Fluorescence Lidar Research Articles

Remote Sensing of Plant Fluorescence Spectrum and Lifetime by Laser-induced Fluorescence Lidars

Remote Sensing of Plant Fluorescence Spectrum and Lifetime by Laser-induced Fluorescence Lidars

Analysis of relative error in detection caused by signal-induced noise in Na lidar system

Signal-induced noise (SIN) in a photomultiplier tube (PMT) introduces bias into the Na density results that are retrieved from the backscattered signals of Na resonance fluorescence lidar systems. The response characteristics of a PMT when stimulated by a series of light pulses with a fixed width of 1 μs are therefore used to develop a precise SIN model to estimate the relative error caused by SIN. Unless the strong signals that are returned from the lower atmosphere are excluded, the measured density results are always smaller than the actual values, and the resulting relative error may be 50% or more. Three potential solutions to reduce the SIN were quantified for comparison, including use of a chopper system, use of a gated circuit, and separation of the laser beam and the telescope receiver. When optimized parameters are used for these technologies, the relative error can then be reduced to less than 2%.

POSEIDON: An Analytical End-to-End Performance Prediction Model for Submerged Object Detection and Recognition by Lidar Fluorosensors in the Marine Environment

An analytical end-to-end model is developed to predict the performance of underwater object recognition by means of light detection and ranging (lidar) fluorosensors, as an aid to underwater lidar mission planning and system design. The proposed Performance prediction mOdel for Submerged object dEtection and recognitIon by liDar fluOrosensors in the marine eNvironment (POSEIDON) reproduces the overall end-to-end fluorescence lidar system chain—from signal generation, to signal propagation, acquisition, and processing. The goal is assessing the performance that may be obtained for spectral recognition of an underwater object in various operational scenarios in terms of several different performance metrics. In addition to the performance prediction models developed in the literature for airborne lidar bathymetry, POSEIDON embeds a novel comprehensive signal simulator that accounts for inelastic scattering phenomena as well as a signal processing module designed ad hoc to accomplish spectral recognition of an underwater object with respect to a data base of objects of interest spectrally characterized by their fluorescence spectral signatures . Test cases with a lidar system arranged in two configurations and several objects submerged at various depths in different Cases I and II waters were reproduced and explored. Results obtained within a Monte Carlo simulation framework provide proof-of-concept of POSEIDON performance forecasting capabilities for underwater object recognition.

Demonstration of an iron fluorescence lidar operating at 372 nm wavelength using a newly-developed Nd:YAG laser.

We report on the development of a pulsed neodymium-doped yttrium aluminum garnet (Nd:YAG) laser operating at a 1116nm wavelength. Because the third harmonic is within a few gigahertz of the 372nm absorption line of iron, this laser system represents an alternative to alexandrite lasers commonly used in iron fluorescence lidars. With our prototype, we achieved a 0.5W at 372nm wavelength and a 100Hz pulse repetition frequency. As a proof of concept, we show iron density measurements, which have been acquired using the novel lidar transmitter.

Experimental tests and radiometric calculations for the feasibility of fluorescence LIDAR-based discrimination of oil spills from UAV

This paper presents experimental tests and radiometric calculations for the feasibility of an ultra-compact fluorescence LIDAR from an Unmanned Air Vehicle (UAV) for the characterisation of oil spills in natural waters. The first step of this study was to define the experimental conditions for a LIDAR and its budget constraints on the basis of the specifications of small UAVs already available on the market. The second step consisted of a set of fluorescence LIDAR measurements on oil spills in the laboratory in order to propose a simplified discrimination method and to calculate the oil fluorescence conversion efficiency. Lastly, the main technical specifications of the payload were defined and radiometric calculations carried out to evaluate the performances of both the payload and the proposed discrimination method.

Effects of intrinsic fluorescence on biological aerosols detection accuracy of lidar

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 300nm to 800nm, where the fluorescence was induced by a pulsed laser at 266nm. 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.

Ultraviolet laser-induced fluorescence lidar for pollen detection

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 250mm diameter custom telescope was used to receive optical spectra from 260 nm–560nm excited by 266nm, and R7506 Photomultiplier tubes for two linear orthogonal polarization applications at 532nm. 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 particlesL−1 and 1 particlesL−1 at daytime and nighttime within a range of 1.0km, which is capable of identify a minimum concentration of pollen grains at 903 particlesL−1 and 10 particlesL−1 at daytime and nighttime within a range of 5.0km.

