wv3 accuracy study with histogram

The spark that ignited the PhotoSat accuracy studies

wv3 accuracy study with histogram

2016 PhotoSat WorldView-3 satellite surveying accuracy study, Asmara, Eritrea.

“Everything that the last speaker just told you is wrong”.   This shocked me since I was the last speaker.  I was just rejoining the audience after my presentation at a satellite data distributors’ conference in San Diego in 2008.

I had given a presentation on PhotoSat’s experience using satellite photos for elevation mapping.  I had shown comparisons between PhotoSat stereo IKONOS satellite elevation mapping and hundreds of mining exploration drill  collar elevations.  Our results suggested an IKONOS mapping accuracy of better than 1.0m in elevation.

The speaker who followed me showed the published specifications of the IKONOS satellite.  He declared that this proved that the results I had just shown were impossible. Then he went on to talk about his own stereo IKONOS mapping results.  His results showed 5m to 10m in elevation mapping accuracy.

 

Looking for a way to unambiguously measure our accuracy

The speaker who challenged PhotoSat’s results in the San Diego meeting actually did us a huge favor.  Although it did not feel like that as I sat fuming in my chair.  His comments provided the motivation for me to find a way to prove we were right.  After this meeting we set about looking for a way to unambiguously demonstrate the accuracy of the PhotoSat stereo satellite elevation mapping.

 

Searching for a detailed, high quality, ground survey data set

We concluded that to prove our accuracy we needed to find a highly accurate ground survey data set covering hundreds of square kilometers. But where to find it?

About two months later, a light came on.  I realized that we might find the elevation survey data that we needed from a large, regional, mining exploration gravity survey.  The topographic surveys associated with mining exploration gravity surveys are among the most accurate and carefully checked topographic surveys in the world.

 

An old friend tells me about an existing ground survey data set

I phoned Kevin MacNabb, president of MWH Geo-Surveys International.  Kevin did gravity survey contracts for me when I was a geophysicist at BP.  I said “Kevin, I am looking for a large regional gravity survey with thousands of accurate topographic survey points.  I want to use the topographic survey data to measure the accuracy of PhotoSat’s stereo IKONOS satellite mapping.”

I added “it would be great if the data is in an area of sparse vegetation in a remote region of the world.  This way we can prove the accuracy of our stereo satellite topographic mapping and show that we can do this anywhere in the world.”

Kevin replied “how would 45,000 ground survey points covering over a thousand square kilometers just west of Asmara, Eritrea do?”  For us this was the perfect data set. Eritrea was a challenging place to work.  It had just emerged from a civil war.  A perfect place to be mapping from satellites. For a fuller description of the  click this link.

 

Eritrea differential GPS survey crew and equiptment

Asmara Project, Eritrea. MWH Geo-Surveys differential GPS survey crew and equipment. Over 45,000 ground points were surveyed between 2004 and 2008. The Magellan RTK base with a ProMarkTM 500 GPS rover are shown in this photo.

 

The Eritea ground survey data is owned by an existing PhotoSat customer

It turned out that Kevin’s customer for the Eritrea gravity survey, Sunridge Gold, was also a PhotoSat customer for stereo IKONOS mapping.  We negotiated the right to use the 45,000 ground survey points for accuracy studies.  In return, we did some additional stereo IKONOS mapping for the company.

 

PhotoSat’s first comprehensive accuracy study

We were immediately able to use 10,000 of the Eritrea ground survey points to measure the elevation accuracy of 200 km2 of stereo IKONOS elevation grid.  PhotoSat had already produced this elevation grid for Sunridge Gold.  We measured the accuracy of the PhotoSat elevation grid as 48cm Root Mean Square Error (RMSE) and .  The full 2008 IKONOS Eritrea Accuracy study is available to review.

 

PhotoSat accuracy measurement and improvement

Since 2008, PhotoSat has been using the 45,000 Eritrea ground survey points as a test bed to measure accuracy improvements in the PhotoSat processing.  This gives us a quantitative measure of accuracy improvements.  We have shown the results in many conferences and published them.  If there are still disbelievers they are certainly not challenging us publicly.

 

Satellite companies start to provide stereo test data over the Eritrea site.

In 2009, two commercial high resolution satellite companies, GeoEye and DigitaGlobe, provided stereo satellite photos over the PhotoSat Eritrea test area.   The DigitalGlobe data was from the 50cm ground resolution WorldView-1 satellite launched in September 18, 2007.  The GeoEye data was from the 50cm ground resolution GeoEye-1 satellite launched on September 6, 2008.

PhotoSat published elevation mapping accuracy reports for both new satellite systems.  The stereo GeoEye-1 PhotoSat elevation grid had an accuracy of 31cm RMSE, determined by 8,893 ground survey points.  The stereo WorldView-1 PhotoSat elevation grid had an accuracy of 35cm RMSE, determined by over 15,000 ground survey points.

 

WorldView-2 joint DigitalGlobe and PhotoSat news release on Eritrea accuracy study

Soon after the commissioning of the WorldView-2 satellite in early 2010 DigitalGlobe asked PhotoSat to use its new processing system to conduct an accuracy study over the Eritrea test area using stereo WorldView-2 photos.  The PhotoSat Eritrea Accuracy study showed WorldView-2 accuracy of better than 30cm RMSE.  These results were issued as a  on March 16, 2010.  The news release is available here.

 

With accuracy improvement PhotoSat mapping becomes PhotoSat surveying

Once the PhotoSat elevation grids achieved an accuracy of better than 30cm many of our customers began using them in place of ground surveying.  We consequently renamed our products that have accuracy better than 30cm to surveying products.

 

The Eritrea ground survey data set has been used for hundreds of PhotoSat accuracy tests and studies

Since PhotoSat first acquired the 45,000 ground survey points in Eritrea, we have used the data for hundreds of accuracy test and studies.

 

2016 PhotoSat Eritrea accuracy studies

In 2016, we used the current version of the PhotoSat Geophysical Processing System to process a full range a stereo satellite photos over the Eritrea test area.  Some of these results are published on our website on the links below.  The link names include the satellite name, the number of ground control points used in the processing and the RMSE accuracy.

 

WorldView-3, Eritrea, 21 GCP, RMSE 15cm

WorldView-2, Eritrea, 21 GCP, RMSE 14cm

WorldView-3, Eritrea, 2 GCP, RMSE 19cm

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

WorldView-1, Eritrea, 21 GCP, RMSE 19cm

WorldView-1, Eritrea, 9 GCP, RMSE 23cm

Pleiades-1B, Eritrea, 74 GCP, RMSE 26cm

Pleiades-1B, Eritrea, 1 GCP, RMSE 28cm

Kompsat-3A, Eritrea, 11 GCP, RMSE 48cm

Kompsat-3A, Eritrea, 1 GCP, RMSE 53cm

ALOS PRISM, Eritrea, 3 GCP, RMSE 1.4m 

SPOT 7, Eritrea, 1 GCP, RMSE 1.4m

ALOS PRISM, Eritrea, 1 GCP, RMSE 2.4m 

 

If you would like more information on PhotoSat surveying you can visit the following links.

Satellite surveying

Mining Industry Applications

Oil and Gas Industry Applications

Case histories

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 700 stereo satellite surveying projects

PhotoSat has delivered over 700 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