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The objective of this work was to investigate the effects of intrinsic fluorescence on the detection capability for biological aerosols of an UV fluorescence lidar with selected design parameters. Numerical simulations, based on the fluorescence lidar equation, were performed for fluorescence spectra ranging from 300 nm to 800 nm, where the fluorescence was induced by a pulsed laser at 266 nm. Simulation results show that the minimal detectable concentration of biological aerosols increases with detection range at different rates for different solar zenith angles, and that the uncertainties of the minimal detectable concentrations increase sharply with ranges. Lowest concentrations of biological aerosols are expected to be detectable during the night. In the day-time, aerosols emitting intrinsic fluorescence wavelengths are expected to be detectable at larger distances, with a relatively large uncertainty of the minimal detectable concentration. [ABSTRACT FROM AUTHOR]

Pollen is one of the important allergens in allergic diseases. The objective of this research effort is to investigate the use of a fluorescence lidar to measure concentrations of pollens in the atmosphere. The fluorescence lidar was constructed with a pulsed Nd:YAG laser, employing at fourth harmonic and second harmonic. A 250 mm diameter custom telescope was used to receive optical spectra from 260 nm–560 nm excited by 266 nm, and R7506 Photomultiplier tubes for two linear orthogonal polarization applications at 532 nm. Range-resolved fluorescence signals are collected in 32 channels of compound PMT sensor coupled with Czerny–Turner spectrograph. Based on the current configurations, we performed a series of simulations to estimate the measurement range and the concentration resolutions of pollens. With a relative error of less than 10%, theoretical analysis shows that the system is capable of identify a minimum concentration of pollen grains at 19 particles L −1 and 1 particles L −1 at daytime and nighttime within a range of 1.0 km, which is capable of identify a minimum concentration of pollen grains at 903 particles L −1 and 10 particles L −1 at daytime and nighttime within a range of 5.0 km. [ABSTRACT FROM AUTHOR]

The real aerosol size distributions were obtained by aerodynamic particle sizer spectrometer (APS) in China YinChuan. The lidar ratios at wavelengths of 355 nm, 532 nm and 1064 nm were calculated using Mie theory. The effective radius of aerosol particles r eff and volume C / F ratio (coarse/fine) V c/f were retrieved from the real aerosol size distributions. The relationship between multiwavelength lidar ratios and particle r eff and V c/f were investigated. The results indicate that the lidar ratio is positive correlated to the particle r eff and V c/f . The lidar ratio is more sensitive to the coarse particles. The short wavelength lidar ratio is more sensitive to the particle V c/f and the long wavelength lidar ratio is more sensitive to the particle r eff . The wavelength dependency indicated that the lidar ratios decrease with increasing the wavelength. The lidar ratios are almost irrelevant to the shape and total particles of aerosol size distributions. [ABSTRACT FROM AUTHOR]

• Raman spectra and Brillouin frequency shift can be combined for inversion of ocean salinity. • This paper proposes an inversion method of ocean salinity based on back propagation neural networks. • Compared with the physics-based algorithm model results, the salinity inversion accuracy of ocean salinity is improved. • This model can achieve high-speed and high-precision inversion of seawater salinity. To achieve high-precision and high-speed inversion of salinity using lidar data, this paper proposes a method for inversion of salinity based on back propagation neural network. Both the Raman spectra and the Brillouin frequency shift are related to temperature and salinity of ocean. However, pressure, refractive index, sound velocity, suspended particles, colored dissolved organic matter and ocean currents will affect the detection results when using lidar detection. Therefore, we establish a neural network model with 8 input parameters (NN-8), 5 input parameters (NN-5), and 2 input parameters (NN-2) and compares the inversion results of three models, NN-8 and NN-5 with higher accuracy, analyzes the correlation between the measurement results and the inversion results. The correlation coefficients of both NN-8 and NN-5 are greater than 0.999. Their RMSEs are 0.203‰ and 0.205‰, and REs are 0.09% and 0.105%, respectively. NN-5 can achieve higher inversion precision with fewer parameters. The influence of detection parameters on salinity inversion is evaluated using connection weights. Brillouin frequency shift and Raman spectra play a leading role in the salinity inversion, and other influencing factors can help to improve the inversion accuracy. Raman spectra at different salinities were detected experimentally, and the results are verified using the established model. The model results are consistent with the experimental results, and the error is less than 0.4‰. Compared with other classical regression methods, the results showed that the inversion results have high accuracy, and their errors are all less than 0.4‰. The research can offer data support for the global climates and ecosystems. [ABSTRACT FROM AUTHOR]

A fiber-optic spectroscopic rotational Raman lidar is demonstrated with the visible wavelength fiber Bragg grating technique for profiling the atmospheric temperature. Two-channel pure rotational Raman optical signals are extracted from lidar echo signals by two sets of visible wavelength fiber Bragg gratings. The rejection-type of fiber Bragg grating in visible region is successfully fabricated through the zero-order nulled phase mask. Its most significant parameter, out-of-band rejection, for fiber-optic spectroscopic system is tested to ensure the spectral purity of rotational Raman channel. A temperature profile up to a 0.7-km height is obtained by pure rotational Raman lidar with 300-mJ laser pulse energy, and a 250-mm telescope. Preliminary results of observations show that this fiber-optic spectroscopic scheme with high mechanical stability has >70-dB suppression to elastic backscattering in lidar echo signals. [ABSTRACT FROM AUTHOR]

