An evaluation of slant water vapor using a high resolution numerical weather model [poster]
Braun, J., Ha, S. -Y., Rocken, C., & Kuo, Y. -H. (2004). An evaluation of slant water vapor using a high resolution numerical weather model [poster]. In 14th Atmospheric Radiation Measurement (ARM) Science Team Meeting. Albuquerque, NM, US.
The integral amount of water vapor along a path through the atmosphere is called a measurement of slant water vapor (SW). A ground based GPS station is able to simultaneously measure SW in the direction of all GPS satellites that are visible. A GPS station is typically able to track between six a... Show moreThe integral amount of water vapor along a path through the atmosphere is called a measurement of slant water vapor (SW). A ground based GPS station is able to simultaneously measure SW in the direction of all GPS satellites that are visible. A GPS station is typically able to track between six and twelve satellites at any time, with each satellite having a different elevation and azimuth direction with respect to the station. A previous comparison (Braun et al., 2003) of SW measured both by GPS and a pointing microwave radiometer showed a root mean square difference between the two techniques of 1.3 mm in integrated water vapor. We have investigated the errors associated with GPS derived SW by evaluating how well the standard processing technique was able to retrieve SW from simulated observations created from a high resolution (3 kilometer horizontal resolution) numerical weather model. This simulation depicted the development and movement of a squall line that passed over a large portion of the United States Southern Great Plains region and represents a time period when SW from a network of GPS stations should be more valuable for characterizing the distribution of water vapor in the atmosphere than zenith integrated quantities of water vapor. This simulation provided the opportunity to study realistic systematic and random errors on the technique used to retrieve SW. Using this simulation we have determined that SW provides precise measurements of the spatial variation in water vapor, while sometimes containing systematic errors that affect the accuracy of GPS derived SW. Nevertheless, this simulation illustrates the value of SW measurements in multiple directions when compared to a single zenith integrated quantity. Show less