Effect of fluorescence characteristics and different algorithms on the estimation of leaf nitrogen content based on laser-induced fluorescence lidar in paddy rice.

Paddy rice is one of the most significant food sources and an important part of the ecosystem. Thus, accurate monitoring of paddy rice growth is highly necessary. Leaf nitrogen content (LNC) serves as a crucial indicator of growth status of paddy rice and determines the dose of nitrogen (N) fertilizer to be used. This study aims to compare the predictive ability of the fluorescence spectra excited by different excitation wavelengths (EWs) combined with traditional multivariate analysis algorithms, such as principal component analysis (PCA), back-propagation neural network (BPNN), and support vector machine (SVM), for estimating paddy rice LNC from the leaf level with three different fluorescence characteristics as input variables. Then, six estimation models were proposed. Compared with the five other models, PCA-BPNN was the most suitable model for the estimation of LNC by improving R2 and reducing RMSE and RE. For 355, 460 and 556 nm EWs, R2 was 0.89, 0.80 and 0.88, respectively. Experimental results demonstrated that the fluorescence spectra excited by 355 and 556 nm EWs were superior to those excited by 460 nm for the estimation of LNC with different models. BPNN algorithm combined with PCA may provide a helpful exploratory and predictive tool for fluorescence spectra excited by appropriate EW based on practical application requirements for monitoring the N status of crops.

Seasonal variations of meteoric potassium layer over Beijing (40.41°N, 116.01°E)

AbstractA dual‐wavelength resonance fluorescence lidar facility, operating at 770 nm and 589 nm, was set up in the midlatitude of East Asia, Beijing (40.41°N, 116.01°E), to detect the upper atmospheric potassium and sodium layers simultaneously. This fluorescence lidar system has been operational for 220 nights, clocking 1250 h in total from November 2010 to October 2011 and May 2013 to April 2014. The observations reveal that the potassium layer shows considerable semiannual seasonal variations. Specifically, the column and peak densities vary semiannually with maxima in winter and summer. The centroid height displays semiannual variation, reaching maxima in spring and autumn. The RMS width has a slight semiannual seasonality with maxima in July and December. The seasonal behavior of the potassium layer in Beijing is similar to that in other potassium lidar sties. However, the unexpected difference is that the column and peak densities of the potassium layer are extremely large in winter, compared to the maximum values in summer.

荧光偏振短距激光雷达测量生物战剂/气溶胶

荧光偏振短距激光雷达测量生物战剂/气溶胶

Spatial variability of concentrations of chlorophyll a, dissolved organic matter and suspended particles in the surface layer of the Kara Sea in September 2011 from lidar data

The article presents results of underway remote laser sensing of the surface water layer in continuous automatic mode using the UFL-9 fluorescent lidar onboard the R/V Akademik Mstislav Keldysh during cruise 59 in the Kara Sea in 2011. The description of the lidar, the approach to interpreting seawater fluorescence data, and certain methodical aspects of instrument calibration and measurement are presented. Calibration of the lidar is based on laboratory analysis of water samples taken from the sea surface during the cruise. Spatial distribution of chlorophyll a, total organic carbon and suspended matter concentrations in the upper quasi-homogeneous layer are mapped and the characteristic scales of the variability are estimated. Some dependencies between the patchiness of the upper water layer and the atmospheric forcing and freshwater runoff are shown.

Simulation of laser induced fluorescence lidar detecting system

Simulation of laser induced fluorescence lidar detecting system

不同紫外波段激发生物气溶胶荧光雷达系统性能分析

不同紫外波段激发生物气溶胶荧光雷达系统性能分析

Excitation Wavelength Analysis of Laser-Induced Fluorescence LiDAR for Identifying Plant Species

Laser-induced fluorescence (LIF) is an active technology that is closely related to excitation wavelength (EW). This study has mainly analyzed the performance of LIF LiDAR with different EWs in distinguishing plant species. The 355-, 460-, and 556-nm lasers were utilized to excite leaf fluorescence. The fluorescence signals were measured by the LIF system built in the laboratory. Subsequently, principal component analysis combined with back-propagation neural network was used to analyze fluorescence spectra. For the three EWs, the overall identification rates of the eight plant species were 75%, 80%, and 87.5%. However, when the plant species of the same genus were taken as a category, the overall classification rates were 92.5%, 81.3%, and 86.3%. Experimental results demonstrated that, when the plant species of the same genus were regarded as a category, 355 nm was the optimal EW. However, 556 nm was superior to 355 and 460 nm in the identification of plant species of the same genus.