Fringe-imaging Fabry–Perot interferometer (FIFPI) and fringe-imaging Mach–Zehnder interferometer (FIMZI) used as frequency discriminator for incoherent molecular Doppler lidar were analyzed, respectively. For a pure molecular backscattered signal, performances (wind measurement sensitivity and signal-to-noise ratio) of both FIFPI and FIMZI systems were simulated based on the U.S. standard atmospheric model. Comparisons of two systems were made under the same emitting and receiving parameters with certain wind speed dynamic range. Simulated results show that, though relatively lower sensitivity to Doppler shift, the single-channel FIMZI system provides a factor of 1.3 times smaller error in the horizontal wind velocity than that of FIFPI at a range of 20 km. We expect that the FIMZI frequency discriminator would provide an effective technique to improve the measurement accuracy for incoherent molecular Doppler lidar. [ABSTRACT FROM AUTHOR]

Abstract: According to the characteristics of a Lidar echo signal contaminated by noise, especially in strong background light, an effective de-noising method of wavelets based on a soft threshold is proposed to reduce the Lidar echo signal noise and improve the signal to noise ratio of system. The principles and methods of wavelet transforms and wavelet de-noising are utilized to de-noise the noisy signals. Some preliminary simulations are carried out to reduce the noise of the simulated signals in order to verify the feasibility of the de-noising method. In addition, using experimental data of the Lidar echo signals contaminated by noise in the strong background light, the de-noising range-square-corrected signals and the retrieved aerosol extinction coefficient are obtained. The results show evidence of the de-noising effects and demonstrate that this method can effectively de-noise the noisy Lidar signals in strong background light and achieve improvement in the signal to noise ratio of system. [Copyright &y& Elsevier]

Abstract: An eye-safe micro-pulsed Mie scattering lidar (MPL) system at a wavelength of 532nm was built for routine observations of atmospheric optical properties of the lower troposphere. The lidar is operated in an analog mode with three-dimensional (3D) scanning capability. Observations were carried out for obtaining detailed information of the urban boundary layer (UBL) over Xi''an, China. The parameters that can be measured include aerosol extinction coefficient and optical depth (AOD), structure of the UBL, and the mixed layer depth (MLD). The results indicate that the height of UBL shows both temporal and spatial variations over Xi''an. It is generally lower in the early morning and dusk than during the daytime. MLD is driven by the convective air motions and strongly correlated with the aerosol diurnal changes which tend to fall during night and rise during day. [Copyright &y& Elsevier]

Abstract: The Fabry–Perot Etalon (FPE) is widely used in Doppler wind lidar as frequency discriminator and its performance is certainly affected by the propagation properties of Gaussian beam. The divergence angle of lidar returns affected by the quality factor M 2 and magnification of beam expander (MBE) of outgoing laser is firstly discussed. Also, the corresponding sensitivity of system on wind velocity is analyzed. The numerical results show that the divergence angle of lidar returns and FPE transmission varied with height, the resulting sensitivity of system is decreased and the wind velocity error is relatively steady in the far field. Consequently, for the wind lidar using FPE as frequency discriminator, it is supposed that the outgoing laser with both lower beam quality factor M 2 and higher MBE are requested, in particularly, the system calibration due to FPE instability must be considered in the near field. [Copyright &y& Elsevier]

Abstract: A new spectroscopic filter constructed with a high-spectral-resolution grating and two narrow-band mirrors is designed to separate the elastic scattering and the vibrational Raman scattering spectra in an ultraviolet (UV) Raman lidar system. The density of humidity and water vapor mixing ratio are calculated from the vibrational Raman scattering signals of N2 and H2O. Water vapor mixing ratio is retrieved from this development. With this measured water vapor mixing ratio, the relative humidity is calculated with atmospheric temperature profile obtained by another Raman temperature lidar. Preliminary experiments and comparison results between lidar and radiosonde showed that the UV Raman lidar system has the capability for profiling the water vapor mixing ratio up to a height of 2km with less than 10% of the uncertainty under the conditions of laser energy of 300mJ and signal-averaging time of 10min. [ABSTRACT FROM AUTHOR]

Abstract: In consideration of the complexity and the high cost of the dual CCD intersection vertical target when it is used indoor. A novel measuring principle of one linear array CCD camera vertical target is presented. One low-power semiconductor sector-like laser with projection board is used to be the lamp-house of the CCD camera. The detection light screen of the CCD camera and the laser lamp-house are adjusted to same plane. When the projectile through the detection light screen, it blocks the part light of the laser and leaves a shadow of projectile on the board. The shadow and its coordinate are acquired and calculated by the CCD camera and computer, and the projectile coordinate of X and Y can be gotten through image processing and further calculation. The measuring principle and the formulas are given, and the measuring error is analyzed. The result indicates that the coordinate error of X and Y less than 1.5 and 2.2mm, respectively, when the detection light screens is 1m×1m, The principle presented has the advantages that measurement principle is simple, low cost and easy engineering. [Copyright &y& Elsevier]

