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.

How can modern satellites photos possibly be accurate to 20 centimeters in 10 kilometers?

By Gerry Mitchell, P.Geo, President PhotoSat

ground control survey points in eritrea test area

3D WorldView-1 satellite view showing the ground survey points in PhotoSat’s Eritrea test area.

 

My intuition rebels at the notion that a satellite orbiting 750 kilometers above the earth, traveling at 7 kilometers per second, could possibly take photos of the ground accurate to 20 centimeters in 10 kilometers. When you take into consideration that these satellites have scanning cameras which take their photos like push brooms, with the north end of the photo taken a few milliseconds before or after the south end, and that the whole satellite is vibrating while the photos are taken, it boggles the mind. It just does not seem that such high accuracy should be possible. However, the satellite photos themselves, checked with tens of thousands of ground survey points, clearly demonstrate that the accuracy is real.

How do the satellites and cameras work?

We engineers and geoscientists in the commercial realm don’t actually know how these satellites and cameras work. Almost all of the technical details of the imaging satellites, their cameras, and their ground processing stations is classified. Or if it’s not classified it’s certainly very difficult to discover. I’ve had many conversations with satellite engineers who seem like they’d love to tell me why their satellites perform so amazingly well. Sadly, they simply aren’t allowed to discuss classified technology with anyone without the proper security clearances.

Whenever I have one of these conversations, it always seems to me that part of what the engineer knows is public and part is classified, but the engineer cannot be sure that he or she can remember what is still classified and what isn’t so it’s safest to say nothing. I’ve had satellite engineers decline to confirm information that is published on their own company’s website. Needless to say, this can make for some very awkward conversations.

We engineers and geoscientists in the commercial world only have access to the satellite photos themselves, and very general public information about the satellites and their cameras.

How accurate are the satellite photos?

When the Digital Globe WorldView-1 (WV1) satellite photos first became commercially available in 2008, PhotoSat acquired stereo photos for a test area in Eritrea where we have over 45,000 precisely surveyed ground points. When we shifted the WV1 photos 3m horizontally to match any survey point, we were amazed to discover that all of the survey points within 10km matched the satellite photos to within 20cm. We eventually documented this discovery in an accuracy study white paper that is now published on our website.

Now, eight years after that initial WorldView-1 accuracy study of the Eritrea test area, we have processed hundreds of satellite photos from the WorldView, Pleiades, SPOT and KOMPSAT satellites and have come to expect this incredible accuracy. I’m still in awe that this is possible and I still don’t know how it is achieved. I do know that the photos are amazingly accurate.

black and white photo of over 15000 ground survey points in PhotoSat Test Area

WorldView-1 satellite photo over the PhotoSat test area in Eritrea. The over 15,000 ground survey points used to confirm that the satellite photo accuracy is better than 20cm in 10km are shown as black dots. The completely black areas are survey points every 20m along lines separated by 100m.

 

 Colour image of a one meter PhotoSat survey grid produced from the WorldView-1 satellite photos

Colour image of a 1m PhotoSat survey grid produced from the WorldView-1 satellite photos. The ground survey points demonstrate that the PhotoSat grid is accurate to 35cm in elevation.

 

 

Case study: Reducing Suncor’s mature fine tailings inventory

This post is part 2 in a series looking at how Suncor uses our topographic survey data to  assist their Tailings Reduction Operation (TRO). In this post we’ll look at how they use the data to measure the thickness of their mature fine tailings (MFT) dewatering cells.

Background on mature fine tailings

Mature fine tailings are the clays from the bitumen ore that are suspended in the tailings water. To reduce the area and volume of oil sands tailings ponds, tailings water with suspended clay is mixed with a flocculent which causes the clay to settle out. The tailings water is pumped into dewatering cells where clear water drains off for reuse in bitumen processing while the clay is left behind.

PhotoSat has developed a process to measure the thickness of the clay in each of the mature fine tailings cells in thickness intervals of 15cm. We use our highly accurate topographic mapping between two satellite photo dates to create the detailed elevation maps.

