Influence of Update Rate on the Susceptibility of Standoff Open-Path TDLAS Measurements to Drone-Induced Mechanical Noise

Tunable diode laser absorption spectroscopy (TDLAS) is a well-established spectroscopic method used for remote gas concentration measurements in real-world environments. However, mechanical vibrations affecting optical components exposed to environmental conditions can limit the precision of these measurements. In this work, we experimentally demonstrate that precompensating the current modulation to enable rapid switching between two or three wavelengths reduces the integration time required to achieve a “frozen scene,” i.e., a state effectively free of mechanical vibration effects. This improvement was demonstrated by analyzing the overlapping Allan deviation of CO2 measurements under atmospheric conditions (approximately 430 ppm) as a function of the instrument’s update rate, which ranged from 156 Hz to 30.86 kHz, achieving the fastest real-time remote TDLAS concentration measurements reported to date. The experimental setup included a drone-mounted retroreflector, and the Allan deviation was characterized both with the drone turned off and on while clamped to a stage. We observed that increasing the measurement frequency reduced the integration time required to freeze the scene, but the limited speed and resolution of the electronics used meant an optimal working point of 15.43 kHz for our configuration. Lastly, this characterization served to select the update rate to utilize during an outdoor measurement which confirmed the usefulness of the high update rates in the suppression of the effect of drone-induced mechanical noise on concentration measurements.