A ground-based, integrated path, differential absorption (IPDA) light detection device capable of measuring multiple greenhouse gas (GHG) species in the atmosphere is presented. The device was developed to monitor greenhouse gas concentrations in small-scale areas with high emission activities. It is equipped with two low optical power tunable diode lasers in the near-infrared spectral range for the atmospheric detection of carbon dioxide, methane, and water vapors (CO₂, CH₄ and H₂O). The device was tested with measurements of background concentrations of CO₂ and CH₄ in the atmosphere (Crete, Greece). Accuracies in the measurement retrievals of CO₂ and CH₄ were estimated at 5 ppm (1.2%) and 50 ppb (2.6%), respectively. A method that exploits the intensity of the recorded H₂O absorption line in combination with weather measurements (water vapor pressure, temperature, and atmospheric pressure) to calculate the GHG concentrations is proposed. The method eliminates the requirement for measuring the range of the laser beam propagation. Accuracy in the measurement of CH₄ using the H₂O absorption line is estimated at 90 ppb (4.8%). The values calculated by the proposed method are in agreement with those obtained from the differential absorption LiDAR equation (DIAL).

The technical specifications and the evaluation of the remote operation of the open-path, tunable diode laser absorption spectroscopic (TDLAS) instrument are presented. The instrument is equipped with two low optical power diode lasers in the near-infrared spectral range for the atmospheric detection of carbon dioxide, methane, and water vapors (CO₂, CH_4, and H₂O). Additionally, the instrument eliminates the requirement of retroreflectors since it detects the back reflection of the laser beam from any topographic target. The instrument was operated remotely by measuring background concentrations of CO₂ and CH₄ in the atmosphere from 24 November 2022 to 4 January 2023. The accuracy of CO₂ and CH₄ measurement retrievals on a 200 m laser path was estimated at 20 ppm (4.8%) and 60 ppb (3.1%), respectively. The CH₄ accuracy is comparable, but the CO₂ accuracy is noticeably lower than the accuracy achieved in local operation. The accuracy issues raised are studied and discussed in terms of the laser driver’s cooling performance.

A method to measure long-range distances (>100 m) using a continuous-wave laser is presented. A continuous-wave laser beam at a wavelength in resonance with the water vapour absorption lines of water vapours at 1.52 μm is propagated to an object at a distance of 750 m, and the back-reflected signal is recorded. The atmospheric parameters (vapour pressure, temperature, atmospheric pressure) were recorded simultaneously with the laser back-reflection measurements. The water vapour concentration in the atmosphere is calculated from the atmospheric parameters. The distance from the laser sensor to the object is calculated using the differential absorption lidar (DIAL) method and the water vapour concentration. A 22 h experiment was performed to validate the methodology effectiveness during diurnal weather variation. Two water vapour absorption lines were used to calculate the distance to the object. The calculated distances were found to be 730 m ± 20 and 720 m ± 30 (2.7% and 4.0% deviation, respectively, compared to the actual distance).