Laser Remote Sensing of Vegetation Cover Using Reflection Coefficients Measurement Data

One of the promising applications of laser remote sensing is a remote control of the vegetation cover. Adverse external factors, lack of fertilizers, and pollution lead to the inability of the normal development of plants. To provide a visual control of such conditions of the vegetation cover at the early stages is often difficult. For this reason it is a relevant task to develop the remote sensing systems to detect plant stress conditions as the indicators of an insufficient nutrient level, pollutants available in the soil, etc. An effective method of remote control of the vegetation conditions is that of laser-induced fluorescence. However, the laser fluorescent method of control has a drawback: for the majority of fluorescent lidars due to small value of the fluorescence cross sections an attainable range of the confident detection of fluorescence signal today is of 100-150 m. Therefore, the relevant objective is to integrate the fluorescent lidar with other optical range equipment that enables remote sensing of vegetation condition from an aircraft at an altitude of several kilometers (with high altitude of flight the scanning equipment provides sensing a greater bandwidth on the earth's surface). The paper analyses the laser remote system capabilities for sensing the vegetation conditions using the measurement data of vegetation reflection coefficients at various wavelengths. It shows that the laser remote sensing system is capable to control vegetation at two radiation wavelengths - one in the visible spectral range (for example, 0.532 mm), and the other - in the near infrared spectral range (e.g. 0.8 ... 0.9 mm). A potential delivery aircraft altitude for the active remote sensing system of vegetation conditions is estimated using the measurements of vegetation reflection coefficients. It is shown that for the wavelength of 0.532 μm in the visible range the limit height of sensing (with realistically attainable now hardware parameters) is about 4 km. For the wavelength of 0.8 ... 0.9 μm in the near infrared range (with the same laser pulse power source) the limit sensing height is higher (in the infrared range the reflection coefficient of vegetation is higher).

Combined use of LIDAR and hyperspectral measurements for remote sensing of fluorescence and vertical profile of canopies

Se presenta el desarrollo de un nuevo sistema lidar (LASVEG) para la teledetección aerotransportada de la fluorescencia de la clorofila (ChlF) y el perfil vertical del dosel. Mediante la combinación de la fluorescencia inducida por láser (LIF), la fluorescencia inducida por el sol (SIF) y la distribución de la altura del dosel, el nuevo instrumento permitirá la evaluación simultánea de la producción primaria bruta (GPP), la eficiencia de la fotosíntesis y las reservas de carbono por encima del nivel del suelo. Se discuten cuestiones técnicas del desarrollo del lidar fluorescencia y se presentan las prestaciones previstas.

Research and analysis on lidar performance with intrinsic fluorescence biological aerosol measurements

Biological aerosols which could cause diseases of human beings, animals and plants, are living particles suspended in the atmosphere. Ultraviolet laser induced fluorescence has been developed as a standard technique used to discriminate between biological and non-biological particles. As an effective tool of remote sensing, fluorescence lidar is capable of detecting concentration of biological aerosols with high spatial and temporal resolutions. Intrinsic fluorescence, one of the most important characteristics of biological aerosols, has quite a large effect on the performances of fluorescence lidar. To investigate the effects of intrinsic fluorescence on biological aerosols, we design an ultraviolet laser induced fluorescence lidar at an excited wavelength of 266 nm, with a repetition rate of 10 Hz. Fluorescence signals are collected by a Cassegrain telescope with a diameter of 254 mm, in which fluorescence spectra of 300-800 nm are mainly considered. A spectrograph and a multichannel photomultiplier tube (PMT) array detector are employed to achieve the fine separation and highefficiency detection of fluorescence signals. According to the present configuration, we perform a series of simulations to estimate the measurement range and the concentration resolution of biological aerosols, with a certain pulse energy. With a relative error less than 10%, theoretical analysis shows that designed fluorescence lidar is able to detect the biological aerosols within a range of 1.5 km at a concentration of 1000 particles·L-1. When the detection distance enlarges to 2.1 km, detectable wavelength range is limited to 300-310 nm. In addition, the lidar is capable of identifying minimum concentrations of biological aerosols with 2 particles·L-1 and 4 particles·L-1 at fluorescence wavelengths of 350 nm and 600 nm, respectively, where the induced pulse energy is set to be 60 mJ and detected range 0.1 km. With setting energies of 40 mJ and 20 mJ, minimum concentrations of biological aerosols decrease to 3 particles·L-1 and 6 particles·L-1, respectively, at a fluorescence wavelength of 350 nm. The relative error of minimum concentration resolution is about 2 particles·L-1, increasing rapidly with range. For a fluorescence wavelength of 600 nm, both the minimum concentration and the relative error show relatively high values, 5 particles·L-1 at 40 mJ and 10 particles·L-1 at 20 mJ, where the relative errors are found to be 2 particles·L-1 and 4 particles·L-1, respectively. The results prove that a shorter intrinsic fluorescence wavelength has a better effect on biological aerosol measurement. We believe that a proper intrinsic fluorescence wavelength will further improve the detection accuracy of biological aerosols.