• The influence factors on the detection accuracy of atmospheric water vapor using a solar-blind ultraviolet Raman lidar are analyzed, including the O 3 , NO 2 and SO 2 absorptions, fluorescence interference, the solar background noise, optical cross talks in the polychromator system and so on. • Deviations and the relative errors of water vapor retrieval due to all the predicted influencing factors are accurately estimated. • To enhance the detection accuracy of the water vapor mixing ratio, the real-time measurement of O 3 concentration with height is required especially in Xi'an, which can be succeeded by adding one channel to detect the vibrational Raman signal of O 2 in the solar-blind ultraviolet Raman lidar. • The rejection rate with more than 5 orders of magnitude to elastic scattering signal is required in the design of high resolution polychromator to avoid the optical cross talk between each extracted spectrum. Solar-blind ultraviolet Raman lidar can realize the daytime detection of atmospheric water vapor, as the transmitting wavelength of 266.0 nm and its excited vibrational Raman spectra of N 2 , O 2 and H 2 O are within the solar-blind region. However, the spectra of the O 3 , NO 2 , SO 2 absorptions and fluorescence are within the solar-blind region as well, and Raman channel of H 2 O still has a small amount of residual solar background noise, which will influence the detection accuracy and detection capability of the solar-blind ultraviolet Raman lidar. Moreover, although a high efficiency polychromator is required to extract the vibrational Raman spectra of N 2 , O 2 and H 2 O, the suppression of aerosol Mie scattering and molecular Rayleigh scattering, and optical cross-talks are still required to discuss carefully in detail. Simulation results show that the retrieval accuracy of water vapor mixing ratio using the solar-blind Raman lidar are mainly influenced by the O 3 absorption and the optical cross-talk of aerosol Mie scattering and molecular Rayleigh scattering. The rejection ratio with more than 5 orders of magnitude to elastic scattering signal is required in the design of polychromator to avoid the optical cross-talk between each extracted spectrum. The influences of NO 2 , SO 2 absorptions, solar background noise and fluorescence on the retrieval of water vapor mixing ratio can be neglected. The theoretical analysis of the solar-blind ultraviolet Raman lidar on the retrieval of water vapor mixing ratio can further enhance the performance of the system detection accuracy and detection capability. [ABSTRACT FROM AUTHOR]

• Time-resolved CFI image acquired. • The fast rise section and the slow decrease section of the ChlF kinetics curve were measured. • Characteristics were extracted and a ANN model was established. The objective of this study was to check whether different water and nitrogen treatments and, even the water-nitrogen coupling effect of plants could be correctly differentiated via chlorophyll a fluorescence image. We developed a classification method using the imaging analysis of chlorophyll a fluorescence induction based on Artificial Neural Network. The measurements were carried out on scheffera octophylla (Lour.) Harms , and the images were recorded at 690 nm with a high-resolution imaging device consisting of LEDs for an excitation at 460 nm and an Electron-Multiplying CCD camera. The effect of three different water and three different nitrogen treatments on the fluorescence parameters were obtained by hundreds of time-resolved fluorescence images. We used a Radial Basis Function neural network to model and test the sample data. The results showed that the different water and nitrogen statuses of plants were identified by the chlorophyll a fluorescence images and showed a high recognition accuracy. Compared with nitrogen, water had more of an influence on chlorophyll a fluorescence and was easier to identify. However, because the water and nitrogen restrict and promote each other, studying the coupling effect of water and nitrogen is necessary. Nine levels of water-nitrogen coupling plants were tested and classified. We discovered that a significant decrease on the classified accuracy was observed for the high nitrogen and low nitrogen treatments, while under a medium N-supply, the recognition rate was high. The method in this paper allowed plants to be classified under different water and nitrogen treatments, and has the potential to monitor the water and nitrogen coupling effect of plants in situ. [ABSTRACT FROM AUTHOR]

• A generalized theoretical model (GTM), suitable for various imaging-based atmospheric lidar techniques, has been concepted and established. • The dependencies of the range resolution, the blind range, etc. on optical configurations have been revealed based on the GTM and simulation studies. • A number of factors, providing significant guidance for quantitative system designment, have been proposed and simulated. In recent years, imaging-based lidar techniques have been widely studied and employed in atmospheric remote sensing, while different theoretical descriptions are introduced for lidar systems with specific optical configurations and a universal guideline for optimizing system performance is still lacking. In this work, a generalized theoretical model (GTM), suitable for various imaging-based atmospheric lidar techniques, has been concepted and established for describing the relationship between the system performances and optical configurations, where a few factors have been derived and defined. Comprehensive simulation studies based on the GTM have demonstrated that the range resolution, the blind range, the minimum scattering angle of the lidar signal and the tilt angle of the image sensor are strongly dependent on the focal length of the receiving lens (or telescope) and the transmitter–receiver separation, etc. In particular, the range resolution is proportional to the product between the focal length and the separation. Besides, the intensity factor, the signal-to-background ratio (SBR) factor, as well as the signal-to-noise ratio (SNR) factor, which are immune from atmospheric conditions, etc., have been proposed and deduced to quantify the performances of imaging-based lidar system with different optical configurations. It has been found out that the SBR factor, an indicator for the requirement on the dynamic range of the image sensor, is inversely proportional to the separation. Meanwhile, the intensity factor and the SNR factor are related to the separation, the focal length as well as the aperture of the receiving lens, etc. The GTM provides valuable insight for understanding the principle of the imaging-based atmospheric lidar technique as well as a general guideline for system design and implementation. [ABSTRACT FROM AUTHOR]

Abstract: The modified super-wide-angle Sagnac imaging interferometer (MSASII) based on liquid crystals on silicon (LCoS) is proposed as a novel device for the detection of the upper atmospheric wind field. This device employs the phase-only modulation (POM) of LCoS coupled with the MSASII, and can measure phase changes in multi-band emissions without moving mirror. It can be used to replace the conventional Michelson’s interferometer with step-moving mirror device. The optical path difference (OPD) equation of MSASII-LCoS is derived, and the four compensation conditions (field, chromatics, thermal and achromaticity of thermal compensations) are discussed within the scope of wind measurement. The real parameters of LCoS and optical glasses are selected for numerical simulation and analysis. Three aurora lines (732.0, 630.0 and 557.7nm) are considered, and their phase variations are 3.61, 2.02 and 0.15 fringes at the same incident angle of 3°, respectively. The rate of change of OPD with temperature is the magnitude of 10−6 cm/K, and the corresponding phase variations are within 0.09 fringes. The accuracy of phase modulation can be 0.614×10−2 rad when LCoS of 10-bits is used. The novel model MSASII-LCoS shows its advantage for atmospheric wind measurement in the aspects of the overall structure, anti-vibration, operational flexibility and detection accuracy. [ABSTRACT FROM AUTHOR]

