With the rapid development of precision automation and intelligent equipment industry, the need of miniaturized and high-precision grating displacement sensors is increasing. It is still a challenge for highly reliable mini sensors due to the limitations of current employed light sources, such as their sizes, features, etc. To develop novel grating displacement sensors, light source needs to be met the requirements. Based on the principles of grating signals, we developed a novel grating displacement sensor by employing a Honeywell infrared LED as the light source. The influence of the main parameters (e.g. divergence angle, width of light source, etc.) of the infrared LED light source on the grating Moiré Fringes has been analyzed in detail. The intensity distribution of the Moiré light field model has also been established to estimate the quality of the grating signals with new light source. Both mathematical modeling and experimental results verify the feasibility of the design showing two clear orthogonal sinusoidal signals. