WorldView-2, Eritrea, 2 GCP, 19cm RMSE, July 2016

PhotoSat WorldView-2 stereo satellite surveying accuracy study, Asmara, Eritrea 19cm RMSE

  •  400 km2 surveyed using only two ground reference survey points
  • January 2010 WorldView-2 stereo satellite photos processed by PhotoSat in June 2016
  •  This WorldView-2 satellite elevation surveying accuracy is accurate to 19cm RMSE determined by 4,022 survey checkpoints

Summary report below:

A 1m elevation grid covering an area of 400 square kilometres was produced over a PhotoSat test area in Eritrea. The elevation grid was made by geophysical processing of 50cm ground resolution stereo satellite photos taken by the DigitalGlobe WorldView-2 satellite. The stereo satellite photos and elevation grid referenced two ground survey control points. The elevation surveying accuracy was measured with over 4,000 survey checkpoints.

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

Eritrea satellite photos:

The pair of stereo WorldView-2 satellite photos over the Eritrea test were taken on January 27, 2010 at approximately 10:30 AM local time.

Eritrea elevation grid:

PhotoSat produced a 1m grid of elevations over a 400km2 area. We processed the stereo WorldView photos with our geophysical stereo satellite processing system in June, 2016. An image of the 1m elevation grid is shown below.

Ground reference points:

With this accuracy study we are demonstrating that PhotoSat can produce highly accurate WorldView-2 elevation surveys with only two ground reference points. Having as few as two ground reference points for a 400km2 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 northern point was a photo recognizable point. The southern ground reference point was determined by fitting the satellite elevation grid to a dense set of ground survey points around a topographic high. This fit was within 25cm horizontal and 5cm vertical.

Stereo WorldView-2 elevation image created from the 1m PhotoSat Asmara, Eritrea satellite survey grid. The figure shows the locations of the two ground control points.

Accuracy evaluation check points:

 The accuracy of the PhotoSat 1m survey grid was evaluated with 4,022 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 check points is shown in the check points figure below.

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 consist of a 250m by 250m regional grid of points.

Area of the 25km by 16km Eritrea Stereo WorldView-2 1m elevation grid showing the two ground control points and the 4,022 elevation checkpoints used 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.

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 3,332 elevation checkpoints with slopes less than 20% grade have a Root Mean Square Error (RMSE) of 19cm.

Histogram of the elevation differences between the WorldView-2 stereo satellite elevations for the 25km by 16km area and the 3,332 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 19cm, LE90 31cm.