FSL and CMDL Collaborating to Evaluate GPS for Climate Studies
Two NOAA Research Laboratories, the Forecast Systems Laboratory and the Climate Monitoring Diagnostic Laboratory, are collaborating to evaluate some uses of GPS in climate studies. FSL installed a GPS receiver at the Mauna Loa Observatory (MLO) this fall for an indefinite period, and has been continuously measuring integrated (total atmospheric column) precipitable water vapor from this site called MLO1 since November 12, 2004. FSL is providing the MLO1 GPS receiver, data collection equipment, and data processing services, while CMDL is providing power, data communications, and the ancillary surface meteorological measurements needed to retrieve water vapor from the total atmospheric delays measured by the GPS receiver. All GPS observations are sent to the National Ocean Service National Geodetic Survey’s Continuously Operating Reference Station program for use in the National Spatial Reference System, geodesy, and high accuracy GPS positioning in navigation.
Initially, data from the NOAA Research instrument will be used in data comparison studies with two other systems. The first is the GroundWinds Lidar developed by Michigan Aerospace Corporation (MAC) and the University of New Hampshire. A facility similar to the one at MLO was built by MAC and UNH at the Mt. Washington Observatory near Bartlett, NH. The GroundWinds Lidar system is designed to detect winds from altitudes of 0.5-20 kilometers, but is very sensitive to absorption and scattering from water vapor in the free atmosphere. The second is a GPS receiver designed for space-based applications by Saab Ericsson Space, who wishes to study water vapor variability at lower latitudes from the ground and see how well a high precision GPS receiver is capable of monitoring horizontal variations in water vapor from a zenith pointing antenna. MLO1 has an omni-directional antenna from which zenith-pointing measurements are produced.
In the long term, we plan to use GPS water vapor observations from MLO for calibration and validation of satellite remote sensing data and for determining long-term changes in the quantity of water vapor in the atmosphere above 600 hPa (approximately 3400 m).
Name: Seth Gutman