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

geologic formations in northern iraq

The accidental discovery of a new way to produce accurate elevation surveys from satellite photos

By Gerry Mitchell, P.Geo, President, PhotoSat

geologic formations in northern iraq

3D WorldView-2 image looking along dipping geologic formations in Northern Iraq. Produced by PhotoSat.

 

In an effort to find a faster way to produce elevation surveys from satellite photos, PhotoSat geophysicist Michael Ehling and I accidentally discovered a novel way to greatly improve the accuracy and resolution of satellite topographic survey results.

It was 2007, during the peak of the natural resource boom and PhotoSat could not keep up with the demand from Vancouver mining companies who needed accurate satellite survey data for their projects in remote parts of the globe. Without accurate ground surface surveys the mining engineers couldn’t produce reports of ore body volumes. Without the engineering reports the companies couldn’t report their mining discoveries to a booming stock market waiting expectantly for their news.

Interactive photogrammetric processes

Michael and I had been watching how photogrammeters produced elevation surveys from stereo satellite photos since 2004, when stereo IKONOS satellite photos first became available. PhotoSat was buying stereo IKONOS satellite photos from Space Imaging, now part of DigitalGlobe.

We were reformatting the photos so that the photogrammeters could produce elevation surveys using computer systems that had been designed for processing stereo photos taken from airplanes. They were using highly interactive processes and were taking an average of 150 hours to produce satellite surveys for 100 square kilometer projects.

Automatic matching

Michael and I could see that the processors spent most of their time interactively measuring the matches between identical features on pairs of satellite photos. The photos had been taken with the satellite looking at the same area on the ground from different directions. By identifying identical ground features on each of the photos, and precisely measuring their locations, the elevations of the features can be computed.

When Michael and I asked if the photo feature matching could be done automatically we were told that the automatic process usually didn’t work, but when it did, editing the results took more time than doing the matching interactively, so no one used it. As geophysicists we were intrigued by what looked like an interesting technical challenge.

Oil and gas seismic processing tool box

In the 1980’s and 90’s when I was working as a Geophysicist in oil and gas exploration I processed a lot of seismic data. Oil and gas seismic survey data is used to image geological formations thousands of meters below ground in the search for oil and gas. Seismic data processing has always been one of the most complex and computer intensive data processing fields, with expenditures of billions of dollars annually.

Over the past 50 years seismic processors have developed an immense array of data processing tools, including many automatic image matching tools, and I thought that we could probably apply these to the satellite photos.

Gerry and Michael at the siesmic workstation

Oil and Gas seismic processing and interpretation workstation. Gerry Mitchell on the left and Michael Ehling on the right. This technology was the inspiration for the PhotoSat satellite processing system.

Michael tested seismic processing image matching tools on stereo IKONOS satellite photos for several months in 2007. He had to format the digital satellite photos so that they would look like seismic data to the seismic processing systems, run tests, and then reformat the results to look like photos again.

We were in search of a faster way to produce the survey results that the photogrammeters were spending hundreds of hours to produce. We were testing with a pair of IKONOS satellite photos that had already been processed by the photogrammeters so that we could compare our results with theirs.

Gerry, Michael and Jayda at workstation

Michael, Jayda and Gerry using the PhotoSat Workstation on a satellite surveying project.

 

Initial PhotoSat processing test results were amazing

After three months of testing we had our first real success. We were astounded by the results. We could see many fine topographic details on our test data that were simply not visible at all in the photogrammetric processing.

We continued to refine the process over the next few months until we had produced satellite survey results that were over three times as accurate as the photogrammetric processing and had much more topographic detail. The initial process took over 100 hours of computer processing time to process 100 square kilometers, so we had not really found a faster way to produce the results, but completely unexpectedly, we had found a way to produce better results.

comparision of photosat survey

Satellite survey of a river valley processed by conventional photogrammetric methods on the left and by PhotoSat processing on the right. The PhotoSat surveying shows fine topographic detail on the river flood plain that has no expression on the conventional processing.

New PhotoSat Workstation built from scratch

Now, nine years after our initial accidental discovery we still have a team of researchers and software engineers improving our satellite processing system.

Several years ago they replaced the seismic processing system with a computer system built from scratch to efficiently apply the seismic algorithms and processes to satellite photos. This system, the PhotoSat Workstation, was designed to harness the processing power and speed of Graphics Processing Units (GPUs). The GPUs process numerical data a thousand times faster than CPUs. Older software that is retrofitted to use GPUs typically shows speed improvements of two to five times.

It took several years and several million dollars of software development, but since our initial discovery in 2007 we have successfully created an automatic process that produces satellite surveys much faster than the photogrammeters, with much higher accuracy and better topographic detail.

