Steps towards evaluating the cost-benefit of observing systems

Quantitative evaluation of the impacts of observations in Numerical Weather Prediction models is an increasingly important requirement for meteorological services. The adjoint-based Forecast Sensitivity to Observations (FSO) is a powerful tool for assessing observation impacts. FSO impacts represent individual observations' contributions to forecast error reduction, and can be combined to assess the relative impact of whole observing networks in an objective manner.

A useful variable we can derive from this is the ‘impact per cost' of observing systems – the average impact of an observation type divided by the overall cost of the network (for a chosen time period). Comparisons of ‘impact per cost' have clear potential to provide evidence to inform network business cases, and act as a step towards representing the cost-benefit of observing systems.

In this work, we suggest appropriate methods of representing the ‘impact per cost' of observing networks, starting with analysis of their impact upon Met Office (UK) 24-hour global forecasts. Where appropriate, we use these methods to evaluate and compare land surface, marine, radiosonde, wind profiler, aircraft and satellite observations. We discuss the intricacies of the FSO tool, and therefore the possible pitfalls in the interpretation of results, and provide insight into their proper interpretation and potential applications. Finally, we consider how this analysis could be extended in order to achieve a fuller representation of the cost-benefit of observing networks.