SENSING ATMOSPHERIC WATER-VAPOR WITH THE GLOBAL POSITIONING SYSTEM

Global Positioning System (GPS) receivers, water vapor radiometers (WV Rs), and surface meteorological equipment were operated at both ends o f a 50-km baseline in colorado to measure the precipitable water vapor (PWV) and wet delay in the line-of-sight to GPS satellites. Using hig h precision orbits, WVR-measured and GPS-inferred PWV differences betw een the two sites usually agreed to better than 1 mm. using less preci se on-line broadcast orbits increased the discrepancy by 30%. Data sim ulations show that GPS measurements can provide mm-level separate PWV estimates for the two sites, as opposed to just their difference, if b aselines exceed 500 km and the highest accuracy GPS orbits are used.