Na 0.5 Bi 0.5 TiO 3 -based solid solutions are one of the most promising lead-free piezoelectric candidates since they can be easily tailored to exhibit large electrostrain. However, the large hysteresis and temperature-dependence of the electrostrain response are longstanding obstacles for their practical applications. In the present study, 0–3 type composites were developed with 0.97(0.94Na 0.5 Bi 0.5 TiO 3 -0.06BaTiO 3)-0.03AgNbO 3 (NBT-6BT-3AN) matrix phase and ZnO inclusions. The optimum addition of 5 wt.% ZnO in the composites leads to reduction in hysteresis of electrostrain by 35% in comparison with pure NBT-6BT-3AN at room temperature. Meanwhile, electrostrain of the composites maintains superior temperature stability, with a variance of less than ±10% in the temperature range between 25 and 125 °C. The reason for the improvement of electrostrain is proposed to be attributed to the ergodic/nonergodic mixture phases induced by residual stress between the inclusion and matrix, as well as the phase evolution caused by the incorporation of Zn2+ into the matrix. Therefore, this work provides a new strategy to improve the electromechanical properties of Na 0.5 Bi 0.5 TiO 3 -based ceramics. [ABSTRACT FROM AUTHOR]

• To study the advantages and disadvantages of the single-longitudinal-mode (SLM) high-spectral-resolution lidar (HSRL) and multi-longitudinal-mode (MLM) HSRL using the Mach-Zehnder interferometer (MZI) as the spectral discriminator for measuring aerosol optical properties, the working principle, optimal OPD setting, and the detection performance are comparative discussed in the SLM HSRL and MLM HSRL, respectively. • To evaluate the performances of SLM HSRL and MLM HSRL, we simulate and analyze the variation of the effective transmittance of MZI and the spectral discrimination ratio (SDR) with different optical path differences (OPD) of MZI, frequency differences, and divergence angles, respectively. The simulation results show that the optimal OPDs of MZI should be set at 165 mm and 1000 mm in the SLM HSRL and MLM HSRL, respectively. The spectral separation degree of the SLM HSRL is better than the MLM HSRL. The MLM HSRL has higher requirements for the environmental parameters and the echo beam collimation than the SLM HSRL. • The preliminary experimental observation of aerosol optical properties is carried out in Xi'an based on the constructed SLM HSRL and MLM HSRL with the tunable MZI. The preliminary experimental results show that, compared with the MLM HSRL, the difference between the range square corrected signal (RSCS) of Rayleigh channel and the RSCS of Mie channel for the SLM HSRL is larger than, which proves that the SLM HSRL has a preferably separation for aerosol Mie scattering signals and molecular Rayleigh scattering signals. Besides, the detection range of the SLM HSRL is lower than that of the MLM HSRL under the same control voltage and the optimal OPD of MZI (165 mm and 1000 mm) conditions. High-spectral-resolution lidar (HSRL) is a powerful tool for aerosol measurements. With/without laser seeding technique in the transmitted laser, the HSRL can be distinguished as the single-longitudinal-mode (SLM) HSRL or the multi-longitudinal-mode (MLM) HSRL, and the Mach-Zehnder interferometer (MZI) with periodic transmittance function can be used as the spectral discriminator in both the SLM HSRL and MLM HSRL. To in-depth knowledge of the respective advantages of the SLM HSRL and MLM HSRL for measuring aerosol optical properties, the working principle, optimal parameter setting, and detection performance of the SLM HSRL and MLM HSRL are analyzed and discussed in detail, respectively. The working principle of the SLM HSRL and MLM HSRL indicate that the effective transmittance of MZI is the important parameter of data retrieval, the main source of retrieval uncertainties, and the key factor of MZI optical path difference (OPD) settings. To ensure that the MZI can achieve the preferable separation for aerosol Mie scattering signals and molecular Rayleigh scattering signals, the optimal OPDs of MZI are set at 165 mm and 1000 mm in the SLM HSRL and MLM HSRL from the aspects of the effective transmittance of MZI and the spectral discrimination ratio (SDR). Besides, to analyze the influence of frequency difference and divergence angle for the detection performance of HSRL, the effective transmittance of MZI and SDR are simulated and the results show that the MLM HSRL has higher requirements for the environmental parameters and the echo beam collimation than the SLM HSRL. Moreover, the HSRLs with SLM and MLM transmitted lasers are constructed in Xi'an for measuring aerosol optical properties. The preliminary measurement results show that the range square corrected signal (RSCS) of Rayleigh channel is smaller than that of Mie channel in both the SLM HSRL and MLM HSRL, while the difference between RSCS of Rayleigh channel and RSCS of Mie channel in the SLM HSRL is larger than that in the MLM HSRL, and the detection range of the SLM HSRL is lower than that of the MLM HSRL. [ABSTRACT FROM AUTHOR]

• A fiber Mach-Zehnder interferometer based incoherent Doppler lidar system for vertical wind profiling is established. • FMZI Doppler lidar is designed to be sensitive to Mie backscattering signals but insensitive to Rayleigh backscattering signals. • The reference signal is used for calibrating the laser-frequency jitter. • Vertical wind profiles up to a height of approximately 550 m were obtained with a 24 m vertical spatial resolution by the FMZI Doppler lidar in Xi'an (China) on April 17, 2018. An incoherent Doppler lidar system based on a fiber Mach-Zehnder interferometer (FMZI) for vertical wind profiling is established. The FMZI Doppler lidar is sensitive to Mie backscattering signals but insensitive to Rayleigh backscattering signals and has a 9.99 cm FMZI arm-length difference. The lidar operates with an injection-seeded Nd:YAG laser at 532 nm and a 406-mm-aperture telescope. Vertical wind profiles up to a height of approximately 550 m were obtained with a 24 m vertical spatial resolution by the FMZI Doppler lidar in Xi'an (China) on April 17, 2018. The reference signal is used for calibrating the laser-frequency jitter. The measured vertical wind velocities are in good agreement with the coherent Doppler lidar vertical wind measurements made simultaneously from the same location. The FMZI Doppler lidar realized the critical step on the road to practice. [ABSTRACT FROM AUTHOR]

