Methane Gas Detection: Thermal vs Laser

by

Methane Gas detection sensors: THERMAL vs LASER ?

 
The question frequently asked is, which is better, thermal or laser sensor for UAV based methane gas detection?
 

How does a laser gas detector work?

Utilizing laser technology, gas leaks are located by pointing the laser beam towards the suspected leak, or along the survey line. The laser beam directed at targets such as gas piping, the ground, etc., will reflect back a diffused beam from the target. The device will receive the reflected beam and will measure the absorptivity of the beam, which will then be calculated into methane column density (ppm-m).
 

How does a thermal camera for gas leak detection work?

If a thermal camera reads a scene without gas leak, objects in the angle of view will radiate and reflect infra-red radiation that will react through the lens and the filter on the detector. The filter only lets some wave lengths of radiation enter the detector from which the camera generates not compensated image of radiation intensity of the radiation. If there is a cloud of gas between the lens and thermal camera, this gas will selectively absorb radiation to the extent of its spectral absorption and the amount of radiation passing through the gas which affects the detector will be lower.
 

A brief comparison

The laser detector allows gas hot-spots to be detected only at locations in a narrow field of view of the “one point”. The thermal camera, on the other hand, makes it possible to detect and measure hot-spots in the entire image which it is able to observe with its lens.
 
As an example, a GIS-320 thermal camera allows visualization and therefore detection of gas leaks on large areas due to the relatively large field of view (see the table below) and the large number of detectors. This is not only one (as with the laser methane detector), but with a resolution of 320×240, there are 76,800. Thanks to this, it is possible to scenario even very large areas.
Methane Gas detection

During a one flight, you are able to control about 150m x 150m (at an altitude 80 m) area or about a pipe line up to 1000 m in length.

The following table records in more detail the differences between the two types of sensors against a broad array of dimensions:

Table

 InfraredLaser
Spectrum
  • the infrared sensor achieves rather weak resolution.
  • spectral resolution a factor 1’000 weaker
  • overlapping gas absorption bands a serious problem to  IR detectors – particularly with water absorption bands
  • the high resolution approach of the laser detectors makes resolution a non-issue, resulting in Zero Cross-Sensitivity.
Long term Stability
  • And light source of infrared sensors is just similar to that of light bulbs, as time going on, it will become weaker
  • Laser sensor modules adopt the most modern and stable semiconductor photoelectric components and have a long service life.
Single Channel stability
  • infrared sensor detectors need a second measurement channel as reference to avoid deterioration over the long term
  • no need for a reference channel or frequent calibration routines
Power consumption
  • NDIR detector uses electrical power to generate a broad spectrum of intensities
  • therefore uses only a tiny fraction of the emitted light, leaving the main portion of the used electrical power wasted
  • laser detector emits 100% of its light at exactly the wavelength of interest
Principle technology
  • infrared sensor use infrared light source and filter technology.
  • uses near-infrared laser technology,
  • laser type methane sensors response quicker and with anti-wet and anti-vibration capacity and more stable during working operations
Response time
  • light source of infrared sensors is infrared radiation which is from the heating special ligament. Only little effective light in infrared radiation could be used. Therefore it takes a long time to integrate to test the effective signal and makes a slower response speed (more than 30s).
  • response time of laser type methane sensors is a 1000ms
Humidity
  • water molecular has a strong absorption characteristics in the infrared district (therefor inferior)
  • infrared sensors are weak in light source signal, usually a difference needs to be done between standard gas chamber and detection gas chamber to find out the effective signal, thus gas chamber should be with complex structure, weak anti-vibration capacity
  • laser sensors from trigger no response towards vapour and are with excellent anti vibration capacity

 

Detectable gases:
  • 100+ different gases
  • single gas (e.g. methane)
Type of measurement:
  • image stream
  • spot measurement
Detection:
  • gas propagation and leakage source
  • presence of gas
Typical application:
  • whole area scanning
  • spot measurement or liner inspection

In summary.

Infrared sensors may have the ability to detect a wider range of gases over a wider area but, require the operator to CONSTANTLY MONITOR the image stream.
Laser sensors, which are much sharper with a quicker response, can automatically detect the relevant gas and, in conjunction with infrared and optical cameras, then take both a visual and a thermal snapshot of the identified leak.
 
 

Remote Laser Gas Detector

The Remote Laser Gas Detector UAV can efficiently and rapidly detect methane gas from 30 meters away. This allows for accurate remote sensing on a UAV platform. With the fast detection rate, a UAV can rapidly cover a large area allowing for quick and efficient pipeline inspections.