Ground control point

What mapping and surveying accuracy do I need for my mining exploration project?

By Gerry Mitchell, P.Geo, President PhotoSat

GPS survey of a PhotoSat survey ground control point.

Accurate topographic mapping and surveying of a mining exploration project requires a significant investment of time and resources.

 

For early stage mining exploration project work, 3m survey accuracy is sufficient.

Early stage mining exploration project work:

  • Geological mapping and outcrop sampling
  • Geochemical surveys
  • Geophysical surveys: magnetics, electromagnetics, induced polarization, gravity

Most early stage mining exploration projects require mapping quality topography, accurate to about 3m horizontally and 3m in elevation. This is similar to the accuracy of the hand held GPS units used by most exploration geologists to record geological observations and sample locations.

 

For exploration drilling up to the “discovery” drill hole, 3m survey accuracy is sufficient.

The initial exploration drilling will be focused on geological, geochemical or geophysical targets. Location of drill collars to 3m in XYZ is usually sufficient accuracy for the initial exploration drilling.  Once there is a discovery drill hole, project focus shifts to the confirmation and delineation of inferred resources.

 

When drilling to delineate resources after a discovery drill hole, you need better than 50cm survey accuracy.

Once the focus of the drilling campaign shifts to confirmation and delineation of inferred resources, survey quality topographic accuracy is required for the project. This is accuracy of better than 50cm in XYZ for drill hole collar locations and the locations of surface samples and trenches.

 

First, establish a survey benchmark with GPS.

The first and most important step in accurately surveying an exploration project is establishing a survey benchmark that is accurate to better than 10cm in easting, northing and elevation. The most reliable way of establishing an accurate survey benchmark is to record 12 hours of GPS signals with a dual frequency geodetic quality GPS receiver. PhotoSat provides guidelines for establishing survey benchmarks.

Mining project survey benchmark with the coordinates, horizontal projection, horizontal datum and vertical reference listed on the plaque.

 

GPS survey the drill hole collars, trenches and ground control targets.

The drill holes, trenches and at least three ground control targets should be surveyed with differential GPS.  For differential GPS surveys, the GPS signals at the benchmark, and the survey point must be recorded at the same time.  Many of the survey points can be surveyed while the benchmark survey is being recorded for 12 hours. The GPS signals at each of these survey locations should be recorded for at least 30 minutes plus one minute for each kilometer of distance between the survey benchmark and the survey location.

 

LiDAR, PhotoSat or Drone topographic survey of the project area

Depending on the size of the area, vegetation cover and location survey the project area to an accuracy of better than 50cm in elevation with airborne LiDAR PhotoSat or a Drone survey. The advantages of the different survey methods are discussed in a PhotoSat surveying white paper Comparison of PhotoSat, LiDAR, GPS and Drone surveying.

This survey will provide the topographic surface needed by the mining engineers preparing the reserve and resource volume calculations for your Preliminary Economic Assessment (PEA).

1m elevation contours and the locations of drill holes on the Almaden Ixtaca mining exploration project.

 

3D satellite image of the Almaden Minerals Ixtaca project showing drill hole locations and the discovery drill hole.

For more information, see the following:

Satellite Surveying
Mining Exploration
How accurate is PhotoSat surveying?
Accuracy Studies

mine tailings beach profile

Measure your mine tailings beach lift thicknesses, slopes and profiles from space

By Gerry Mitchell, P.Geo, President PhotoSat

mine tailings beach profile

Satellite photo of a mine tailings beach

Mine tailing beach designs have optimum slopes.

Every mine site tailings storage facility (TSF) design includes optimum slopes for the tailings beaches. Tailings beaches that are either steeper or flatter than the designed slopes can have serious short-term and long-term consequences for the capacity and cost of the TSF.  Tailings engineers control the beach slopes by modifying the composition of solids and fluids discharged into the TSF in each lift.

Detailed information on tailings beach slope design and the consequences of different beach slopes can be found on the Tailings.info website.

