3D satellite photo showing some of the 775 ground survey points

PhotoSat publishes 21 new satellite surveying accuracy studies

3D satellite photo showing some of the 775 ground survey points

3D WorldView-2 satellite photo of Asmara, Eritrea, showing some of the 775 ground survey points that determine the 14cm PhotoSat surveying accuracy.

21 PhotoSat surveying accuracy studies from seven different stereo satellites

PhotoSat has published 21 new satellite surveying and mapping accuracy studies, now available on our website. The studies include data from seven different stereo satellite systems. The best results show elevation surveying accuracies of better than 15cm.

The accuracy studies include stereo satellite data from the following satellites:

  • WorldView-1
  • WorldView-2
  • WorldView-3
  • Pleiades-1B
  • KOMPSAT-3A
  • SPOT-7
  • ALOS PRISM

 

PhotoSat has measured accuracy on over 750 stereo satellite surveying projects

PhotoSat has delivered over 750 satellite surveying projects since 2007 and we have carried out accuracy evaluations on the majority of them. Most of the survey data on these projects belongs to our customers and cannot be shared publically; however, customers have provided feedback on many of these projects.

The results of these 21 new accuracy studies are consistent with our project accuracy evaluations and customer feedback.

 

PhotoSat accuracy test areas in Eritrea and California

The accuracy studies were conducted over two test areas. One test area is west of Asmara, Eritrea where PhotoSat has access to more than 45,000 ground survey points over a 50km by 20km block.

The second area is in SE California where PhotoSat uses a very accurate Opentopography.org open source LiDAR survey.

 

The effect of different numbers of ground survey points

The studies employed different numbers of ground survey control points for each test area and each satellite system. For some of the satellite stereo pairs the accuracy is significantly improved by increasing the number of ground survey control points.

For example, the WorldView-2 survey for Eritrea is accurate to 19cm in elevation with two ground control survey points, and accurate to 14cm in elevation with 21 ground control points.

In contrast, the accuracy of the WorldView-3 survey for the California test area is not improved by additional ground survey points. This WorldView-3 survey is accurate to 13cm in elevation with one ground survey control point and with 153 ground survey control points.

 

PhotoSat has been continuously producing satellite accuracy studies since 2007

In order to provide objective quantifiable accuracy data for stereo satellite surveying and mapping, PhotoSat has been continuously producing accuracy studies since 2007. We have previously published nine of these studies. The rest of the studies were used for calibrating and improving our processes.

 

21 new accuracy studies all processed with the same version of the PhotoSat processing system

The 21 new accuracy studies were produced with the most recent version (2016) of the PhotoSat processing system. Where possible we used satellite data produced by the 2015 or 2016 versions of the satellite operators’ ground processing systems.

 

Summary of PhotoSat 2016 accuracy study results

Satellite Test area km² GCP RMSE
WorldView-3 California 150 1 13cm
WorldView-3 California 146 153 13cm
WorldView-3 Eritrea 100 21 15cm
WorldView-2 California 173 1 15cm
WorldView-2 California 173 153 12cm
WorldView-2 Eritrea 100 21 14cm
WorldView-1 California 174 153 14cm
WorldView-3 Eritrea 198 2 19cm
WorldView-2 Eritrea 400 2 19cm
WorldView-1 Eritrea 100 21 19cm
WorldView-1 California 174 1 23cm
WorldView-1 Eritrea 420 9 23cm
Kompsat-3A California 144 14 21cm
Pleiades-1B Eritrea 189 74 26cm
Pleiades-1B Eritrea 189 1 28cm
Kompsat-3A California 144 1 50cm
Kompsat-3A Eritrea 130 11 48cm
Kompsat-3A Eritrea 130 1 53cm
SPOT 7 Eritrea 1,458 1 4m
ALOS PRISM Eritrea 2,300 3 2m
ALOS PRISM Eritrea 2,300 1 4m

See PhotoSat’s accuracy studies overview for full details.

For more information about PhotSat’s surveying accuracy, please see our satellite surveying case histories or visit the following links.

Satellite surveying

LiDAR and satellite elevation data

PhotoSat verifies accuracy of DigitalGlobe’s 30cm WorldView-3 satellite elevation data to within 15cm

PhotoSat has recently completed a study to measure the accuracy of the elevation grid produced from the new 30cm resolution WorldView-3 (WV3) satellite. We measured the accuracy of our topographic mapping by comparing it to a highly accurate LiDAR elevation grid. The study was carried out over an 88 km2 area in Southeast California that overlaps an Open Topography LiDAR survey.

Read the full elevation accuracy report here (PDF)

For the study, PhotoSat produced a 50cm grid of elevations using our proprietary geophysical processing technology with stereo satellite images taken by WV3. Our resulting elevations were then compared to a 50cm LiDAR elevation grid, which is accurate to about 5cm. The resulting 15cm RMSE elevation accuracy was impressively achieved using a single ground reference point.

Below are some images of the elevation surveys and the differences between the datasets. You can also view the full WorldView-3 elevation accuracy study (PDF) on our website.

For more information on our highly accurate satellite topography, contact us at info@photosat.ca or 1-604-681-9770.

WV3 30cm resolution satellite ortho photo
Figure 1: WV3 30cm resolution satellite ortho photo created from WV3 stereo photos, for the area of the LiDAR survey used in this study.

LiDAR elevation grid
Figure 2: An image showing a portion of the LiDAR elevation grid. Lower elevations are blue, and higher elevations are red.

PhotoSat’s WV3 elevation grid image
Figure 3: PhotoSat’s WV3 elevation grid image covering the area of the LiDAR image. The grid has an elevation point every 50cm. At this scale, the LiDAR and WV3 images are identical. Lower elevations are blue, and higher elevations are red.

PhotoSat’s WV3 elevation grid clipped to the LiDAR extents
Figure 4: PhotoSat’s WV3 elevation grid clipped to the LiDAR extents, for areas with slopes less than 20% grade. Areas where development occurred since the 2008 LiDAR survey were removed for the accuracy analysis.

Differences between our WV3 elevation grid and the LiDAR elevation grid
Figure 5: The differences between our WV3 elevation grid and the LiDAR elevation grid, for areas with slopes less than 20% grade, are shown in a standard histogram on the left and a cumulative histogram on the right. If we assume that the LiDAR is perfect, the WV3 elevations have a Root Mean Square Error (RMSE) of 15cm. Ninety percent of the WV3 elevations are within 22cm of the LiDAR elevations giving a 90% Linear Error (LE90) of 22cm.

Comparison of the LiDAR and WV3 elevation grids for 1000m wide area
Figure 6: Comparison of the LiDAR and WV3 elevation grids for 1000m wide area. Minor differences between the elevation grids are visible at this scale.

Continue reading PhotoSat verifies accuracy of DigitalGlobe’s 30cm WorldView-3 satellite elevation data to within 15cm