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[Institution of Engineering and Technology 20th Italian National Conference on Photonic Technologies (Fotonica 2018) - Lecce, Italy (23-25 May 2018)] 20th Italian National Conference on Photonic Technologies (Fotonica 2018) - Detecting the influence of water vapour on the measurements of minor chemical gases with the Differential Absorption LIDAR technique
摘要： The monitoring of pollution is fundamental to guarantee the health and the safety of the environment and humans. In fact, pollution is strictly correlated to climate changes, acid rains and in disease occurrences. The Differential Absorption LIDAR (DIAL) is a remote sensing technique able to identify the chemical substances in the atmosphere. This method is able to give information along long distances (also larger than 1 km) and it is possible to provide the system with equatorial mounts, in order to extract areal or volumetric concentration field. In this work, the authors focus on the interaction of water vapour with minor chemical gas measurements. In fact, the DIAL equation is achieved assuming some hypothesis that could not be acceptable in any conditions. In the present paper is evaluated how water vapour could change the differential extinction coefficients and when influences the final measurements. Both analytical investigation and experimental measurement are provided. These methodologies have been applied to six pollutants: ammonia (NH3), Benzene (C6H6), Nitrogen Dioxide (NO2), Nitrous Oxide (N2O), Ozone (O3) and Sulphur Dioxide (SO2).
关键词： DIAL,LIDAR,Water Vapour,Minor Chemicals,Measurements
更新于2025-09-23 15:21:01
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Atmospheric CO <sub/>2</sub> -Detection Via Scheimpflug DIAL Employing a Simple Fiber Amplifier
摘要： The ever-increasing worldwide environmental awareness has prompted much effort to minimize humanity’s ecological footprint. This has led to increased demands for reliable technologies for assessing the current situation as well as the efficiency of new policies and interventions. In particular, CO2-monitoring has attracted lots of attention as CO2 is the greenhouse gas that is emitted in the largest quantities. Differential absorption light detection and ranging (DIAL) is a well-established method for measuring the atmospheric CO2-concentration. Conventional implementations of this method rely on tunable pulsed laser sources whose back-scattering at different distances are compared for different wavelengths, corresponding to being on and off the CO2-resonances, to calculate the concentration along the measured path. Integrating these types of laser sources with DIAL systems have proven to be complicated and often suffer from instabilities. Therefore, a continuous-wave DIAL (CW-DIAL) scheme was recently proposed that relates signals at different distances to different points on a detector by using a Scheimpflug configuration. This technique relies on a rapidly tunable, narrow-linewidth source to resolve individual CO2-absorption lines, making distributed feedback laser diodes (DFB) ideal. However, they lack the necessary power levels for ranging over relevant distances, usually in the km-range. We therefore designed a fiber amplifier, based on an 11 m Er-/Yb-doped fiber, to boost the power level to about 1.3 W. The output was then expanded by a telescope and the back-scattered signal was collected by a second telescope, as schematically illustrated in Fig. 1 (a). The wavelengths could be tuned about 3 nm with a 35 dB signal-to-noise ratio, as shown in Fig. 1 (b), by adjusting the driving current to the DFB, while keeping a linewidth of about 3 MHz –well below the CO2-linewidth around 1 GHz at normal pressure. The system was used to measure the atmospheric CO2-concentration above the city of Lund, Sweden, over a 15 hour period. Using the backscattered data from 48 different wavelengths over the R14, R16 and R18 absorption peaks, the range-resolved concentration, illustrated in Fig. 1 (c) with a 500 m bin discretization, could be retrieved. The large increase in the error at the final concentration bin is related to the nonlinear range mapping onto the detector, i.e. fewer pixels for greater distances. Regardless, these results show that our simple fiber source already fulfills the necessary requirements for field application of CW-DIAL.
关键词： atmospheric CO2-concentration,DIAL,fiber amplifier,Scheimpflug configuration,CO2-monitoring
更新于2025-09-11 14:15:04
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[IEEE IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium - Valencia, Spain (2018.7.22-2018.7.27)] IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium - MCT Avalanche Photodiode Detector FOR Two-MICRON Active Remote Sensing Applications
摘要： Mercury Cadmium Telluride electron initiated avalanche photodiodes demonstrated a breakthrough in lidar active remote sensing technology. A lidar detection system, based on an array of these devices, was integrated and characterized for 2-μm applications. Characterization experiments were focused on evaluating the dark current, gain and responsivity variations with bias voltage. Quantum efficiency and input dynamic range including noise-equivalent-power and maximum detectable power, were calculated from these results. Operating the detection system using four pixels at 77.6 K, 12 V bias resulted in a current responsivity of 615.8 A/W and a voltage responsivity of 1.45 GV/W. Minimum detectable power of 14 pW was obtained, which is equivalent to 5.7 fW/Hz1/2 noise-equivalent-power, indicating an average noise-equivalent-power of 1.4 fW/Hz1/2 per pixel. Work is in progress to integrate and validate this detection system using a newly developed triple-pulse integrated path differential absorption lidar for simultaneous and independent atmospheric measurements of water vapor and carbon dioxide.
关键词： lidar,DIAL,MCT,IR detector,IPDA
更新于2025-09-10 09:29:36