Elevation image of a mine tailings beach with 50cm elevation contours on the tailings beach surface.

Elevation image of a mine tailings beach with 50cm elevation contours on the tailings beach surface.

Semi consolidated tailings beaches cannot be accessed by conventional surveying.

Measuring and monitoring the tailings beach slopes are challenging.  Since the tailings beaches are semi consolidated, they cannot be safely accessed by conventional surveying methods. 

 

 

Suncor review of tailings storage facility surveying methods found PhotoSat most cost effective.

In 2014 Paul Lomond, lead surveyor for the Suncor Steepbank and Millennium oil sands mines, published a review of a pilot project assessing various methods of surveying tailings storage areas.  This review is available on the Suncor tailings surveying page.  Suncor concluded that PhotoSat surveying is the most cost effective method for surveying their tailings beaches.

 

Incremental tailings thickness (isopach) surveys

In order to control the tailings beach slopes, mine site tailings engineers need to be able to determine the actual distribution of tailings on the tailings beaches.  Images showing the increase in elevation of the beach surface between two dates show the tailings engineers the actual distribution of the tailings over the time period. 

Increase in mine tailings beach height over a three month period.  25cm contours of tailings thickness.

Increase in mine tailings beach height over a three month period. 25cm contours of tailings thickness.

Mine tailings beach profiles from PhotoSat surveys

Mine tailings beach profiles from PhotoSat surveys

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

Mining

Mine site volume reconciliations

Mine Leach Pad & Ore Stockpile Volumes

Mine Tailings Surveying

Mine Site Toes & Crests

 

 

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, 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).  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 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 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.

 

 

 

 

 

satellite photo of a tailings beach.

Improving Safety for Mine Survey Teams: How Ground Surveying Fits Seamlessly With Satellite Topography

Mine survey teams perform a job that’s increasingly vital, increasingly technological – and more dangerous every day. When they’re doing preliminary work to acquire geophysical data for exploratory purposes, or scouting out pit placement, they’re subject to dangers including rockfalls and environmental dangers that can include severe weather and wild animals. Many mine sites are in inaccessible locations, in rugged terrain far from habitation, where it’s hard to put teams and even harder to get them out again fast when someone gets hurt.

At the same time, the industry is expanding into new regions where mining has previously been carried out with pick and shovel or even literally by hand. In sometimes socially-volatile places where old mine workings don’t show up on maps that are often themselves inaccurate, mine survey teams are saving the lives of miners by supplying engineers with accurate data – but they’re endangering their own safety to do it.

And what about when ground survey teams visit a working open mine to check for bench integrity? They’re sharing their working environment with heavy trucks and putting themselves in the way of slumping bench walls and falling debris.

PhotoSat’s 30cm accuracy satellite topography can provide a solution by filling in part of the puzzle. Mine survey teams will always be needed, but their exposure to risk should be minimized. When you get your elevation data from LiDAR or GPS, it can be significantly slower than PhotoSat’s unique geophysical processing technology. You’ll typically wait weeks, especially for aerial LiDAR. PhotoSat usually provides a client with engineering quality elevation mapping within 5 days, and there’s no boots on the ground so safety risks are minimized.

That doesn’t mean ground survey teams, LiDAR or other scanning technologies are redundant. Just look here to see how one of our clients, Suncor, combines multiple scanning technologies to get the data they need.  In 2014, Suncor and PhotoSat presented on the benefits of incorporating satellite surveying into their survey process for their Tailings Reduction Operation (TRO). With many areas of the TRO cells inaccessible to ground surveyors, the satellite-based technology reduced exposure to hazards.

But it does mean there’s a way to get a fast, engineering quality mine survey that can be used for multiple engineering and planning applications – without putting anyone in harm’s way.

To find out more about PhotoSat’s 30cm accuracy satellite topography for mine surveys, contact us at info@photosat.ca or 604-681-9770.

satellite photo of a tailings beach.

High resolution satellite photo of a tailings beach.

elevation image of a tailings beach

PhotoSat elevation image of a tailings beach

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