The Westford Water Vapor Experiment: Use of GPS to Determine Total Precipitable Water Vapor

The Westford WAter Vapor Experiment (WWAVE) was designed to measure the temporal and spatial variability of the total precipitable water vapor over an area within a 25 km radius of the Haystack Observatory in Westford, MA. The main experiment was conducted from August 15 to August 30, 1995, and a variety of different techniques were used to measure the water vapor, including: radiosondes, launched two to three times daily from one location; a water vapor radiometer (WVR); eleven GPS receivers separated by 0.5 to 35 km (with 3 receivers located within 1 km of each other at the central location); and 8 surface meteorological monitoring units. In addition, this campaign coincided with the CONT95 VLBI experiment. Thus water vapor retrieval from VLBI is also available for comparison against the other techniques. This paper will focus on the comparison of the total precipitable water vapor measured by radiosondes, water vapor radiometers, and GPS, and will specifically address the accuracy issues of the GPS derived estimate of this quantity.