Obtaining single path phase delays from GPS double differences

We describe a method for obtaining singlepath phase delays from GPS double differences. The resulting "zem differences" (ZDs) can be used for remote sensing of atmospheric water vapor. The method is demonstrated by simulating and observing atmospheric delay gmdients. and by comparing ZDs with pointed radiometer observations of integrated water vapor along GPS ray paths. In-situ GPS antenna phase center and multi path effect.; are mapped in ZD residuals for a specific site and network. We conclude that ZDs derived from GPS network data show promise for real time sensing of water vapor for use in meteorological modeling and forecasting. rier phase ambiguities. However, since the double differences include observations along 4 different paths (from 2 observation sites to 2 satellites), they are more difficult to interpret than single path delays. In this paper we describe a method for converting double differences into single path phase delays (ZDs). Obtaining Zero Differences from Double Differences Double differencing is widely used to analyze GPS observations. Let ~IA and ~A be observations of satellite-.. I and 2 by receiver A. and +. B and ~B be observations by receiver B. "r)1ese observations can then be combined into single differences (SlAB and ~AB).