The Global Positioning System (GPS) satellite constellation was developed for precise navigation and positioning. The GPS today consists of 28 satellites that transmit L-band radio signals. Other global navigation systems are under development and will greatly increase the amount of future satellites. A receiver on the ground can measure with high precision the phase delays of the GPS radio signal caused by the ionosphere and the neutral atmosphere. From these measurements, we can derive total electron content and atmospheric water vapor along the ray path between the GPS satellites and a ground-based receiver. A receiver on board a low-Earth orbiting satellite can provide vertical profiles of electron density, neutral atmosphere bending angles and refractivity. Over the past decade we have witnessed significant progress in the science and technology of both ground-based and space-based atmospheric remote sensing. The ground-based and space-based GPS atmospheric sensing data are expected to have a major impact on climate monitoring, global and regional weather prediction, ionospheric research, and space weather forecasting.

Under the sponsorship of the NSF International Programs, a special field trip was organized to visit key GPS atmospheric remote sensing facilities in Taiwan and Japan for selected U.S. students, during the period of 3 - 14 July 2004. These facilities included the National Space Program Office in Taiwan, the Meteorological Research Institute and the Geological Survey Institute of Japan. This field trip was intended to provide students with an overview from the basic GPS atmospheric measurements to their applications in weather prediction, climate analysis, and ionospheric research.