Comparing the theoretical performances of 1.65- and 3.3-μm differential absorption lidar systems used for airborne remote sensing of natural gas leaks

Abstract. Airborne remote sensing approaches to natural gas leak detection have recently become a viable alternative to traditional in situ surveillance methods. However, there have been few formal studies addressing the advantages and disadvantages of the various kinds of instruments typically employed for this purpose. This investigation compares the theoretical performances of differential absorption lidar systems operating near 1.65 and 3.3  μm. The random errors affecting these instruments’ respective retrievals were simulated over a range of aircraft altitudes and observed natural gas concentrations. It was found that the 3.3-μm system is capable of measuring smaller leaks with less error than the 1.65-μm system but only when flying at lower altitudes. The noise floors of the 1.65- and 3.3-μm instruments simulated in this particular analysis are ∼1.4 and ∼0.1  ppm m, respectively. However, when flying at altitudes >∼220  m or observing leaks with concentrations >∼500  ppm m, the 1.65-μm system exhibits better precision than the 3.3-μm system. These results demonstrate that it may be more appropriate to employ one instrument over the other depending on the surveillance scenario at hand.