 

 

 

 

 

PhotoSat 1m elevation image of a tailings beach, with 15cm vertical accuracy

The Challenge of Mine Tailings Beaches and Elevation Mapping

Mine tailings beaches are notoriously difficult to monitor. They’re the hardest surveying task at a mine. Data needs to be up to date, but tailings ponds can be huge: Suncor’s tailings ponds cover over 30 square kilometers. Ground survey teams can’t get close enough for safety reasons, and aerial LiDAR data delivery can be frustratingly slow. Low-flying drones are challenged by cold weather, and cannot cover much distance in a day, so are not reliable when measurements are required for a larger area on the same day.

That’s the challenge Suncor faced at its Alberta oil sands mine. Surveying Suncor’s Tailings Reduction Operation (TRO) site meant getting accurate data quickly over a mine site covering over 270 square kilometers. And when Suncor tried using traditional GPS, they found that only about 20% of the site was safe for crews to access. The next step was to try 3D laser scanners, but these simply couldn’t produce enough data fast enough; multiple set-ups were required and yielded sparse data that required significant processing to be comprehensible and usable. This meant adding to an already too-long wait time, as well as additional expense.

Elevation mapping solutions

PhotoSat’s 15cm accuracy satellite topography (DEM) addresses the challenge. Because we use high accuracy satellites, the data is collected safely and easily, reducing the need for ground crews to expose themselves to hazards. And we can collect satellite photos anywhere in the world, making them ideal for remote or challenging terrain.

50cm satellite ortho photo

50cm resolution satellite ortho photo of a tailings beach. © DigitalGlobe 2013

 

PhotoSat elevation image of a tailings beach

PhotoSat 1m elevation image of a tailings beach, with 15cm vertical accuracy

 

Once the satellite imagery has been acquired, we run it through our unique processing system, developed for the industry by us from seismic data processing tools, with engineers in mind.

We have proven the accuracy of our elevation mapping using tens of thousands of ground control points as comparison. Numerous proof of accuracy studies are available on our website.

We map the entire Suncor site every two weeks, providing usable elevation surveys only five days after data acquisition for use in Suncor’s bi-weekly engineering meetings. Our satellite mapping provides an instantaneous snapshot of the entire tailings beach waterline, the geometry of the beaches, and the height of the tailings dykes. We continue to map the Suncor Millennium and Steepbank mines every two weeks, including mapping the Mature Fine Tailings cells in thickness increments of 15cm.

The digital elevation models are also used for mapping windrows, monitoring tailings dykes, calculating volume changes, and verifying the locations of as-built infrastructure. When Suncor’s tailings engineers need to make a decision, they have the reliable, up-to-date data to base it on.

The original presentation made my Suncor at the 2014 Trimble conference that compares PhotoSat mapping to alternatives, can be viewed here.

To learn more or get a quote for topographic mapping for your resource project, contact us at info@photosat.ca or 1-604-681-9770.

Seismic survey points

Improve Seismic Survey Planning with Highly Accurate Elevation Models

When planning a seismic survey, petroleum engineers need to know which seismic source points can be accessed safely by vibroseis trucks. Using high detail elevation models generated from satellite imagery, PhotoSat can help.

We use elevation surveying to prepare the groundwork for seismic surveying. Before holes are drilled or vibroseis trucks are on the move, planners know where the likely best spots are. And thanks to PhotoSat’s 30cm accuracy elevation models, they also know where trucks can’t go.

Overturning vibroseis trucks on steep or sudden inclines is a real risk. Planners need more than contour lines: they need high resolution, accurate topographical data to allow them to plan how to best use their vibroseis equipment while keeping their trucks and crews safe. Mapping the ground slope to within 30cm elevation accuracy enables mapping of no-go zones that are too steep for vibrator truck operations, lowering the risk of overturning the vibes on steep inclines. Our clients tell us that this improvement in seismic survey planning helps them reduce project costs and saves time.

Seismic survey points

 

Advance scouting is expensive, risky and time-consuming. And it comes under fire for its environmental impact. PhotoSat’s proprietary geophysical processing system allows us to create usable digital elevation models and precision satellite images within just a few days of a satellite acquisition, with 30cm elevation accuracy and with no boots – or tires – on the ground. The resultant data can then be used for subsequent project engineering and design.

Another advantage of having accurate survey data in the early project stages is the ability to use the elevation models for quality control of the seismic shot and receiver point survey data. In addition, the data is engineering-quality and can be used for all future design and construction work. This reduces survey wait times and allows managers to have increased faith in the reliability of the data.

So how do we get these kinds of accuracies? We have developed our own unique process, and more information can be found on the Technology page. Also, we have published numerous Proof of Accuracy Reports, that compare our elevation data to tens of thousands of independent survey points.

If you’d like to learn more about how PhotoSat built software developed for seismic data processing into a powerful, fast and accurate satellite surveying tool, or find out how that tool can help your project happen, contact us at info@photosat.ca or 1-604-681-9770.