Modelling and interpretation of gas detection using remote laser pointers

Abstract

We have developed a quantitative model of the performance of laser pointer style gas leak detectors, which are based on remote detection of backscattered radiation. The model incorporates instrumental noise limits, the reflectivity of the target background surface and a mathematical description of gas leak dispersion in constant wind speed and turbulence conditions. We have investigated optimum instrument performance and limits of detection in simulated leak detection situations. We predict that the optimum height for instruments is at eye level or above, giving an operating range of 10 m or more for most background surfaces, in wind speeds of up to 2.5 ms(-1). For ground based leak sources, we find laser pointer measurements are dominated by gas concentrations over a short distance close to the target surface, making their readings intuitive to end users in most cases. This finding is consistent with the results of field trials.

Optical gas sensing: a review

“…Laser pointers preferentially sample the gas in a thin layer close to the ground in a highly localised area downwind of the leak source [257] . For this reason, the correspondence between the standoff measurement and that of a point sampling instrument is surprisingly good, as Figure 45 shows.…”

“…Correspondence between field measurements from a prototype laser pointer and flame ionisation detector (FID) targeted at the same sampling location, taken during a release of natural gas at 10 litre min -1 . Taken from [257].…”

Small unmanned airborne systems to support oil and gas pipeline monitoring and mapping

“…Differential absorption Lidar (DIAL) technology , currently operating on manned helicopters, beams and records light pulses of two different wavelengths-the measurement wavelength is absorbed by the gas (if present) whilst the reference wavelength is not. On-board UAVs, laser gas detectors can detect (Horn 2016) and provide accurate measures of gas leaks (Hodgkinson et al 2006), although they have an inherent disadvantage of small sampling capacity (Bretschneider and Shetti 2015). Gas (methane) cameras enabling visualization of the gas presence might be useful for identification of pipeline leakages; the adaptation of these sensors to small-scale flying platforms has still to be realized.…”

Untitled

“…For that reason, the use of generic and directed software has increased in the last decade, especially with the exponential growth of data provided by next-generation DNA sequencing (NGS) Chawla S et al (2016). This situation has created numerous challenges associated with the treatment, storage and analysis of information Hodgkinson et al (2006).…”