Diagnosis of Three-Dimensional Water Vapor Using a GPS Network

In recent years techniques have been developed to obtain integrated water vapor along slant paths between ground-based Global Positioning System (GPS) receivers and the GPS satellites. Results are presented of an observing system simulation (OSS) to determine whether three-dimensional water vapor fields could be recovered from a high-resolution network (e.g., with 40-km spacing) of GPS receivers, in combination with surface moisture observations and a limited number of moisture soundings. The paper describes a three-dimensional variational analysis (3DVAR) that recovers the moisture field from the slant integrated water vapor and other observations. Comparisons between ‘‘nature’’ moisture fields taken from mesoscale models and fields recovered using 3DVAR are presented. It is concluded that a high-resolution network of GPS receivers may allow diagnosis of threedimensional water vapor, with applications for both positioning and mesoscale weather prediction.