GPS Meteorology

My principal research area is the use of the Global Positioning System as an atmospheric remote sensing tool.

When the position of a GPS receiver is precisely known, it is possible to solve for the additional refractive delays in the signals which depend on the density and hence pressure, temperature and water vapor content of the atmosphere.

Since the idea was first proposed in the early 1990's, the advances in the sophistication of GPS data analysis and the enormous increase in the deployment of permanent GPS stations have brought the basic techniques to maturity and attracted the attention of major meteorological agencies.

I have been involved in the development of the use both of ground based as well as space-based GPS receivers for providing measurements, and I see a great potential in atmospheric science for an increasingly valuable exploitation of the data. There is also an untapped source of information in the spectral content of the data that can provide even more detailed information on the water vapor structure of the atmosphere, and these techniques remain to be developed.

Seismology

Earthquake seismology was the focus of my research previous to my involvement in GPS and continues to be of great interest. During my Ph.D. work at Scripps Institution of Technology, I worked with Prof. Guy Masters on developing a tomographic inversion procedure for local earthquake data for simultaneous relocation of the earthquakes and determination of the crustal velocity structure. The method is based on principles of inverse theory for which the faculty at Scripps is well known (Backus, Gilbert, Parker). From this education, I developed a general understanding of inverse problems that has been useful in all my geophysical research since that time.

Following my Ph.D., I devoted 2 years of post-doctoral research to tomography and waveform modeling of southern California earthquakes at the California Institute of Technology, working with Dr. Egill Hauksson, Prof. Hiroo Kanamori, and Prof. Don Helmberger. With the occurrence of the Northridge earthquake (1994) during my stay, I had the exciting opportunity to put my tomographic model to use for wave propagation modeling of amplification of strong ground motion in the Los Angeles basin.

Using earthquakes to study crustal structure is still of interest to me. While I have no current plans for further research in seismology, due to the time constraints of the GPS meteorology research, I remain very interested and open to  collaborations with other seismologists and tectonics faculty on these problems.