Low Elevation GPS Slant Observations

Ground based GPS is routinely used to estimate percipitable water vapor (PWV) above a station, and space based GPS has been used for atmospheric refractivity profiling with high vertical resolution. Determination of atmospheric profile information above a ground based GPS station is an ill conditioned problem. We show that very low elevation (0-5 deg.) GPS slant observations, taken on the coast in San Diego, CA contain atmospheric profile information. The analysis technique to obtain these low elevation slant measurements is described, including a new tropospheric mapping technique that was developed for these observations. The low elevation slant observations appear to have several uses: (1) Limited detection of the height of the ocean boundary layer; (2) Determination of electromagnetic signal bending for radar applications; (3) Assimilation into numerical weather models. Experimental work, analysis methods, and applications will be discussed.