• The spectra of laser echo signals of the UV multi-longitudinal-mode high-spectral-resolution lidararebroadened to 35 GHz, which should be taken as the quasi-monochromatic rather than the monochromatic. • The effective transmittance of Mach–Zehnder interferometer is a function of the complex degree of coherenceunder the condition of quasi-monochromatic light. • The phase of the complex degree of coherence for both UV MLM laser and its corresponding Mie–Rayleigh backscattering signals is zero, while their modulus of the complex degree of coherence are optimal when the optical path difference of Mach–Zehnder interferometer equals two times of laser optical cavity length. • The optimal modulus of the complex degree of coherence for the laser echo signals is a function of the backscatter ratio and affects the effective transmittance for both mie and rayleigh channels of Mach–Zehnder interferometer. • The retrieval of aerosol backscattering coefficientusing the MLM HSRLis deduced using the parameter of the complex degree of coherence, and the retrieval uncertainties are analyzed from the points of systematic effect and random effect. The effective transmittance of Mach–Zehnder interferometer is a function of the complex degree of coherence in the construction of the UV multi-longitudinal-mode (MLM) high-spectral-resolution lidar (HSRL), in which the spectra of laser echo signals are broadened to 35 GHz and should be recognized as the quasi-monochromatic rather than the monochromatic. In this paper, we calculate the complex degree of coherence of the Mach–Zehnder interferometer (MZI) for the UV MLM laser and its corresponding Mie–Rayleigh backscattering signals. The results show that the phase of the complex degree of coherence for both quasi-monochromatic lights is zero, while their modulus of the complex degree of coherence are optimal when the optical path difference of MZI equals two times of laser optical cavity length. For the specified UV MLM laser with the linewidth of each longitudinal mode of 100 MHz, mode number of 80 and mode interval of 375 MHz within laser linewidth of 30 GHz, the optimal modulus of the complex degree of coherence has a fixed value of 0.776, while the optimal modulus of the complex degree of coherence for the laser echo signals is a function of the backscatter ratio and affects the effective transmittance for both Mie and Rayleigh channels of MZI, which are verified using the atmospheric modeling. Moreover, the relative standard uncertainties of the retrieved aerosol backscattering coefficient using the MLM HSRL are analyzed considering the systematic effect and random effect. The simulation results show that the presence of aerosol layers deteriorate the accuracy of the retrieved aerosol backscattering coefficient sharply, and the relative standard uncertainty produced by the modulus of the complex degree of coherence of Mie scattering spectra can be realized to less than 4% by improving the stability of the MLM laser. [ABSTRACT FROM AUTHOR]

• A set of speckle image matching algorithms that add intensity model is proposed. • Linear least squares estimation is used for integer pixel matching algorithm. • Sub-pixel matching algorithm is derived combined IC-GN with intensity model. • It is suitable for illumination variation and can improve measurement accuracy. Digital image correlation is used to measure deformation and shape. In some complex scenes, the illumination of the measured surface may vary unevenly before and after deformation. The intensity change model is added to correlation function and a family of speckle image matching algorithms is obtained. In integer pixel matching, linear least square estimation is used to calculate the initial values of the intensity coefficients and integer pixel position; in subpixel matching, cyclic variable method is proposed to make the iteration converge. Compared with the current mainstream algorithm, the proposed method makes the physical meaning of correlation matching clearer, so that the correlation function can be defined according to the actual lighting environment, and correlation matching can be more accurate. The experimental results indicate that the proposed matching algorithm is suitable for applications where ambient light is constantly changing. [ABSTRACT FROM AUTHOR]

To obtain representative models of aerosol size distributions in the vertical dimension, we performed an extensive investigation on aerosol number concentration distributions from 0.1 µm to 3.0 µm based on airborne aerosol measurements, which were measured by a PCASP-100X on 33 flights over Northern China. A multi-modal lognormal size distribution with a base 10 logarithm is applied to fit the measured aerosol size distributions at different altitudes. Most of them can be fitted well by using a tri-modal distribution, while some of the data need to be fitted using a four-mode distribution. As the height increases, the aerosol distributions gradually become monotonous and display double-peak or single-peak lognormal distributions. Vertical variations in aerosol distributions over four days were analyzed and compared to each other. Statistical parameters of aerosol size distributions in the vertical dimension were obtained and analyzed. Relatively stable modal parameters from the ground to a height of 7 km were found for modes 1 and 2. The first and second peaks in the aerosol distributions were found from 0.08 µm to 1.2 µm and from 0.12 µm to 0.4 µm, and their medians were approximately 0.1 µm and 0.3 µm. The standard deviation did not change very much, from 0.05 µm to 0.6 µm and from 0.2 µm to 0.6 µm. The mean particle sizes in modes 1 and 2 were similar and showed an exponential decline with increasing height. Typical modal distributions of aerosol concentrations ranging in size from 0.1 µm to 3.0 µm over the vertical dimension in Northern China are presented along with statistical data. The parameterized formula is also provided in this paper. [ABSTRACT FROM AUTHOR]

