Remote sensing of water vapor using GPS receivers

by Quirino Sugon Jr.

I am currently writing a proposal on the use of GPS for water vapor measurements in behalf of Fr. Daniel McNamara, SJ for the Asia Pacific Network.  We have GPS data from our SCINDA and JPL systems at the Manila Observatory, but I have not used them or requested them yet.  Since I know nothing about GPS and water vapor measurements, I surveyed the existing literature.  Below are some useful resources:

Michael Gabor, Remote sensing of water vapor using  GPS receivers (University of Texas, 5 May 1997).

C. Rocken, J. Braun, C. Meertens, R. Ware, S. Sokolovskiy, T. VanHove, “Water Vapor Tomography with Low Cost GPS Receivers,” GPS Research Group, University Corporation For Atmospheric Research, P.O. Box 3000, Boulder CO 80308.  Note: Gabor uses dual frequency data while Rocken et al uses only single frequency data but compensated by an array of receivers.

Michael Bevis, Steven Businger, Thomas A. Herring, Chritian Rocken, Richard A. Anthes, and Randolph H. Ware, “GPS Meteorology: Remote sensing of atmospheric water vapor using the Global Positioning System,” in Journal of Geophysical Research, vol. 97, no. D14, pp. 15787-15801 (Oct 20, 1992). The physics of atmospheric propagation delay is discussed here.  There is also a nice appendix on the ionospheric effects on GPS signals.

J. Braun, T. Van Hove, S. Y. Ha, and C. Rocken, GPS Water Vapor Projects Within the ARM Southern Great Plains Region, Twelfth ARM Science Team Meeting Proceedings, St. Petersburg, Florida, April 8-12, 2002. GPS Science and Technology Program University Corporation for Atmospheric Research, Boulder, Colorado. There is an interesting technology here: slant water vapor (SWV), which is water vapor along the line of site path between a transmitting satellite and a ground-based GPS receiver. I wonder if this is applicable to the SCINDA data.  Btw, there are no equations in the article.

Alexander E. MacDonald*, and Yuanfu Xie*, and Randolph H. Ware**, “Diagnosis of Three-Dimensional Water Vapor Using a GPS Network,” Monthly Weather Review, vol. 130. *Forecast Systems Laboratory, NOAA/OAR, Boulder, Colorado. **GPS Science and Technology Program, University Corporation for Atmospheric Research, Boulder, Colorado. (Manuscript received 26 June 2000, in final form 5 January 2001).  This contains details of the theory behind slant water vapor measurements.  There is no actual network, only a theoretical network.  The meteorological data is simulated using MM5.

SONG Shuli, ZHU Wenyao, DING Jincai, PENG Junhuan, “3D water-vapor tomography with Shanghai GPS network to improve forecasted moisture field,” Chinese Science Bulletin 2006 Vol. 51 No. 5 607—614. DOI: 10.1007/s11434-006-0607-5.  This is an actual GPS network.  The results show promising results.  MM5 model is needed for the background field.

Tobias Nilsson and Lubomir Gradinarsky, “Water Vapor Tomography Using GPS Phase Observations: Simulation Results,” IEEE TRANSACTIONS ON GEOSCIENCE AND REMOTE SENSING, VOL. 44, NO. 10, OCTOBER 2006 2927. Some quotes: “we apply the voxel discretization of the wet refractivity field already in the GPS processing step. Hence, slant wet delays are described as linear combinations of the refractivities of voxels in GPS processing….. It can be shown that apart from the refractivity of the voxels, the parameters needed to be estimated will be errors in the satellite and the receiver clocks.”

C. Champollion, F. Masson, M.-N. Bouin, A. Walpersdorf, E. Doerflinger, O. Bock, J. Van Baelen, “GPS water vapour tomography: preliminary results from the ESCOMPTE field experiment,” Atmospheric Research 74 (2005) 253–274. This is from France. Used Kalman filtering. Some quotes: “During the ESCOMPTE field experiment, a dense network of 17 dual frequency GPS receivers was operated for 2 weeks within a 2020-km area around Marseille (southern France). The network extends from sea level to the top of the Etoile chain (~700
m high). Optimal results have been obtained with time windows of 30-min intervals and input data evaluation every 15 min. The optimal grid for the ESCOMTE geometrical configuration has a horizontal step size of 0.0580.058 and 500 m vertical step size.”



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