- The working principal of both ALMA and SELMA is based on a beam from a pulsed diode laser beam which is directed at the pipeline or facility to be inspected.
- The laser's wavelength of 1.65 um corresponds to the first absorption frequency of methane.
- The laser beam which is targeted at the pipeline is reflected and the scattered reflection is collected by the recieving mirror.
- A photo detector generates a signal which is compared to the signal from a reference channel (a laser beam through a curette with a standardized gas sample).
- When methane is detected the laser light will be absorbed and the deformation of the signal is proportional to the concentration of methane along the measuring path.
- Windows based software allows for the integration and anlysis of all the data including GPS signal, video images, infrared data and mapping information to produce post leak survey reports.
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