From August to October 2010 lidar measurements of aerosols in the troposphere were performed at Otlica observatory, Slovenia, using a vertical scanning elastic lidar. The lidar data sample, which contains 38 nighttime vertical profiles of the mean aerosol extinction, was combined with continuous ozone concentration (O 3 ), particulate matter concentrations (PM) and daily radiosonde data. The obtained radiosonde- and lidar-derived heights of the atmospheric boundary layer (ABL), which varied considerably from day to day, were found to be in good agreement. The mean values of the aerosol optical depth (AOD) at 355 nm, were calculated separately for the ABL and for the free troposphere (FT). A ten-fold increase of the FT AOD was observed during the days with predicted presence of Saharan dust above the lidar site. To correlate AOD values with the type and origin of aerosols, backward trajectories of air-masses above Otlica were modeled using the HYSPLIT model and clustered. High ABL AOD values were found to be correlated with local circulations and slowly approaching air masses from the Balkans and low values with northwestern flows. The highest values correlated with southwestern flows originating in northern Africa. [ABSTRACT FROM AUTHOR]

• Obtaining soil reflectance spectral data with a spectral photometer. • Acquiring a series of alternative bands by correlation analysis. • Extracting characteristic bands of SOM, TN, AK and AP by weight analysis based on AHP. • Revising AHP judgment matrix with PSO algorithm for optimization. • BPNN inversion models outperform SVM and PLS in predicting TN, SOM, AP, and AK. The selection of characteristic bands of soil nutrients is crucial for the prediction of soil nutrient contents. In this paper, a measurement method based on the analytic hierarchy process (AHP) and reflectance spectrum is proposed to realize the extraction of characteristic bands and the prediction of soil nutrients. Firstly, a series of alternative bands are obtained by mathematical transformations and correlation analysis from the reflectance spectral curves of 30 soil samples. Then, to objectively reflect different dependencies of spectral bands on the soil nutrients, AHP is adopted for weight analysis, and the particle swarm optimization algorithm (PSO) algorithm is used to correct the expert scoring matrix. Via the weight allocation, weight normalization and weight threshold, the alternative bands meeting the sum threshold of weights > 0.5 are finally selected as the characteristic bands of soil nutrients, which are at 484 nm, 512 nm, and 760 nm for total nitrogen (TN), and at 384 nm, 736 nm, and 748 nm for available phosphorus (AP). Finally, three inversion models established by the characteristic bands are used to predict soil nutrient contents, which demonstrated the feasibility of the analytic hierarchy process for the extraction of characteristic bands and the prediction of soil nutrients. [ABSTRACT FROM AUTHOR]

In this work, an 808-nm Scheimpflug lidar (SLidar) system, employing a laser diode as the light source and an image sensor as the detector, has been utilized for practical applications of air pollution monitoring in urban area. A comprehensive retrieval method has been proposed and developed for reliable and automatic retrieval of the aerosol extinction coefficient (AEC) from near-horizontal scanning SLidar measurements. The characteristics of the pixel-intensity curves measured by the SLidar system have been statistically examined, and a quality control process is developed to eliminate abnormal lidar profiles. An improved Douglas-Pucker algorithm has been utilized for the determination of the boundary value of the AEC. The AEC profile is thus obtained according to the Klett method with the boundary value as the input. Meanwhile, an angular iterative retrieval (AIR) algorithm has been developed with the AECs at neighboring scanning angles as references, which is able to significantly improve the retrieval reliability of the AEC for each scanning angle. Comparison studies with a local pollution monitoring station have also been carried out to verify the present retrieval method. Besides, the Scheimpflug lidar technique in combination with the retrieval method has shown promising performance in tracking pollution sources in urban area. • A comprehensive retrieval method is developed to reliably obtain the aerosol extinction coefficient in air pollution monitoring with the Scheimpflug lidar. • An angular iterative retrieval (AIR) algorithm is proposed to overcome the issues of intensity fluctuation and atmospheric heterogeneity. • The Scheimpflug lidar in combination with the retrieval method has shown promising performance in tracking pollution sources. [ABSTRACT FROM AUTHOR]

In this study, a multi-wavelength polarization lidar was developed at the Lidar Center for Atmosphere Remote Sensing, in Xi’an, China to study the vertical distribution of the optical and microphysical properties of smog aerosols. To better understand smog, two events with different haze conditions observed in January 2015 were analyzed in detail. Using these data, we performed a vertical characterization of smog evolution using the lidar range-squared-corrected signal and the aerosol depolarization ratio. Using inversion with regularization, we retrieved the vertical distribution of aerosol microphysical properties, including volume size distribution, volume concentration, number concentration and effective radius. We also used the Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) model to analyze aerosol sources during the two episodes. Our results show that the most polluted area in the lower troposphere during smog episodes is located below a height of 1 km above the ground level; under more severe smog conditions, it can be below 0.5 km. In the case of severe smog, we found a large number of spherical and fine particles concentrated in the very low troposphere, even below 0.5 km. Surprisingly, a dust layer with a slight depolarization ratio was observed above the smog layer. [ABSTRACT FROM AUTHOR]

