Abstract
Abstract. Airborne lidar is a remote sensing method commonly used for mapping surface topography in high resolution. A water surface in hydrostatic equilibrium theoretically represents a gravity potential isosurface. Here we compare lidar-based ellipsoidal water surface height measurements all around the shore of a major lake with a local high-resolution quasi-geoid model. The ellipsoidal heights of the 87 km2 we sampled all around the shore of the 597 km2 lake surface vary by 0.8 m and strong spatial correlation with the quasi-geoid undulation was calculated (R2 = 0.91). After subtraction of the local geoid undulation from the measured ellipsoidal water surface heights, their variation was considerably reduced. Based on a network of water gauge measurements, dynamic water surface heights were also successfully corrected for. This demonstrates that the water surface heights of the lake were truly determined by the local gravity potential. We conclude that both the level of hydrostatic equilibrium of the lake and the accuracy of airborne lidar were sufficient for identifying the spatial variations of gravity potential.
Highlights
The aim of physical geodesy is the determination of level surfaces of the Earth’s gravity field (Hoffmann-Wellenhof and Moritz, 2005)
We conclude that a lake may reach a level of hydrostatic equilibrium that allows it to be used as a basis for mapping a gravity potential isosurface
This can be assessed on the basis of water gauge readings, which can be used to correct the remaining lake-scale dynamic surface topography
Summary
The aim of physical geodesy is the determination of level surfaces of the Earth’s gravity field (Hoffmann-Wellenhof and Moritz, 2005). Variations in the ellipsoidal height of the standing water surface are expected to correlate closely with variations in geoid undulation. Based on this assumption, mean water levels of lakes have been surveyed with GPS floats (Del Cogliano et al, 2007), water-level gauges and satellite altimetry (Cheng et al, 2008; Kingdon et al, 2008) in order to refine local geoid models. A notable exception is the study of Borsa et al (2008a), who survey a dry salt lake by high-resolution GPS topography mapping, and compare the results to local gravity measurements to prove that the salt flat resembles an equipotential
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