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

Satellite survey of Libya with ground survey points

Are PhotoSat satellite surveys really more reliable than ground surveys?

By Gerry Mitchell, P.Geo, President PhotoSat

Satellite survey of Libya with ground survey points

World View 2 satellite survey in Libya with ground survey points for 3D oil and gas seismic survey.

 

In 2008, I would get a hollow feeling in the pit of my stomach whenever customers phoned or emailed to tell us that the PhotoSat surveys did not match their ground surveys. Back then, I was sure there was a problem with the satellite photos, or that we had made some terrible mistake in our processing.

However, by 2013 our customers were using PhotoSat satellite surveys to check and adjust their ground surveys.

Ground surveys right, PhotoSat surveys wrong?

Back in 2008 it was clear to everyone, including me, that ground survey data was right and satellite survey data wrong. After all, ground survey data was collected by someone who had stood on the ground. It was the “ground truth”.

In comparison, the PhotoSat surveys were produced from satellite photos taken from 750 kilometers above the earth. Of course the ground surveys were right and the satellite photo surveys were wrong. Or so we thought. As we did more and more satellite surveying projects, we began finding obvious ground survey errors. Some of these projects had thousands of ground survey points.

ground target at mining project drill hole

Ground target at a mining project drill hole with arms 20cm wide and 1m long. The image to the right show how this target appears on a 50cm ground resolution GeoEye satellite photo.

 

Some ground surveys wrong, PhotoSat right

We began finding projects with two sets of ground survey data, one set matching the PhotoSat surveying perfectly and the other set mismatching. Investigating these cases with customers was eye-opening and often entertaining.

On one project in southern Mexico, all of the ground survey points on or near roads matched the PhotoSat surveying perfectly. The points in remote areas, particularly on the tops of hills, had differences of two to five meters in elevation.

So what happened? The contract surveyor had used his high quality, bulky, GPS surveying equipment for the survey points that he could drive to. But he had sent his young assistant with a hiker’s GPS to all of the survey points on the hilltops. The surveyor was confident that the client would never check those remote points.

By 2010, we had become much more confident in the accuracy and reliability of our PhotoSat surveying. When there was a mismatch between PhotoSat surveying and ground GPS surveying we began suggesting that the PhotoSat surveying was “usually right”.  As you can well imagine, many of our customers, and all of their surveyors, were sure that I was delusional.

We had to find another strategy. We began saying, “Thanks for telling us about our mistake. Please send us a copy of your survey data and we will see if we can identify and fix our problem”.

Drill hole with 40cm by 40cm white concrete block

Drill hole with a 40cm by 40cm white concrete block on a mining project in central Mexico. The drill holes on this project were surveyed three times by three different GPS survey contractors. The coordinates of this drill hole on the three surveys are shown on an extreme zoom of the PhotoSat WorldView satellite survey. The PhotoSat survey has more reliable coordinates than any of the 3 GPS surveys.

 

Not all GPS surveys created equal

We also learned that not all ground GPS surveys are created equal. All good quality GPS systems record the GPS signals for later processing, so we began asking for copies of these GPS recordings along with the GPS ground survey coordinates.

The effect of this simple request on the quality of the survey data was remarkable. Some surveyors would immediately go and resurvey the ground points as soon as we asked for the GPS recordings.

By processing the GPS recordings we could see how long the surveyors had been at each point. In many of the significant mismatches, we discovered that the GPS recording times were much too short for ten centimeter accuracy. At first we had pushback from many surveyors when we suggested that their coordinates were probably inaccurate.

Then in June, 2011, the International Association of Oil and Gas producers published a thick report of guidelines for GPS surveying, freely available as a PDF file. For us this was a godsend.

Whenever there was debate about GPS accuracy, we would email a copy of the report saying, “These are the guidelines that we are relying on.  Please tell us where they are wrong”. All the discussions about recording times for GPS accuracy stopped.

