Catching The Wavelength
- Category: Archived News
- Published: Saturday, 30 August 2014
Company calibrates field spectrometry to satellite imagery for remote monitoring
The colour spectrum is but a mere fraction of the total range of possible electromagnetic radiation wavelengths, and what a combination of field and orbital spectroradiometer readings can detect provides the energy sector with a powerful tool for environmental monitoring and reclamation, going far beyond what the human eye can see.
Since 2012, Golder Associates Ltd. has used this application of field spectrometry for radiometric calibration of multispectral satellite imagery to help gather data on vegetation and soil as part of a multi-year, multidisciplinary monitoring project for Shell Canada Limited’s Quest carbon capture and storage project, which is on schedule to start capturing carbon in 2015.
“The objective of the whole project from Golder’s perspective is to document the pre-injection baseline conditions of the hydrosphere and biosphere,” Davor Gugolj, remote sensing and GIS analyst with Golder, told the Petroleum Technology Alliance Canada 2014 Geospatial Monitoring and Analytics Forum in April.
“My part, as the remote sensing component, is to gather spectral data for atmospheric correction of multispectral satellite imagery, and also to compile a spectral-data library or database of various land cover types that are existent in the area of interest, establishing the baseline conditions in the project area.”
Spectrometry is the study of interaction between matter and radiated energy. The sun emits radiation on a wavelength spectrum that impacts objects on Earth. Some of that radiation is absorbed, some is scattered or refracted and some reflected. Just as an eye can detect visible colours, different instruments can detect various other wavelengths on the spectrum that can provide information about an object. A spectral response curve, or spectral signature, is like a fingerprint—it shows a pattern of how the object reflects or absorbs specific wavelengths.
Gugolj tells New Technology Magazine, “What we are mostly concerned with is the incident energy that is reflected off of the object.”
For example, he says, when looking at a natural grass field versus an artificial turf field, both may appear identically green to the naked eye. However, if analyzed in the near infrared, the more-absorbent turf appears darker, whereas the less-absorbent grass appears brighter.
According to Gugolj, while satellites are essentially mounted with powerful spectroradiometers, there is a lot of atmosphere between orbital space and the Earth’s surface, impacting the radiation reflected back into space. Therefore, Golder calibrates those broader satellite images with detailed samples from the target area collected on the ground.
“With just the [satellite] imagery, we can’t make many detailed inferences about the landscape. What we need to do is perform radiometric calibration, or atmospheric correction, using different methods.
“One of those methods is by obtaining field radiometric spectrometry data. We will then correlate the values found in the [satellite] image with values found in the field, and therefore we can get a better understanding of what is actually on the ground, and we can actually get a shot of it across the whole landscape with that calibrated image.”
Gugolj says that for the field component of this process, his team takes numerous samples of different landscapes using a spectroradiometer, measuring those values against the satellite image at a particular point, thus enabling correlation.
About the size of a consumer camera, the field spectrometer is simply pointed at various objects to measure the amount of energy that bounces off of it. Gugolj says field spectrometry is nothing new, but it is becoming more accessible as the size of the instrument shrinks.
“In the past, it used to be a full-sized backpack, along with this thing that was the size of a [tower computer]. It would take an hour to warm up, and you would have to hook up a laptop to it and go out in the field with this contraption. Obviously, it is much, much easier when it is the size of a camera, and it also doesn’t cost $50,000 now, but more like $4,000 or $5,000.”
Unfortunately, capturing field data still requires getting on top of sometimes-difficult geologies or vegetation, such as wetlands or tree canopies. Fortunately, Gugolj says, as the technology becomes more portable, the potential for placing spectroradiometers on an unmanned aerial vehicle becomes more feasible, allowing for better access than is currently the case for a time-tested method of data collection.
“It’s an old technology. While it is used in academia, there are applications, and some of them could be identification of different geological features, different types of rocks and minerals.... We can also do assessing of water quality, for example, by just looking at different suspended sediments. It can be used for many things.”
Despite the benefits, Gugolj says the industry is largely unaware of how field spectrometry can be used for essentially any sort of industrial development.
“What we could do for clients is [assist in] baseline studies, which consists of going out there and assessing the environment as a reference point before any development happens,” he says, adding Golder can use its field equipment to enable monitoring of conditions in a particular area before, during and after development, showing how vegetation is responding to changing circumstances.
“Once the image is calibrated, what we can essentially do is interpolate those values across the [satellite] image, and then we can tell without going to every single spot what those areas are, based on our groundwork.”
While the technology would not be applicable to actually discovering hydrocarbon deposits underground, Gugolj says there is a tremendous industry potential in regard to environmental monitoring and reclamation. At Quest, Golder is identifying various injection-phase monitoring approaches and developing possible leak-detection methods for the northern Alberta project.
“One thing we could do is assess how well certain areas are doing, and if those are healthy [relative to baseline]. There are other ways of doing it by sending out crews and checking things out, but this is one of the ways that could be done as well.”
According to a Shell spokesperson, the company is using Golder’s multispectral image analysis calibrated with field spectra surveys in order to verify the absence of CO2 in the region once Quest injection begins.
Shell is currently evaluating the ability of this methodology to correlate anomalous changes from the remote sensing data to the calibrated soil and vegetation profiles, assessing its capability to detect any environmental changes potentially associated with Quest, which is important considering extensive agricultural activities in the region.
The Quest monitoring plan currently includes technologies such as laser-based atmospheric CO2 monitoring, remote sensing, groundwater well monitoring, time-lapse vertical seismic profile and surface seismic, as well as satellite-based ground deformation monitoring. Subsurface monitoring will include injection wells, deep observation wells and groundwater wells.
CONTACT FOR MORE INFORMATION
Davor Gugolj, Golder Associates Ltd.
Tel: 403-509-1856
Email: [email protected]
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