Global Positioning System (GPS) Promising Measurement Technology for Water Vapor
Recent studies indicate that the GPS may lead to improved short-term weather forecasting models and physical models of cloud formation. Using a network of GPS stations, scientists working with the U.S. Department of Energy’s Atmospheric Radiation Measurement (ARM) program and its partners are developing innovative ways to measure water vapor and tomographic techniques to compute three-dimensional water vapor fields. ARM’s specific interest is gathering information on the formation of clouds.
The new technique depends on a network of GPS receivers, each getting signals from several GPS satellites at once. When a satellite sends a microwave signal through the atmosphere, the signal is delayed by water vapor. Measuring this delay allows scientists to estimate the integrated amount of water vapor along the signal path from the satellite, called the “slant path water vapor.” Analyses provide the variability of water vapor in the space above the GPS receivers as well as the three-dimensional water vapor distribution above the network.
The ARM program and its government and university partners are involved in two related GPS measurement demonstrations. In one project, the University of Oklahoma is partnering with ARM to establish GPS stations over an area of about 55,000 square miles. The second is a collaboration between ARM and the University Corporation for Atmospheric Research to provide a more dense GPS network. If these demonstrations are successful, the projects will show that GPS networks can provide a low cost way to continuously monitor water vapor variability on scales ranging from a few kilometers to 500 kilometers.