Most ground surveys are good quality

Of course, it’s worth noting that most of the ground surveys that we receive are very good. Only occasionally are there serious problems that we cannot easily resolve. And of course PhotoSat also makes occasional processing errors and mistakes.

We always investigate whenever the PhotoSat surveying does not match the ground surveying. When we find it to be our mistake, we fix the PhotoSat survey data and resend it to the customer at no cost.

Correcting multiple mismatching ground surveys

By 2013, many of our repeat customers no longer assumed that the PhotoSat surveys were wrong when they did not match their ground surveys. In just five years there had been a 180 degree shift. In 2008, ground surveying always proved that PhotoSat surveying was wrong. By 2013 the PhotoSat surveying was being used to quality check and fix ground surveying.

This is great for projects with several different ground surveys. These are often surveyed by different contractors. For example, we have one case of an oil and gas project with five different ground GPS surveys performed by five different contractors. We proved that none of the ground surveys matched any of the other four ground surveys.

The key ground survey was for an oil well that discovered several hundred million barrels of oil. We matched the PhotoSat survey to the discovery well. All of the other four surveys mismatched the PhotoSat survey, each by different horizontal and vertical distances.

We used the PhotoSat survey to measure the offsets of each of the ground surveys from the oil well. Then we adjusted the other four surveys to match the oil well. This gave the project a consistent set of ground surveys all matched to the oil well.

This case history is described in more detail here.

Give GPS surveys on an oil and gas poject

Five GPS surveys on an oil and gas project. Each was done by a different survey contractor. None of the surveys matched each other. PhotoSat detected the mismatches and adjusted the survey data to produce a coherent survey data set.

 

Please see the experience section of the PhotoSat website for additional case histories and accuracy studies.

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.

 

 

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.

Reconciling Surface Engineering Data

One of the biggest complaints we hear from our oil and gas clients is about inconsistent survey data. On the one hand, they’re spending thousands of dollars on surface engineering data, and the cost is justified because of its business value. That data saves money down the line. Except it doesn’t. Because when drilling, completions and facilities engineers get the data, they often can’t trust it.

It’s data that comes from GPS and theodolite surveys, as-built drawings, and from other sources that aren’t always even identified. Any given data point could have come from any of these sources. Frequently the engineering data is not reliable enough.

What’s needed is a data set that comes from one, reliable source. Then existing data sets can be compared against that. Instead of several differing views, there’s one authoritative, reconciled picture of what’s happening on the ground.

PhotoSat offers our oil and gas clients coherent project location data with elevation accuracies better than 20cm. Completions, facilities and drilling engineers can work from a reliable data set now and in future project stages.

Survey data sets for engineering projects

The value of surface engineering data is directly proportional to accuracy. We help our clients maximize the value of their engineering data by providing reliable data across the project site. That data can be used to inform cut and fill volume estimates as well as to streamline facilities engineering projects and well pad selection.

Additionally, surveying via satellite means less boots on the ground. Fewer survey teams have to work in hazardous working environments and less expensive equipment is exposed to the risk of damage at the project site. Data is also available in a usable form far more quickly, typically within five days.

So how does it work?

We start with the data set our client already has. Then we compare it against our own topographic survey. When we find inconsistencies, we work with the client’s project team to select the appropriate reference data set for that inconsistency, and shift the others horizontally and vertically to match it. This process usually means we’re leaving our clients with datasets that match to within 10cm vertically and 25cm horizontally. Clients also get a matching 1m grid of our satellite engineering topography, accurate to 20cm in elevation, and a 50cm precision satellite ortho photo with 25cm horizontal accuracy. That provides a reliable basis for future data-dependent engineering projects like surface design work, including cut and fill volume estimates.

We’ve delivered over 500 projects like this to clients all over the globe, and our clients know that there’s no better, faster or more accurate way to base their engineering data on something reliable and accurate. If you’d like to read more about how our data reconciliation process works, take a look at this engineering data case study. To find out how we can help you with your project, contact us at  info@photosat.ca or call us at 1-604-681-9770.