Stereo Satellite Elevation Surveying: Ghadames, Libya
From August to November of 2010 PhotoSat produced a 3,962 km² 1m survey grid from 50cm WorldView-2 stereo satellite photos for a project in Ghadames, Libya. The client hoped that by utilizing stereo satellite elevations during and after a highly accurate seismic survey they could improve the efficiency of their project.
The stereo satellite elevation surveying was initially referenced to 19 ground survey targets and 85,000 seismic source points with precise GPS elevations, as shown in Figure 1. The resulting horizontal match between the targets and the 50cm resolution stereo WorldView-2 satellite photos was approximately 25cm.
Following the completion of the DEM processing an additional 86,000 seismic source points were provided in the southern portion of the survey area, further confirming the close match between the source point elevations and the stereo satellite elevations.
Figure 2 shows the standard deviation and mean differences between the seismic shot point elevations and the stereo satellite elevations. The northern edge, which contains 53,000 seismic shot points, has a standard deviation of 30cm and mean difference of 5cm in elevation. The southern portion, which contains 118,000 seismic shot points, has a standard deviation of 28cm and mean difference of 8cm in elevation.
The availability of the satellite imagery and DEM has: reduced advanced scouting by ~80%; enabled safer vibroseis operations due to the identification of steeply sloped areas as no-go zones; resulted in fewer surveyor field days; and, provided a reliable comparison data set for quality control purposes. By using stereo satellite elevations to complement an ongoing seismic survey the client could improve the efficiency of their resource management and gained increased confidence in both data sets.