ESRL Global Systems Division

Real Improvements in Real-Time Positioning in California

ESRL's Global Systems Division (GSD) has developed a new model, NOAATrop, to improve GPS positioning, navigation, and timing (PNT) accuracy using real-time weather data. NOAATrop uses the ESRL Rapid Update Cycle (RUC) weather prediction model to calculate real-time atmospheric correctors for high-accuracy GPS positioning applications. The California Spatial Reference Center (CSRC) at Scripps Institution of Oceanography recently started using NOAATrop for real-time engineering applications in southern California. This is the first known operational application of a weather model being used to improve high-accuracy GPS surveying. The initial tests in California using NOAATrop as part of a CSRC Height Modernization project, funded by NOAA's National Geodetic Survey (NGS), were very positive, yielding 15-25% improvements in accuracy with the greatest improvements shown in height measurements made during rapidly changing weather conditions. From CSRC's perspective, using NOAATrop increases the accuracy and productivity of field surveys for its user community. Based on CSRC's experience, the NOAATrop model is currently being used in the Central Valley as a way to increase accuracy and productivity of their road and infrastructure surveys.

Background: Scientists involved in using GPS for very high accuracy positioning applications, like the ones at NGS, developed techniques to treat the atmosphere as a source of noise or measurement error and remove it to improve their GPS positioning accuracy. Atmospheric scientists at ESRL's GSD realized that these error estimates told us something very important about the atmosphere and they developed ways to use this "noise" to continuously measure the amount of moisture in the atmosphere. The operational use of this information by NOAA's National Centers for Environmental Prediction has resulted in substantial improvements in U.S. weather forecast accuracy in recent years.

Those GSD scientists soon realized that if they could use GPS data to improve weather forecast accuracy, then an improved weather model could be used in turn to estimate and correct for the atmospheric signal delays that are a major source of GPS PNT error. Several years of independent testing and evaluation around the U.S. by three universities have proven NOAATrop's value in high-accuracy GPS surveying. An immediate application of this tool is in NOAA's height modernization program where significant impacts on accuracy and productivity are expected.

ESRL's GSD is proud to have helped achieve this milestone. We look forward to broader applications of this technology within and outside of NOAA in the future as we continue to support NOAA's mission goal to serve society's needs for Weather and Water information.

Contact information
Name: Seth Gutman
Tel: 303-497-7031