PhotoSat WorldView-1 stereo satellite surveying accuracy study, Asmara, Eritrea, 9 GCP, RMSE 23cm

  • 420 km2 surveyed using only nine ground reference survey points
  • This WorldView-1 satellite elevation surveying accuracy is accurate to 23cm RMSE, determined by 2,721 survey checkpoints
  • October 2008 WorldView-1 stereo satellite photos processed by PhotoSat in November 2016

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

A 1m grid of elevation values covering an area of 420 square kilometres was produced over a PhotoSat test area in Eritrea. 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 referenced nine ground survey points. The elevation surveying accuracy was measured with over 2,500 survey checkpoints.

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

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

Eritrea satellite photos:

The pair of stereo WorldView-1 satellite photos over the Eritrea test area were taken on October 23, 2008 at approximately 11:00 AM local time.

Eritrea elevation grid:

PhotoSat produced a 1m grid of elevations over a 420km2. We processed the stereo WorldView photos with our geophysical stereo satellite processing system in November, 2016. An image of the 1m elevation grid is shown below.

Ground reference points:

With this accuracy study we are demonstrating that we can produce highly accurate WorldView-1 surveys with a reasonable distribution of ground reference survey points. Having as little as nine ground reference points for a 420 km2 satellite surveying project is not uncommon in mining exploration projects.

The locations of the ground reference points are shown on the elevation image below. The survey crew and system are shown in the figure below.

Stereo WorldView-1 elevation image created from the 1m PhotoSat Asmara, Eritrea satellite survey grid. The figure shows the locations of the nine ground control points.

Stereo WorldView-1 elevation image created from the 1m PhotoSat
Asmara, Eritrea satellite survey grid. The figure shows the locations of the nine ground control points.

Accuracy evaluation checkpoints:

The accuracy of the PhotoSat 1m survey grid was evaluated with 2,271 ground survey check points. These points were originally surveyed for a large mining exploration gravity survey conducted between 2004 and 2008 by MWH Geophysics. The distribution of the elevation checkpoints is shown in the check points figure.

The elevation check points were surveyed to an accuracy of 2cm using Real Time Kinematic GPS survey equipment. One of the MWH Geophysics survey teams and their equipment are shown below. The accuracy check points were extracted from a 250m by 250m regional grid of survey points.

Area of the 23.7km by 17.7km Eritrea Stereo WorldView-1 1m elevation grid showing the nine ground control points and the 2,721 gravity survey stations used as elevation checkpoints to determine the accuracy of the stereo satellite survey.

Area of the 23.7km by 17.7km Eritrea Stereo WorldView-1 1m elevation grid showing the nine ground control points and the 2,721 gravity survey stations used as elevation checkpoints to determine the accuracy of the stereo satellite survey.

 

MWH Geo-Surveys differential GPS survey crew and equipment. The Magellan RTK base with a ProMarkTM 500 GPS rover are shown in this photo.

MWH Geo-Surveys differential GPS survey crew and equipment. The Magellan RTK base with a ProMarkTM 500 GPS rover are shown in this photo.

 

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 2,721 elevation checkpoints with slopes less than 20% grade have a Root Mean Square Error (RMSE) of 23cm.

Histogram of the elevation differences between the WorldView-1 stereo satellite elevations for the 23.7km by 17.7km area and the 2,721 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 38cm.

Histogram of the elevation differences between the WorldView-1 stereo satellite elevations for the 23.7km by 17.7km area and the 2,721 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 38cm.

 

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