The aim of this study was to explore and consolidate the possible sources of methane (CH₄) biases in retrievals from thermal infrared (TIR) sensors, to establish necessary actions and perform the related work for mitigating biases. The study distinguisged three types of error sources: spectroscopic knowledge and input data to radiative transfer models (RTM), forward model errors, and instrument biases.

For achieving this goal, the study addresses three main objectives, corresponding to three identified tasks:

1. The first objective (covered through Task 1) was to perform an exhaustive analysis of possible error sources, through the review of the relevant literature, of the available experimental data and of the state-of-the-art tools developed for the processing of observational data (obs) and their simulation (calc) in the TIR region, and to derive an assessment and prioritisation of the expected impacts on the CH₄ retrieval from TIR measurements.
2. The second objective (Task 2) was to perform a sensitivity study investigating the impact of these three types of errors on the final CH₄ systematic error, driven by the output of Task 1 assessment and prioritisation. This sensitivity study is reported in this Task 2 Technical note.
3. The third objective (covered by Task 3) defined a work plan and actions for implementing, performing and validating the mitigation of the CH₄ retrieval biases. This was prepared and initiated in the frame of this study, and pursued in follow-on activities.