• Effective transmittance of MZI is a key parameter in the retrieval of aerosol characteristics using the MLM HSRL technique. • Effective transmittance of MZI is investigated using theoretical analysis, optical simulation and experimental measurement. • Retrieval uncertainty of aerosol backscattering coefficient is estimated using the complex degree of coherence of MZI. Effective transmittance is an important parameter of Mach-Zehnder interferometer in the retrieval of aerosol optical properties using the multi-longitudinal-mode high-spectral-resolution lidar, which is a function of the complex degree of coherence. In this paper, we retrieve the parameter of the complex degree of coherence for the multi-longitudinal-mode laser from the theoretical analysis, optical simulation and experimental measurements, which are 0.726, 0.678 and 0.453 using the Mach-Zehnder interferometer with the optimal optical path difference of two times of laser optical cavity length (∼1000 mm) and under the light illumination of the high power Nd:YAG laser with the mode number of 101 and mode interval of 300 MHz under the condition of laser linewidth of 1 cm−1 (30 GHz). The preliminary measurement results of aerosol optical properties using the constructing multi-longitudinal-mode high-spectral-resolution lidar show that the difference of the complex degree of coherence retrieved from the presented methods results in the relative error of 40% in the aerosol backscattering coefficient with thin cloud layer and 90% with the presence of dense aerosol layer. [ABSTRACT FROM AUTHOR]

[Display omitted] • A scalable, low-cost and green liquid-phase exfoliation method is used to fabricate the ReS 2 @Ti 3 C 2 photodetector. • The ReS 2 @Ti 3 C 2 photodetector shows sensitive high photoresponsivity about 59.6 μA/W. • The ReS 2 @Ti 3 C 2 photodetector exhibits excellent flexibility and folding resistance. • The improved photodetection of ReS 2 @Ti 3 C 2 is due to efficient charge transportation. Metal doping is a proven strategy to improve the performance of two dimensional (2D) optoelectronic devices in recent studies. Due to the high price and scarcity of the noble metal, low-cost and high-efficiency noble-metal-alternative as Ti 3 C 2 MXene is greatly anticipated. Herein, the ReS 2 @Ti 3 C 2 based photodetector is fabricated by liquid-phase exfoliation technique combined with electrophoretic deposited method. The ReS 2 @Ti 3 C 2 photodetector exhibits a high photocurrent density approximately 5.98 μA/cm2, wide detection ability in UV–vis region, and outstanding flexibility and folding resistance. The main reasons for the improved photodetection performance in ReS 2 @Ti 3 C 2 composites are the superior electron conductivity and the metallic properties of Ti 3 C 2 and strong charge transportation at the heterostructure interface. This work offers an effective way to improve the performance of 2D flexible optoelectronic devices by doping non-noble metallic conductors. [ABSTRACT FROM AUTHOR]

• We built a multi-angle polarization measurement system for a single particle to measure the scattering characteristics of aerosols. • We present a retrieval method to simultaneously estimate the aerosol complex refractive indices (ACRI) and particle size distribution (PSD) of aerosols based on the measured polarization scattering signals. • The proposed retrieval method benefits the research of climate modeling and atmospheric monitoring. Changes of polarization state in aerosol scattering processes are sensitive to various microphysical properties of particles, such as size distribution and complex refractive index. In this work, we present a method to estimate the complex refractive indices (ACRI) and particle size distribution (PSD) of aerosols based on the measured polarization scattering signals using our multi-angle Stokes vector analysis system of individual particles. Then we use the probability density function (PDF) of aerosols to weight the Stokes vector and compare it with Mie scattering theory to iteratively retrieve the optimal ACRI and PSD. The experimental results of six kinds of aerosol samples support the validity and feasibility of our method, implying the important potential of polarization scattering information extraction applied in dynamic monitoring, quantitative retrieval and fine identification of aerosols. [ABSTRACT FROM AUTHOR]

• Parameterized equations of PM mass concentration and extinction coefficient were established at different levels of relative humidity. • The sample datasets contain a large number of and long-term different seasonal and weather pollution conditions. • Derivation of PM mass concentration profiles by using single-wavelength Raman lidar and the parameterized equations. • Vertical distribution characteristics of PM 1 , PM 2.5 and PM 10 mass concentrations in Xi'an were obtained. Considering the importance of the aerosol optical parameters detection for environmental monitoring, a method of converting single-wavelength Raman lidar backscattered echoes to aerosol mass concentrations is proposed to obtain a high-resolution vertical distribution of particulate matter (PM) mass concentrations. PM x (x = 1, 2.5, 10) mass concentrations and extinction coefficients at 355 nm and 532 nm were obtained using a combination of a colocated visibility meter and wide-range particle spectrometer (WRAS), and parameterized equations between the aerosol extinction coefficient and mass concentration at different levels of relative humidity (RH) were established (the sample datasets included different seasonal and weather pollution conditions in Xi'an, China, for 2018 and 2019). The results demonstrate that parametric analysis of sample datasets at three levels of RH (RH < 60%, 60% ≤ RH < 75%, and RH ≥ 75%) can better reflect the long-term variation characteristics of aerosols: the aerosol extinction coefficients show an exponential relationship with PM 1 and PM 2.5 mass concentrations, and the correlation coefficients are both above 0.965 even at different levels of RH, while the correlation with PM 10 is 0.808. The extinction coefficient and RH profiles can be retrieved using single-wavelength Raman lidar, and then the aerosol mass concentration distribution can be calculated by combining parameterized equations. The deviation of mass concentration profiles between 355 and 532 nm Raman lidar was analyzed, and it is a constraint that the calculation of the PM mass concentration profile is made in the planetary boundary layer (PBL). The derivation uncertainty of PM x and the limitations of the method are also discussed. Finally, cases of vertical distribution and variations in PM x on pollution-free and hazy days are presented. [ABSTRACT FROM AUTHOR]