Suncor’s MFT designated drying areas:

  • Total surface area 7.5M m2 (1,866 acres)
  • 697 tailings cells
  • 2788 discharge locations
Suncor mature fine tailings areas

Suncor mature fine tailings areas

 

Zoom of MFT designated drying areas

Zoom of MFT designated drying areas

 

How it works

In last week’s post, we saw that Suncor compared our satellite topographic surveys to other survey methods, and has switched to using PhotoSat mapping as their main surveying method for their TRO operation. The success of this service led PhotoSat, in collaboration with Suncor, to develop a process for automatically mapping the thickness of the mature fine tailings dewatering cells in increments of 15cm. This helps them reduce existing mature fine tailings inventory. The isopachs are provided in map (polygons) and tabular forms.

Satellite photo of MFT system 1

Satellite photo of MFT system 1, July 27, 2014                     Elevation image of MFT system 1, July 27, 2014

 

 

Isopachs (thickness) of MFT System 1

Isopachs (thickness) of MFT System 1, June 29 to July 13                  Thickness changes, July 13 to July 27

 

The spreadsheet data we provide also includes MFT volumes since the last pour, the total area in m2 covered by MFTs, the area of the polygons, the utilization of the polygons, and the MFT lift thickness.

Mature fine tailings mapping from our 15cm accuracy topographic surveys improves the monitoring and measurement of the tailings, providing Suncor with a cost-effective and reliable alternative to GPS surveying and aerial LiDAR mapping. Using satellites also reduces safety risks for field crews.

Next time we’ll look at how Suncor has adopted toes and crests mapping as part of their TRO process.

For more info on our topographic surveys contact us at info@photosat.ca.

 

 

Accelerate Mining Volume Measurements with Satellite Topography

Accurate mine planning requires continually adjusting the plans for the situation on – and underneath – the ground. Resource quantities and locations are changing frequently, and mine layout is affected by blasting, tunneling and ore removal. That’s especially true in open pit mines, but all mining engineers face the difficulty of working with the same digital elevation data while the ground shifts.

In fact, that’s one problem that more efficient communication between the mine face and site and the engineer simply can’t solve, because no one on the ground has a high-level overview either. What’s needed is an update of the original elevation data to reflect what’s happened since.

A common method of doing this is with LiDAR (Light Detection and Ranging). But LiDAR is expensive and time consuming, so we need a mapping system that can be used more often. The only snag is that it has to both deliver similar accuracy and cost significantly less to permit more frequent use.

Step forward satellite topography.

Satellite topography using new, geophysical processing techniques results in similar accuracies to LiDAR and can be used for yearly, quarterly or monthly reconciliations, allowing engineers to work with accurate representations of what’s really happening on the ground. PhotoSat’s satellite elevation mapping for mining volumes has proven accuracies of better than 30cm, providing a clearer picture.

Mining volume changes over an open pit

Volume changes over an open pit mine

 

That means that when it’s time to make volumetric change measurements in pits, stockpiles, waste dumps and tailings, satellite mapping lets you view and analyze the situation simply and easily. Our clients tell us that one of the main advantages of using our satellite system is the ease with which they can check on as-built locations of buildings and structures and reconcile them to the original plan. Reconciliation can even be on a biweekly basis if the project is moving fast. That helps engineers with tailings management, and also makes life easier and safer for on-the-ground surveyors, resulting in greater accuracy and fewer injuries.

How can a satellite system deliver biweekly updates? Partly because after ground-based scans have been acquired, the images have to be compiled. In the case of a system like vehicle-mounted ILRIS (Intelligent Laser Ranging and Imaging) that’s the bottleneck; from raw data to point cloud to the computer processing and satellite location necessary to produce a useable image, nothing much can compete with the 8 days PhotoSat’s technology can take to produce a useable result.

Satellite image with mining volumes

Satellite photo with mining volume changes

 

Finally, using satellites rather than ground-based methods removes the need for surveying to take place on or near the mine site. As a result, the surveying process is safe and never needs to interfere with mine operations. There’s no risk of damage to vehicles or injury to surveying personnel when your imaging is done from space!

To find out more about how satellite topographic mapping can help make mining a safer and more efficient process, leave us a comment or contact us at info@photosat.ca.