ESRL Global Systems Division

OAR and NESDIS Collaborate to Improve Real-Time Satellite Moisture Observations

NOAA's advancement in weather forecasting and climate prediction depends on its researchers' ability to acquire and analyze vast quantities of environmental data in collaboration with colleagues throughout NOAA and the broader science community. Researchers at the OAR Forecast Systems Laboratory (FSL) in Boulder, CO and the NESDIS Office of Research and Applications (ORA) in Camp Springs, MD are collaborating to use ground-based GPS water vapor sensors to help evaluate and improve GOES satellite atmospheric moisture observations.

Water vapor observations are needed to improve weather forecasts, monitor and predict climate variability, better understand complex physical processes, and verify global weather and climate observations and models. In 1994, FSL collaborated with other NOAA organizations, federal agencies, and universities to establish the world's first GPS network dedicated to atmospheric remote sensing. GPS water vapor sensors complement other NOAA moisture sensing systems such as satellites and radiosondes, because they provide accurate low-cost observations every half hour under all weather conditions. Operational radiosondes make measurements only twice daily at widely spaced locations, and are subject to nonsystematic errors that are difficult to identify under certain circumstances. Satellite infrared measurements are most accurate over land, but they are not reliable under cloudy conditions when, from a forecasting perspective, the need for accurate water vapor information is greatest. As a consequence, GPS water vapor measurements made by FSL are now being used by ORA to assess GOES precipitable water measurements around the clock rather than just twice daily.

To launch the FSL-ORA collaboration, FSL first developed a Web-based tool that automatically compares ground-based GPS water vapor measurements with GOES sounder-derived water vapor data over the continental United States. This software allows GPS water vapor images to be overlaid with GOES water vapor images, as well as visible and infrared images, for comparison. The integration of these observations reveals problems (shown in nonwhite dots) and improves the water values, resulting in more accurate retrievals. ORA scientists use the FSL tool to evaluate the GOES moisture retrieval process and look for ways to improve the estimation of atmospheric moisture (and possibly temperature) from satellite sensors. Though the project has just begun, initial results are very promising. The presence of clouds in the field of view of the satellite sensor can interfere with moisture and temperature retrievals. Developers and researchers can use the tool to see right away if there's a change in the retrieval algorithm or if the data are closer to truth. For example, Gary Gray at NESDIS comments, "GOES retrievals are generally more moist, largely due to several 'outlier' values. This agrees very well with what you guys have reported back and shown to us through all of your excellent work."

The GPS work at FSL is carried out jointly by the Demonstration Division and Forecast Research Division, and is funded in part by GOES-R, GIMPAP, and JCSDA external projects. The GPS contact is Seth Gutman, Chief, GPS-Met Observing Systems Branch at FSL. He can be reached at or 303-497-7031.

Contact information
Name: Daniel L Birkenheuer
Tel: 303-497-5584