• Thegeneralretrievalequationsof aerosol optical properties using high-spectral-resolution lidarare deduced, which shows the effective transmittance of optical discriminator is the most important parameter in data retrieval. • A novel retrieval algorithm of aerosol optical properties using the multi-longitudinal-mode pulsed high-spectral-resolution lidar is presented, which is a function of complex coherence degreeand verified the correctness. • The absolute errors of the measurements of aerosol backscattering coefficient and optical depthusing the multi-longitudinal-mode high-spectral-resolution lidarare analyzed from the systematic effect and random effect, which shows that the absoluteerror of aerosol optical backscattering coefficient can be ignored and the absolute error of optical depth can be controlled within 0.4 in the majority of the lidar data when the relative error of δ is within 20%. • Thepreliminary experiments of the constructed multi-longitudinal-mode high-spectral-resolutionlidar areperformed.The retrieved results of aerosoloptical properties using the multi-longitudinal-mode high-spectral-resolutionlidarhas proven that the multi-longitudinal-mode high-spectral-resolutionlidarhasthe capability in the fine detection of aerosol optical properties. Multi-longitudinal-mode (MLM) high-spectral-resolution lidar (HSRL) selects an optical interferometer with the periodic transmittance function as the spectral discriminator to separate aerosol Mie scattering signals and molecular Rayleigh scattering signals excited by the MLM pulsed lasers, such as Mach-Zehnder interferometer, Michelson interferometer, Fabry-Perot etalon and so on. In this paper, we deduce a novel algorithm for retrieving aerosol backscattering coefficient, optical depth, and aerosol extinction coefficient in the application of the MLM HSRL, in which the lidar returns should be considered as a quasi-monochromatic light. Under such a condition, the effective transmittance of Mach-Zehnder interferometer is a function of the complex degree of coherence, which plays an important role in the retrieval algorithms of aerosol optical properties. The retrieval algorithms of aerosol backscattering coefficient, optical depth and aerosol extinction coefficient based on the complex degree of coherence are presented in detail and their correctness is verified by the system simulation using an experimental Mie-Rayleigh lidar returns. Meanwhile, the absolute errors of the measurements of aerosol backscattering coefficient and optical depth are analyzed from the systematic errors and random errors. The simulation results show that the presence of aerosol layers or cloud layer deteriorates considerably the accuracy of the retrieved aerosol backscattering coefficient and optical depth, and the total absolute error of aerosol backscattering coefficient is ignored, as well as the total absolute error of optical depth can be controlled within 0.4 in the majority of the lidar data when the relative error of δ is within 20%. Both measurement examples and continuous observations from the constructed MLM HSRL have proven that the MLM HSRL has the capability in the application of fine detection of aerosol optical properties. [ABSTRACT FROM AUTHOR]

• Calculating and analysing the different biases of T a for delicately correcting extinction coefficient. • Using threshold correction method to correct the error caused by the derivation of T a , and the remaining extinction coefficient is interpolated after threshold correction. • A dual-channel FPE is designed and used to extract aerosol Mie scattering signal and suppress Cabannes–Brillouin scattering in N HSRL. • The extinction coefficient profiles of three cases of severe haze day, moderate haze day and mild haze day were detected and retrieved by the N HSRL. It is difficult to independently obtain aerosol optical parameters at the near-infrared wavelength using lidar. A new high-spectral-resolution technology is proposed to obtain the aerosol extinction coefficient profile at 1064 nm. The high-spectral-resolution detection method by extracting Mie scattering and suppressing Cabannes–Brillouin scattering is applied in the lidar at 1064 nm to improve the detection signal-to-noise ratio. The system parameters of near-infrared high-spectral-resolution LiDAR (N HSRL) must be calibrated in this method; then, the optical parameters are accurately deduced. The effect of the system parameters (transmittances of the spectral filter for molecule and aerosol) on the detection results in this method is discussed and analysed. The transmittance of the spectral filter for aerosol scattering is a key parameter in the retrieval of the extinction coefficient, and the sensitivity of the inversion results to the transmittance is analysed and discussed. The method to distinguish the large deviation data of the extinction coefficient is discussed and provided, and the third derivative of the optical thickness profile is adopted to determine the data. According to the characteristics of the inversion signal, the method to correct the extinction coefficient profile is also presented. The correction algorithm can obviously increase the inversion accuracy of the extinction coefficient. The 1064-nm N HSRL Lidar was developed at Xi'an University of Technology. A dual-channel Fabry-Perot Etalon was designed and used to extract the aerosol Mie scattering signal and suppress Cabannes–Brillouin scattering in this N HSRL. The N HSRL lidar observations were performed, and extinction coefficient profiles at 1064 nm were obtained. The results demonstrate that the method can obtain an accurate profile of the extinction coefficients. [ABSTRACT FROM AUTHOR]

• Neural network is designed to retrieve extinction coefficient from lidar signal. • The initial weights and thresholds of neurons are optimized by genetic algorithm. • The applicability of the optimized network is verified by experiments. Mie lidar is a powerful tool for detecting the optical properties of atmospheric aerosols. However, there are two unknown parameters in the Mie lidar equation: the extinction coefficient and the backscattering coefficient. In the common methods for solving the equation, it is necessary to make assumptions about the relationship between the two unknown parameters. These assumptions will reduce the detection precision of extinction coefficient. In view of this, the back propagation (BP) neural network is used to retrieve extinction coefficient from the Mie scattering signal of lidar. Firstly, the structure and main parameters of the BP network are designed according to the practical application. In order to improve the convergence speed and prevent falling into local minima, the initial weights and thresholds of BP network are optimized by genetic algorithm (GA). Then the GA-BP network is trained with Mie scattering signal and the extinction coefficient retrieved by Raman method. Thus the mathematical relationship between Mie scattering signal and the extinction coefficient is stored in the BP network. The trained GA-BP network is then used to retrieve the extinction coefficient from Mie scattering signal in different conditions and the applicability of the GA-BP network is researched. The research will promote the development of Mie lidar retrieving algorithm. [ABSTRACT FROM AUTHOR]