Slant-Path Sensing with Ground-Based Global Positioning System (GPS) for Atmospheric Research and Climate Monitoring

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Knowledge of the four dimensional distribution of water vapor is crucial for diagnosis and prediction of the atmosphere. Over the last several years it was discovered that, among other variables, atmospheric moisture affects the propagation of Global Positioning System (GPS) signals in a predictable manner. Currently, microwave signals transmitted by GPS satellites pervade the atmosphere. Refractive delays induced in these signals by the moisture in the atmosphere can be routinely measured and converted into accurate measurements of a vertically integrated quantity known as precipitable water (PW). Under prior support, the Principal Investigators established a university-based GPS system, known as SuomiNet, to measure PW and provide this information to interested users over the Internet for research and education. Under the current award, a powerful augmentation to SuomiNet will be added. The Principal Investigators will develop and validate techniques to determine the slant delay of GPS signals from the satellite to the ground-based receivers. Slant delays can be used to improve high-resolution, three-dimensional water vapor and wind analyses, which is an important step in improving mesoscale modeling and forecasting. The work includes development of slant delay GPS computational methods and assimilation of slant delays into numerical weather models. If successful, the developed techniques will provide much improved resolution of atmospheric variables, which can be used to advance short term forecasting. The SuomiNet receivers will continue to be based primarily at universities and will contribute to local educational efforts in atmospheric measurements.