Coastal Ocean Topography and Low-Atmospheric Profiling from GPS Ground-Based Reflections

The uncertainty in the global carbon budget from processes in coastal margins is due in part to inadequate remote topographic measurement of upwelling structures and surface roughness near the coast. A 3-week experiment near Santa Cruz, California, with ground-based and simultaneous airborne GPS receivers, measured the GPS signals directly from the satellites as well as those that reflected off the ocean. This paper focuses on the ground-based measurements. These measurements respond to both the ocean surface topography in the first 20 km off the coast as well as refractivity profiles of the atmosphere. The ground-based observations were taken from 5 degrees elevation to below the horizon. The accuracy of the topographic measurement is potentially at the few-cm level, with resolutions of 0.5 to 5 km. This paper will show the evidence for observing persistent ocean topographic features over a few days. Improper averaging of small-scale surface roughness is an error in determining broad (few-km) topographic features. The unmodeled features of the atmospheric refractivity profile are also an error source for the surface topographic measurement. The level of these topographic errors as well as the potential for measuring atmospheric refractivity features of the lower atmosphere will be explored.