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Geodetic GPS ground surveys that have centimeter-scale horizontal and vertical accuracy serve to calibrate and evaluate the accuracy of airborne surveys and to bring various topographic data, such as beach profiles measured with electronic total stations, into a common reference frame. Kinematic vehicle surveys also provide high-accuracy topographic data of beaches.

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Figure 1. Static geodetic GPS surveys, real-time differential GPS surveying and navigation, and surveying by means of electronic total stations.

Figure 2. Kinematic GPS surveys of beached for coastal research.

Figure 3. This figure shows the distribution of elevation measurements along a 100 meter length of beach at Galveston Island State Park. The blue circles (o) are data points from a kinematic GPS vehicle survey conducted on 1 May 1995. The position and elevation of a GPS antenna mounted on a 4x4 vehicle was measured twice per second as the vehicle made seven passes along the beach. The red crosses (+) are laser ground points collected during two aircraft passes on 6 August 1998. The airborne laser operated at 5000 pulses per second and scanned a swath approximately 350 m wide. A two-meter grid is superimposed on this map view to illustrate the data density possible with airborne laser terrain mapping (ALTM).


Figure 4. Three-dimensional surfaces of the beach constructed from the vehicle and ALTM elevation data. The horizontal blue lines represent 10-cm contour intervals and the bold, red line is the -27.2 m height above the WGS84 reference ellipsoid. The vertical exaggeration is 2.4x. The kinematic GPS vehicle survey has an RMS of about 1 cm and the resulting surface is precise enough to reveal subtle features such as beach cusps. These ALTM data have an estimated RMS of 9 cm and the beach surface derived from laser mapping is subsequently rougher. Nevertheless it is still easy to distinguish the major features of the coast such as the foredune, berm, and beachface. The obvious advantage of ALTM is the data continuity across the beach and back barrier area. The advantage of the kinematic vehicle survey is the superior accuracy capable of measuring subtle rhythmic features along tens of kilometers of beach.


For more information, please contact Jeff Paine

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