Shunxing Hu

Measurements of aerosol phase function and vertical backscattering coefficient using a charge-coupled device side-scatter lidar

By using a charge-coupled device (CCD) as the detector, side-scatter lidar has great potential applications in the near range atmospheric detection. A new inversion method is proposed for CCD side-scatter lidar (Clidar) to retrieve aerosol phase function and vertical backscattering coefficient. Case studies show the retrieved results from Clidar are in good agreements with those obtained from other instruments. It indicates that the new proposed inversion method is reliable and feasible and that the Clidar is practicable.

Retrieving aerosol backscattering coefficient for short range lidar using parameter selection at reference point

A new method is proposed based on the analysis of lidar equation which selects aerosol backscatter ratio at a reference point for short range lidar in data processing. Simulation computation and experimental comparison results show that this method is reasonable and feasible. The method is applied to short range lidars, such as atmospheric monitoring lidar-2 (AML-2) and micro-pulse lidar (MPL).

Cirrus cloud properties measurement using lidar in Beijing

Cirrus cloud has an important effect on the radiation balance between the earth’s surface and the atmosphere. The vertical structures, optical depth and effective lidar ratio of cirrus cloud detected by Mie scattering-polarization-Raman lidar system in Beijing from April 11 to December 31, 2012 are analyzed. The results show that the cloud height in Beijing is lower in spring and higher in autumn, with a mean value of about 8km. The mean of cloud thickness is 0.74km. The mean of optical depth is 0.092, and most observed cirrus cloud is thin while optical depth is less than 0.3. The effective lidar ratio of cirrus is lower in summer and higher in winter, inversely related to local temperature, with a mean value of 32.29Sr.

Optimization of band-pass filtering parameters of a Raman lidar detecting atmospheric water vapor

It is very important for daytime Raman lidar measurement of water vapor to determine the parameters of a band-pass filter, which are pertinent to the lidar signal to noise ratio (SNR). The simulated annealing (SA) algorithm method has an advantage in finding the extremum of a certain cost function. In this paper, the Raman spectrum of water vapor is simulated and then a first realization of a simulated annealing algorithm in the optimization of a band-pass filter of a Raman lidar system designed to detect daytime water vapor is presented. The simulated results indicate that the narrow band-pass filter has higher SNR than the wide filter does but there would be an increase in the temperature sensitivity of a narrowband Raman water vapor lidar in the upper troposphere. The numerical simulation indicates that the magnitude of the temperature dependent effect can reach 3.5% or more for narrow band-pass Raman water vapor measurements so it is necessary to consider a new water vapor Raman lidar equation that permits the temperature sensitivity of these equations to be confined to a single term.

Computational-weighted Fourier single-pixel imaging via binary illumination

Single-pixel imaging has the ability to generate images at nonvisible wavelengths and under low light conditions and thus has received increasing attention in recent years. Fourier single-pixel imaging (FSI) utilizes deterministic basis patterns for illumination to greatly improve the quality of image reconstruction. However, the original FSI based on grayscale Fourier basis illumination patterns is limited by the imaging speed as the digital micro-mirror devices (DMD) used to generate grayscale patterns operate at a low refresh rate. In this paper, a new approach is proposed to increase the imaging speed of DMD-based FSI without reducing the imaging spatial resolution. In this strategy, the grayscale Fourier basis patterns are split into a pair of grayscale patterns based on positive/negative pixel values, which are then decomposed into a cluster of binary basis patterns based on the principle of decimalization to binary. These binary patterns are used to illuminate the imaged object. The resulting detected light intensities multiply the corresponding weighted decomposed coefficients and are summed, and the results can be used to generate the Fourier spectrum for the imaged object. Finally, an inverse Fourier transform is applied to the Fourier spectrum to obtain the object image. The proposed technique is verified by a computational simulation and laboratory experiments. Both static and dynamic imaging experiments are carried out to demonstrate the proposed strategy. 128 × 128 pixels dynamic scenes at a speed of ~9 frames-per-second are captured under 22 KHz projection rate using a DMD. The reported technique accelerates the imaging speed for DMD-based FSI and provides an alternative approach to improve FSI efficiency.

Lidar studies of microphysical properties of cirrus clouds

Three microphysical backscatter ratios (color ratio, depolarization ratio, and lidar ratio) widely used for interpretation of lidar signals returned from cirrus clouds have been calculated for the first time. The physical-optics code developed earlier by the authors is applied. Though the data are obtained for the hexagonal ice plates and columns, that are the simplest crystal shapes, their arbitrary spatial orientation has been taken into account. The lidar experimental data measuring simultaneously the depolarization ratio and color ratio in cirrus clouds are also presented.

Fluorescence lidar for remote monitoring of plant

The laser-induced fluorescence (LIF) characteristic of plant is directly linked to the photosynthesis. The LIF lidar for remote monitoring of plant has been suggested as one of the useful tools to identify plant species and determine its physiological status for a long time. So recently a LIF lidar for remote sensing of plant in Anhui Institute of Optics and Fine Mechanics is developed. It transmits laser beam at wavelength of 354.7 and 532 nm, and receives elastic echo and fluorescence echo at wavelength of 680 and 740 nm. Numerical simulations are carried out to determine achievable lidar performance including operation range. Validity of fluorescence signal is certified and then some results are presented. Comparison of the fluorescence characteristic among birch, conifer, and algae show that the uorescence lidar is one of the potential tools to differentiate plant species.

Convenient method for calibrating system constant of scanning water vapor Raman lidar

Lower tropospheric water vapor measurements are performed at nighttime using the mobile atmosphere monitoring lidar-2 (AML-2) which is operated by the Anhui Institute of Optics and Fine Mechanics. In this lidar system, a 354.7-nm light from a Nd:YAG laser is used as stimulating source, whose Raman shifted center wavelengths are at 386.7 and 407.5 nm for nitrogen and water vapor, respectively. We present a novel and convenient method for determining the Raman lidar calibration constant according to the scanning performance of this lidar. We are likewise able to realize the measurement of water vapor profile in the low troposphere. The error induced by the uncertainty of calibrated constants is within 7% for the Raman lidar system. Experimental results from two months of study indicate that the method of calibrating the lidar system constant is feasible, and the Raman lidar performance is stable and reliable.