Experimental Calibration of the Overlap Factor for the Pulsed Atmospheric Lidar by Employing a Collocated Scheimpflug Lidar

4D hyperspectral surface topography measurement system based on the Scheimpflug principle and hyperspectral imaging

A four-dimensional (4D) hyperspectral surface topography measurement (HSTM) system that can acquire uniform inelastic signals [three-dimensional (3D) spatial data] and reflection/fluorescence spectra of an object is proposed. The key components of the system are a light-sheet profilometer based on the Scheimpflug principle and a hyperspectral imager. Based on the mapping relationships among the image coordinate systems of the two imaging subsystems and the coordinate system of the real space, the spectral data can be assigned to the corresponding 3D point cloud, forming a 4D model. The spectral resolution is better than 4 nm. 700 nm, 546 nm, and 436 nm are selected as the three primary colors of red, green, and blue to restore the color. The 4D hyperspectral surface reconstruction experiments of philodendron and chlorophytum have shown the good performance of the proposed HSTM system and the great application potential for plant phenotype and growth analysis in agriculture.

Identification of fluorescent aerosol observed by a spectroscopic lidar over northwest China

Bioaerosols play a significant role in climate change and variation of ecological environment. To investigate characterization of atmospheric bioaerosols, we conducted lidar measurement for observing bioaerosols close to dust sources over northwest China in April, 2014. The developed lidar system can not only allowed us to measure the 32-channel fluorescent spectrum between 343 nm to 526 nm with a spectral resolution of 5.8 nm but also simultaneously detect polarisation measurements at 355 nm and 532 nm, as well as Raman scattering signals at 387 nm and 407 nm. According to the findings, the lidar system was able to pick up the robust fluorescence signal emitted by dust aerosols. Especially the polluted dust, the fluorescence efficiency could reach 0.17. In addition, the efficiency of single-band fluorescence typically rises as the wavelength goes up and the ratio of fluorescence efficiency of polluted dust, dust, air pollutant and background aerosols is about 4:3:8:2. Moreover, our results demonstrate that simultaneous measurements of depolarization at 532 nm and fluorescence could better distinguish fluorescent aerosols than those at 355 nm. This study enhances the ability of laser remote sensing for real-time detecting bioaerosol in the atmosphere.

Small lidar ratio of dust aerosol observed by Raman-polarization lidar near desert sources

Previous studies have shown that the lidar ratio has a significant influence on the retrieval of the aerosol extinction coefficient via the Fernald method, leading to a large uncertainty in the evaluation of dust radiative forcing. Here, we found that the lidar ratios of dust aerosol were only 18.16 ± 14.23sr, based on Raman-polarization lidar measurements in Dunhuang (94.6°E, 40.1°N) in April of 2022. These ratios are much smaller than other reported results (∼50 sr) for Asian dust. This finding is also confirmed by some previous results from lidar measurements under different conditions for dust aerosols. The particle depolarization ratio (PDR) at 532 nm and color ratio (CR, 1064 nm/532 nm) of dust aerosols are0.28 ± 0.013 and 0.5-0.6, respectively, indicating that extremely fine nonspherical particles exist. In addition, the dust extinction coefficients at 532 nm range from2 × 10^-4 to 6 × 10^-4m^-1for such small lidar ratio particles. Combining lidar measurements and model simulation by the T-matrix method, we further reveal that the reason for this phenomenon is mainly due to the relatively small effective radius and weak light absorption of dust particles. Our study provides a new insight into the wide variation in the lidar ratio for dust aerosols, which helps to better explain the impacts of dust aerosols on the climate and environment.

Vertical Structure of Dust Aerosols Observed by a Ground-Based Raman Lidar with Polarization Capabilities in the Center of the Taklimakan Desert

The vertical structure of dust properties in desert sources is crucial for evaluating their long-range transportation and radiative forcing. To investigate vertical profiles of dust optical properties in the Taklimakan Desert, we conducted ground-based polarization Raman lidar measurements in Tazhong (83.39°E, 38.58°N, 1103 m above sea level), located at the center of the Taklimakan Desert in the summer of 2019. The lidar system developed by Lanzhou University for continuous network observation is capable of measuring polarization at 532 and 355 nm and detecting Raman signals at 387, 407, and 607 nm. The results indicate that dust aerosols in the central Taklimakan Desert were regularly lifted over 6 km during the summer with a mass concentration of 400–1000 µg m−3, while the majority of the dust remained restricted within 2 km. Moreover, the height of the boundary layer can reach 5–6 km in the afternoon under the strong convention. Above 3 km, dust is composed of finer particles with an effective radius (Reff.) less than 3 μm and a Ångström exponent (AE) related to the extinction coefficient (AEE)532,355 greater than 4; below 3 km, however, dust is dominated by coarser particles. In addition, the particle depolarization ratios (PDR) of Taklimakan dust are 0.32 ± 0.06 at 532 nm and 0.27 ± 0.04 at 355 nm, while the lidar ratios (LRs) are 49 ± 19 sr at 532 nm and 43 ± 12 sr at 355 nm. This study firstly provides information on dust vertical structure and its optical properties in the center of the desert, which may aid in further evaluating their associated impacts on the climate and ecosystem.

Inelastic hyperspectral Scheimpflug lidar for microalgae classification and quantification

An inelastic hyperspectral Scheimpflug lidar system was developed for microalgae classification and quantification. The correction for the refraction at the air-glass-water interface was established, making our system suitable for aquatic environments. The fluorescence spectrum of microalgae was extracted by principal component analysis, and seven species of microalgae from different phyla have been classified. It was verified that when the cell density of Phaeocystis globosa was in the range of ${{1}}{{{0}}^4}\sim{{1}}{{{0}}^6}\;{\rm{cell}}\;{\rm{m}}{{\rm{L}}^{- 1}}$, the cell density had a linear relationship with the fluorescence intensity. The experimental results show our system can identify and quantify microalgae, with application prospects for microalgae monitoring in the field environment and early warning of red tides or algal blooms.