Simulation of fluorescence lidar for detecting oil slick

In order to measure the oil pollution on water surface, a fluorescence lidar model system based on laser induced fluorescence is put forward for detecting oil slick. The system model and fluorescence detecting principle are described in detail. According to the properties of detected material, wavelength of laser and filter of receiving system are adopted to ensure that the lidar system is operated at the peak wavelength. Following the development trend of miniaturization in the world, using single laser and intensified charge-coupled devices, a small fluorescence detecting system is designed. FTSS 350-50 laser made by CRYLAS company, with compact dimension, low weight and excellent energy efficiency, and PI-MAX4 intensified charge-couple devices made by Princeton Instruments company, with good time resolution characteristic, are selected to produce laser as a launch device and to inspect fluorescence lifetime and capture image as a receiving device, respectively. The laser excitation wavelength, the energy of laser, the center wavelength and bandwidth of filter, the received echo fluorescence signals, the detected concentration and distance are discussed in detail by means of the instance for oil on water surface. Through analyzing the relationship between the energy of laser single pulse and the detection concentration and by combining with the parameters of fluorescence lidar system and fluorescence lidar equation, the detecting ability of system model, signal-to-noise ratio, etc. are simulated particularly. A numerical simulation of the signal-to-noise ratio of the fluorescence particles is conducted particularly so that the detectable capacity of system designed could be described better. The results show that the signal-noise ratio of system which is operated during the night is superior to in daytime in the same single pulse energy case and that the detected range becomes gradually longer as the energy of laser improves with the same signal-noise ratio case. The required single pulse energy to support system is calculated, and further verifies the feasibility of the lidar system. The test results of the sample show that in the daytime, the design of fluorescence lidar model, with a Nd:YAG laser of 50 J single pulse energy and 355 nm wavelength serving as an excitation light source, with a collection device placed at a distance of 7 m, can satisfy the requirements for detecting oil pollution on the water surface in laboratory, and its signal-noise ratio can reach 10. In view of the actual surface fluorescence lidar detection requirements, the method of increasing the laser power is proposed. A real system with 50 mJ single pulse energy at a distance of 230 m has nearly the same performance as the laboratory lidar system, which could provide a valuable guidance for designing a real system.

Injection Seeded Laser for Formaldehyde Differential Fluorescence Lidar

We describe the design and development of an injection seeded Nd:YVO4 laser for use in a differential fluorescence lidar for measuring atmospheric formaldehyde profiles. A high repetition rate Q-switched laser is modified to accept injection seed input to spectrally narrow and tune the output. The third harmonic output is used to excite formaldehyde (HCHO) fluorescence when tuned to a HCHO absorption line. Spectral confirmation is made with the use of a photoacoustic cell and grating spectrometer.

Study on Bioagents/Bioaerosols Standoff Detection by Lidar

Scattering, fluorescence and polarization are the important data source for bioagent or bioaerosol time-space observation and identification. This paper stated and discussed the theory and data inversion principles for Mie scattering, laser induced fluorescence and polarization sensing Lidar. The sensing and data inversion results for bioagent/bioaerosol extinction coefficient, horizontal linear depolarization ratio were also demonstrated. The signal and SNR simulation of fluorescence lidar were also demonstrated. The sensing results revealed that the three kinds of detecting technology approaches are reasonable and potential for bioagent/bioaerosol characterization and recognition.