The Basics of Optical Gas Imaging
Optical gas imaging (OGI) cameras are powerful handheld scientific instruments that are used in the oil and gas sector to locate leaks and emissions, including methane, that are released into the atmosphere. These gases contribute to air pollution, climate change, safty issues and sometimes conditions that cause and/or contribute to human adverse health effects.
While there are many sources of methane pollution, the oil and gas industry is the largest industrial source of methane pollution, and by far the source that is most easily remedied.
The camera we’re using
We are using a FLIR GF320TM to document these emissions.
First used by regulators and industry in 2005, handheld OGI thermal imaging cameras have the special ability to make invisible hydrocarbon vapors visible and recordable. Though more traditional ambient air monitoring technologies such as sniffer instruments, real-time monitors, and discrete air samples allow the user to measure pollutant concentrations, OGI remote sensing cameras allow us to visualize emissions that are invisible to the human eye.
How it works
FLIR GF320 optical gas cameras have proven to be an effective tool in pinpointing air emission sources through the measurement of infrared energy. Infrared energy is a part of the electromagnetic spectrum and behaves similarly to visible light.
Though the human eye can detect visible light, it cannot detect any of the other electromagnetic wavebands. However, other specialized equipment can receive, process, and characterize different energy types like the microwave in your kitchen, the x-ray machine in your physician’s office, the radio in your car, and the television in your home.
In the case of infrared energy, it lies between visual light and microwaves in the electromagnetic spectrum. Since all objects above absolute zero emit infrared radiation, the GF320 camera can detect the energy exchange between objects and surfaces in a hot to cold direction. Depending on what they are constructed of, some objects retain heat longer than other objects.
Besides the ability to measure and detect heat differences, the GF320 contains a special filter that allows it to detect infrared energy in the 3.2 – 3.4 micrometer waveband. In addition to methane, other hydrocarbon gases of interest have infrared energy transmittance in this range (see FLIR’s list of common hydrocarbons and VOCs detected by this camera). The ability to visualize these VOCs and greenhouse gases is an important aspect in minimizing emissions that cause and contribute to climate change.
Documentation of Sites
Every time we visit a site to document emissions we take extensive notes about our field activities including collecting digital photographs that can be compared to the OGI images. This helps us effectively interpret field findings including both hydrocarbon and steam plumes from a variety of emission sources including but not limited to industrial stacks, flares, storage tanks, separators, pipelines, et cetera. We also note the time of day, GPS coordinates, and meteorological data.
The GF320 has a range of color palettes to help the user visualize the gas plume. The color palettes show the range of temperatures detected by the camera. Greyscale is the primary color palette often used to show infrared imagery.
The three images below are shown in various versions of greyscale. The greyscale color palette can be shown as black-hot, with black representing the highest temperature; white-hot, with representing the hottest temperature; or high sensitivity mode (HSM), an internal image analyzer that helps identify a gas plume.
You may see us use other color palettes that are available with the FLIR GF320 camera, as shown below:
Successful Gas Detection:
To effectively visualize emissions, we need at least a 2-degree Celsius temperature difference between the emission plume and the background surface, whether it be the sky, a tree, or a storage tank. In addition, we need to ensure plume movement via the emission source itself or winds also assist in detecting hydrocarbon plumes during field projects.
Despite the amazing technical power of this technology, the gas camera is not a magic box. There are four primary conditions that must be met.
1- A leak is present
This seems obvious, but in order to see a leak there must be a large enough leak to observe. The camera is quite sensitive and can see very small leaks. In the laboratory conditions, the GF320 can detect 0.6 g/hr of methane. from less than 5 meters. However, just because we don’t see a leak or emissions at a site, it does not mean that hydrocarbons are not being actively released, as other conditions (see below) are also crucial to seeing a leak.
2- Getting ideal ambient conditions
It is a user-friendly scientific instrument that can be used to detect hydrocarbon gases when used by a skilled operator in the right ambient conditions. Since moisture affects/prevents the transfer of infrared energy through the atmosphere, this technology is not typically used during rainy, snowy, or foggy conditions. It can be effectively used in both cold and warm weather, though strong and gusty winds may lead to false negatives as emissions are difficult to see in these conditions.
3- Getting close to the source and getting the right angle
Field and geographic conditions can affect our ability to detect emissions. This can include logistical limitations such as roadways that are too distant from our target location or increased security measures that keep us away from the site. We could also experience more technical limitations, such as the angle of the sun in relation to the emission source or a hot object that lies beyond the emission source and interferes with ability to see the plume.
4- Experience of the User
In addition, our technical abilities and self-motivation also have much to do with detecting and visualizing hydrocarbon emissions. We must make technical adjustments to the GF320 including but not limited to proper camera focus, auto/manual/high sensitivity modes, temperature ranges, and color palettes. That is why we have invested through the FLIR Infrared Training Center and are certified in optical gas imaging.