WorldView-2, Garlock Fault, 1 GCP, 15cm RMSE, August 2016

PhotoSat WorldView-2 stereo satellite surveying accuracy study, Garlock Fault, California, 15cm RMSE

  • 173 km2 surveyed using only one ground reference survey point
  • This WorldView-2 satellite elevation survey is accurate to 15 cm RMSE, determined by comparison to 7414 elevation check points from a highly accurate LiDAR survey
  • April 2010 WorldView-2 stereo satellite photos processed by PhotoSat in August 2016

Gerry Mitchell, P. Geo, Geophysicist, President PhotoSat

 August 2016

Summary report below:

A 1m grid of elevation values, covering an area of 173 square kilometres, was produced over a PhotoSat test area in California. The elevation grid was made using geophysical processing of 50cm ground resolution stereo satellite photos taken by the DigitalGlobe WorldView-2 satellite. The stereo satellite elevation processing was referenced to one ground survey point. The elevation surveying accuracy was determined by direct comparison to 7414 elevation check points extracted from a highly accurate LiDAR survey.   

WorldView-3 orthophoto with contours Garlock Fault California

WorldView-2 color image with 50cm contours from the PhotoSat WorldView-2 survey of the California test area.

The Garlock Fault was surveyed with a LiDAR in April 2008 by OpenTopography. www.opentopography.org.The location of the LiDAR survey and the area of this WorldView-2 stereo satellite survey accuracy study is shown below. 

Opentopography LiDAR data Garlock Fault California

The Garlock Fault Opentopography LiDAR survey shown on Google Earth. The Garlock Fault LiDAR survey was flown in April 2008. The location of the WorldView-2 stereo satellite      photos, acquired April 29, 2010, is shown by the circle.

LiDAR elevation grid, Garlock Fault California

An elevation image showing the portion of the Opentopography.org LiDAR survey used in this accuracy study. The dimensions of the area are 14.4 km east–west by 12 km north–south. Lower elevations are blue and higher elevations are red. The oval is the Honda California Test Track. 

WorldView-3 satellite orthophoto Garlock Fault California

WorldView-2 50cm resolution orthophoto, created from the WorldView-2 stereo photos, for the area of the LiDAR survey used in this study. The 7.5 mile oval track is the Honda California Test Track. The single ground reference point is shown as a white cross.

WorldView-2 satellite photo Honda Test Track California

Ground reference point used for the Honda California Test Track area.

WorldView-3 satellite survey elevation grid California

Stereo WorldView-2 elevation image covering the area of the LiDAR image in Figure 3. This elevation grid has an elevation point every meter. At this scale, the LiDAR and WorldView-2 images are identical. Low elevations are blue and high elevations are red.

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Elevation checkpoints for areas with slopes of less than 20% grade.

California elevation grid:

PhotoSat produced a 1m grid of elevations over the entire project area. We processed the stereo WorldView photos with our geophysical stereo satellite processing system in August 2016.

Ground reference points:

With this accuracy study we are demonstrating that we can produce highly accurate WorldView-2 surveys with only one ground reference point. Having as few as one ground reference survey point for a 178 km2 satellite surveying project is not uncommon in mining exploration projects.

Global shift of stereo satellite survey to match ground reference:

The WorldView ortho photo and elevation grid needed a constant shift of only -0.9m E, 0.8m N and 0.69m in elevation to match the LiDAR data.  The global accuracy of most WorldView stereo satellite photos is better than 3 m.

Accuracy evaluation check points:

The accuracy of the PhotoSat 1m survey grid was evaluated with 7414 elevation checkpoints derived from the LiDAR elevation grid.

Elevation survey accuracy statistics:

The Guidelines for Digital Elevation Data of the US National Digital Elevation Program (NDEP) recommends that elevation checkpoints should be chosen in areas with slopes less than 20% grade. The 7414 elevation checkpoints with slopes less than 20% grade have an RMSE of 14.8 cm.

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Histogram of the elevation differences between the WorldView-2 stereo satellite elevations for the 14.4 km by 12 km area and the 7414 elevation checkpoints with slopes less than 20% grade. The Guidelines for Digital Elevation Data of the US National Digital Elevation Program (NDEP) recommends that elevation checkpoints should be chosen in areas with slopes less than 20% grade. RMSE 15 cm, LE90 24 cm.

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