Trustworthy technology for the monitoring of fugitive methane emissions is an indispensable component for low−carbon emission reduction and safe production in oil and gas infrastructure. A miniaturization and low-cost methane remote monitoring prototype based on near-infrared laser absorption spectroscopy is developed to retrieve the path−integral concentration by employing the harmonic conjoint analysis method for the backscattered echo signals from a distant non-cooperative target. A distorted harmonic template matching (DHTM) algorithm is proposed based on wavelength modulation spectroscopy with second harmonic normalized via the first harmonic (WMS−2f/1f) method, which suppresses the output concentration fluctuation caused by open path monitoring with non-cooperative target and avoids the issue of false alarms during the detection process without target gas. The reliability of the WMS−2f/1f−DHTM algorithm is verified by calibration and dynamic experiments. The results showed that this algorithm avoids the dilemma of false alarms in the absence of gas compared to the conventional WMS−2f/1f algorithm, while the root mean square error (RMSE) of the concentration inversion with a detection distance of 20 m is reduced by 57.6% compared to direct absorption spectroscopy (DAS) algorithm. And the minimum detection limit of system is 3.79 ppm·m. The methane telemetry sensor with the WMS−2f/1f−DHTM algorithm exhibits substantial application potential in carbon monitoring of oil and gas industry.

Observing the vertical diffusion distribution of methane fugitive emissions from oil/gas facilities is significant for predicting the pollutant’s spatiotemporal transport and quantifying the random emission sources. A method is proposed for methane’s vertical distribution mapping by combining the laser path-integral sensing in non-non-cooperative open paths and the computer-assisted tomography (CAT) techniques. It uses a vertical-plume-mapping optical path configuration and adapts the developed dynamic relaxation and simultaneous algebraic reconstruction technique (DR-SART) into methane-emission-distribution reconstruction. A self-made miniaturized TDLAS telemetry sensor provides a reliable path to integral concentration information in non-non-cooperative open paths, with Allan variance analysis yielding a 3.59 ppm·m sensitivity. We employed a six-indexes system for the reconstruction performance analysis of four potential optical path-projection configurations and conducted the corresponding validation experiment. The results have shown that that of multiple fan-beams combined with parallel-beam modes (MFPM) is better than the other optical path-projection configurations, and its reconstruction similarity coefficient (ε) is at least 22.4% higher. For the different methane gas bag-layout schemes, the reconstruction errors of maximum concentration (γ_m) are consistently around 0.05, with the positional errors of maximum concentration (δ) falling within the range of 0.01 to 0.025. Moreover, considering the trade-off between scanning duration and reconstruction accuracy, it is recommended to appropriately extend the sensor measurement time on a single optical path to mitigate the impact of mechanical vibrations induced by scanning motion.