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.

Tailings dyke elevation image number 2.

Monitoring Tailings Dykes with Satellite Elevation Data

In both the oil sands and mining industries, the integrity of tailings dykes is extremely important. Recent tailings incidents demonstrate this. Mapping the tailings dykes and beaches can be challenging with hazardous conditions restricting access for ground surveyors. Using satellite-based elevation mapping allows for data to be collected remotely, with no risk for ground personnel and no permits needed. Regular topographic mapping during construction allows the design engineers to confirm that the dykes are being built to design specifications.

Currently PhotoSat regularly surveys the topography of tailings dykes for the Alberta oil sands mines to an accuracy of 15cm in elevation. In fact, we map the entire tailings systems for Suncor’s Millennium and Steepbank mines about every two weeks. These surveys are used by a wide range of engineers and planners at Suncor. They even did a presentation about their experience comparing different survey options and why they settled on PhotoSat’s technology as their main topographic survey method.

Tailings dyke elevation image

Elevation image of a tailings dyke, December. Red is high, blue is low.

Tailings dyke elevation image number 2.

Elevation image of the same tailings dyke 6 months later. Red is high, blue is low.

Unique Methods for Elevation Mapping

Satellites can collect imagery anywhere in the world, and with new high resolution satellites being launched regularly, there are more options and collection times keep getting faster. Also, PhotoSat has a unique, automatic system for processing stereo satellite imagery to extract the bare-earth elevation values. That’s right – we invented this process ourselves here in Vancouver, and continuously improve the system to get better and better accuracy results. Additional information about the technology we use can be found on the Technology page. And we test our system regularly by publishing accuracy studies that are available on our website here.

We also survey all parts of tailings projects beyond the dykes for a complete profile of a mine site tailings area, including the sand dumps, tailings beaches, and mature fine tailings. The advantage of satellites is that they can collect imagery over a large area in one shot, providing an instantaneous snapshot of the entire tailings beach waterline, the geometry of the beaches, and the height of the tailings dykes. Areas from 100-200 sq km can be collected in one satellite pass.

Our standard elevation accuracy specs for mining projects is better than 30cm, and you can find out more about our digital elevation data package here. If even higher accuracy is required, contact us as we often can provide higher accuracies depending on the project.

To find out more about our engineering grade satellite topography, contact us at info@photosat.ca or 1-604-681-9770.

Mexico onshore oil and gas blocks

High Accuracy Surveying and Satellite Photos for Mexico Round 1 Onshore Blocks

As you probably already know, Mexico’s oil and gas blocks are up for auction and the next round includes the onshore fields. For bidding companies, detailed satellite elevation mapping and high resolution ortho photos can significantly help understand and assess the surface topography.

View the brochure for Mexico blocks satellite data (PDF).

Mexico onshore oil and gas blocks

Mexico onshore oil and gas blocks for bidding

 

PhotoSat can provide 30cm vertical accuracy, 1m bare earth elevation grids (DEM) for all blocks. These DEMs are produced from archive satellite images.

The benefits of having high accuracy surveying include:

  • Assessing environmental conditions including drainage and flood risk assessment.
  • Engineering grade accuracy allows for accurate assessments of the location of existing infrastructure (well sites, roads, pipelines etc).
  • Knowledge of the ground conditions reduces risk.

If the available satellite images used to produce the topographic data are too old for your purposes, we can acquire new satellite images on request. Contact us at info@photosat.ca for information on the data available over the block in question, and for pricing.

We can accommodate custom coordinate systems and are able to use many types of surveys for ground reference points. We can also produce the mapping without ground control points if nothing is available. More information on our 30cm accuracy satellite elevation mapping can be found on our main website.

If detailed base mapping is not required yet, we can also provide high resolution satellite ortho photos only over the desired block.

The following table outlines the existing 50cm resolution satellite images that are immediately available for all blocks. Included are the size of the block and the most recent ortho photo date. If you need more current information, we can task a satellite to collect new images.

Campos Burgos:
Block Size (sqkm) Archive ortho image date
Anahuac 30 October 2014
Duna 37 March 2014
Mareografo 30 March 2014
Calibrador 16 March 2014
San Bernardo 29 November 2013
Benavides 136 November 2013
Pena Blanca 26 June 2015
Carretas 90 November 2013
Ricos 24 August 2013
Campos Norte:
Block Size (sqkm) Archive ortho image date
La Laja 10 July 2014
Ponton 12 August 2015
Paso de Oro 23 October 2014
Tecolutla 7 January 2014
Barcodon 11 March 2015
Campos Sur:
Block Size (sqkm) Archive ortho image date
Moloacan 47 June 2015
Calicanto 11 May 2015
Cuichapa Pte 42 June 2015
Mayacaste 22 April 2015
Tajon 28 April 2015
Paraiso 17 April 2015
Fortuna Nacional 22 June 2015
Mundo Nuevo 28 May 2015
Topen 26 May 2015
Catedral 58 May 2015
Malva 22 May 2015
Secadero 10 May 2015

 

Our standard delivery is an ortho photo centered on each block covering 100 sq km. Pricing is based on the square kilometer, and custom sizes and shapes are available on request.

View the brochure for Mexico blocks satellite data (PDF).

Feel free to contact us for a quote, or for any questions: info@photosat.ca, 604-681-9770.