Remote sensing of atmospheric NO_2 by employing the continuous-wave differential absorption lidar technique

Abstract

Differential absorption lidar (DIAL) technique employed for remote sensing has been so far based on the sophisticated narrow-band pulsed laser sources, which require intensive maintenance during operation. In this work, a continuous-wave (CW) NO DIAL system based on the Scheimpflug principle has been developed by employing a compact high-power CW multimode 450 nm laser diode as the light source. Laser emissions at the on-line and off-line wavelengths of the NO absorption spectrum are implemented by tuning the injection current of the laser diode. Lidar signals are detected by a 45° tilted area CCD image sensor satisfying the Scheimpflug principle. Range-resolved NO concentrations on a near-horizontal path are obtained by the NO DIAL system in the range of 0.3-3 km and show good agreement with those measured by a conventional air pollution monitoring station. A detection sensitivity of ± 0.9 ppbv at 95% confidence level in the region of 0.3-1 km is achieved with 15-minute averaging and 700 m range resolution during hours of darkness, which allows accurate concentration measurement of ambient NO. The low-cost and robust DIAL system demonstrated in this work opens up many possibilities for field NO remote sensing applications.

Recent Advances in Aerosol and Trace Gas Monitoring by Employing the Scheimpflug Lidar Techniques

“…Atmospheric NO 2 has a relatively broadband absorption spectrum in the visible region around 450 nm, which provides the possibility of employing high-power multimode laser diodes for differential absorption measurements. Recently, we have developed a DIAL technique based on the Scheimpflug lidar, by introducing the tunable diode laser absorption spectroscopy (TDLAS) into the lidar fields [22]. The λ on wavelength at around 448.6 nm and the λ off wavelength at around 452.1 nm can be alternatively generated by modulating the driving current and tuning the case temperature of the high-power laser diode.…”

A Parameter-Free Calibration Process for a Scheimpflug Lidar for Volumetric Profiling

“…Briefly, the rule of Scheimpflug principles states that in a scenario where the object plane is tilted, sharp focus can be achieved by tilting the image sensor to a proper angle, where the image plane intersecting with the object plane and lens plane at the same point. Many scientific studies were benefit from it, such as particle image velocimetry [17][18][19], atmospheric aerosol monitoring [20][21][22][23][24][25][26] and fluorescence hyperspectral LIDAR [27][28][29][30]. Our previous study [31,32] has shown the potential to measure the distance profiles by light-sheet based two-dimensional Scheimpflug LIDAR, which also demonstrates the ability of large measuring range.…”

Preliminary Studies on Atmospheric Monitoring by Employing a Portable Unmanned Mie-Scattering Scheimpflug Lidar System

“…The Scheimpflug lidar technique has recently been developed for atmospheric aerosol monitoring, combustion diagnostics, etc. [30][31][32][33][34][35][36][37][38][39][40]. The range-resolved atmospheric backscattering signal can be retrieved by a Scheimpflug-principle based imaging system.…”