Observing System Science

GMAO's mission to provide modeling support for NASA's satellite observations encompasses the need to examine the impacts of different observation types in weather and climate prediction. It also requires the ability to simulate potential new observation types, in order to assess their cost benefit, based on their likely impacts on prediction.

Observation Impacts

GMAO has pioneered the evaluation of impacts of satellite observations on weather forecasts. The methodology developed and implemented in GEOS involves use of the adjoint of the entire observing system, which enables quantitative evaluation of the sensitivity of (say) the two-day forecast to different observation types.


When planning new observations that may be used in weather prediction, it is important to assess their likely impacts on the quality of the products. Observing System Simulation Experiments (OSSEs) provide a quantitative means for this. For such OSSEs, GMAO has developed the ability to simulate the entire present-day observing system using output from high-resolution models. It is also possible to synthesize other types of observations that are proposed. Using these simulated observations in the GEOS assimilation system allows for quantitative assessments of the impact of the proposed new dataset in the system, providing key information about the cost benefits of developing new satellite observations.

The OSSE concept is well established for numerical weather prediction. GMAO research is also targeted at developing OSSE concepts for other data types, including proposed measurement to examine air pollution and climate from space.