GPS sensed small scale water vapor variability in the Southern Great Planes

A network of twenty-four low cost, single-frequency GPS systems has been installed within ten kilometers of the U.S. Department of Energy's Atmospheric Radiation Measurement (ARM) Program's Southern Great Planes central facility. The purpose of this array is to measure the three-dimensional water vapor variability across the network. These variations are observed by measuring the integrated amount of water vapor along the individual ray paths between each GPS satellite and each of the twenty-four GPS systems. These observations are then combined into a single field that describes the water vapor structure above the network.

Each of the systems utilizes a single-frequency GPS receiver combined with a 900 MHz radio modem. The data are continuously streamed back to a single computer where they are collected and transferred each night through the Internet back to Boulder, CO for analysis. Because these systems utilize only one of the two GPS carrier frequencies, the observations can not remove the effect of the ionosphere. We overcome this problem through the use of global ionosphere maps and observations from surrounding dual frequency GPS stations.

This network of GPS receivers is intended to monitor the water vapor field above the network with a spatial resolution of approximately one-kilometer and one millimeter precision in integrated water vapor. The time varying field retrieved from this network of GPS stations will allow for an improved understanding of water vapor in relation to convection initiation, dry-line structure, and boundary layer moisture fields.