The project “Towards Unified Error Reporting” (TUNER) aims at providing consistent and intercomparable error estimates for atmospheric temperature and composition measurements from space. Currently multiple retrieval methods are used by the different instrument groups, and along with this various approaches to error estimation are applied. Resulting errors are not always intercomparable. Some kinds of uncertainties are sometimes not reported at all. The different altitude resolutions and the different content of prior information in the data products is a particular problem.
Current scientific activities with satellite Earth observation data have a strong focus on validation and merging of data sets. The construction of long-term satellite data time series is of particular interest in the context of climate change. For all these satellite-data based activities the reliable characterization of the data in terms of uncertainties, altitude resolution, content of a priori information and error covariances is essential. While concepts exist to solve these problems in theory, these are only applicable to a subset of the algorithms used by the various groups.
Instead of dreaming of being provided with the perfect rigorous error estimates by all groups, it seems more adequate to face the fact that for some processors the rigorous error estimates cannot be provided and workarounds have to be developed instead. These include: calibration of the error estimates to each other in order to make them inter-comparable; assessment of altitude resolutions where no averaging kernels are provided; estimation of systematic or parameter errors for data sets where they are not routinely provided; and development of recipes to make retrieval errors comparable for instruments with different altitude resolutions.
The success of this project depends on the participation of representatives from each retrieval group in order to have first hand information about algorithms and corresponding metadata and to make sure that the recommendations developed in the frame of this project will be finally accepted by the respective groups.