WorldView-1 Garlock Fault, 1 GCP, 23cm RMSE, October, 2016

  • 174km2 surveyed using only one ground reference survey point
  • This WorldView-1 satellite elevation survey is accurate to 23cm RMSE, determined by comparison to 7,343 elevation check points from a highly accurate LiDAR survey
  • June, 2010 WorldView-1 stereo satellite photos processed by PhotoSat in October, 2016

Summary report below:

Gerry Mitchell, P. Geo, Geophysicist, President PhotoSat
October, 2016

A 1m grid of elevation values, covering an area of 174 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-1 satellite. The stereo satellite elevation processing was referenced to one ground survey point. The elevation surveying accuracy was determined by direct comparison to 7,343 elevation checkpoints extracted from a highly accurate LiDAR survey.

WorldView-1 color image with 50cm contours from the PhotoSat WorldView-1 survey of the California test area.

WorldView-1 color image with 50cm contours from the PhotoSat WorldView-1 survey of the California test area.

The Garlock Fault was surveyed with LiDAR in April, 2008 by OpenTopography. The location of the LiDAR survey and the area of this WorldView-1 stereo satellite survey accuracy study is shown below. We believe this LiDAR survey data to be accurate to better than 5cm RMSE.

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-1 stereo satellite photos, acquired June 20, 2010, is shown by the circle.

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-1 stereo satellite photos, acquired June 20, 2010, is shown by the circle.

An elevation image showing the portion of the Opentopography.org LiDAR survey used in this accuracy study. The dimensions of the area are 14.5km east–west by 12km north–south. Lower elevations are blue and higher elevations are red. The oval is the Honda California Test Track.

An elevation image showing the portion of the Opentopography.org LiDAR survey used in this accuracy study. The dimensions of the area are 14.5km east-west by 12km north-south. Lower elevations are blue and higher elevations are red. The oval is the Honda California Test Track.

WorldView-1 50cm resolution orthophoto, created from the WorldView-1 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-1 50cm resolution orthophoto, created from the WorldView-1 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.

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

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

Stereo WorldView-1 elevation image covering the area of the LiDAR survey. This elevation grid has an elevation point every meter. At this scale, the LiDAR and WorldView-1 images are identical. Low elevations are blue and high elevations are red.

Stereo WorldView-1 elevation image covering the area of the LiDAR survey. This elevation grid has an elevation point every meter. At this scale, the LiDAR and WorldView-1 images are identical. Low elevations are blue and high elevations are red.

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

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 October, 2016.

Ground reference points:

With this accuracy study, we are demonstrating that we can produce highly accurate WorldView-1 surveys with only one ground reference point. Having as little as one ground reference survey point for a 174km2 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 0m E, 1.75m N and 4.34m in elevation to match the LiDAR data. The global accuracy of most WorldView stereo satellite photos is better than 3m.

Accuracy evaluation checkpoints:

The accuracy of the PhotoSat 1m survey grid was evaluated with 7,343 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 7,343 elevation checkpoints with slopes less than 20% grade have an RMSE of 23cm.

Histogram of the elevation differences between the WorldView-1 stereo satellite elevations for the 14.5km by 12km area and the 7,343 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 23cm, LE90 37cm.

Histogram of the elevation differences between the WorldView-1 stereo satellite elevations for the 14.5km by 12km area and the 7,343 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 23cm, LE90 37cm.

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Learn about PhotoSat's WorldView-1 survey accuracy.

Download the Garlock Fault, 1 GCP, 23cm RMSE full report to learn more.

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