategies. The sensitivity analysis, applied in this paper to MIPAS observations, can be extended to other orbiting limb sounders that, like MIPAS, continuously measure the atmospheric emission along the orbit track.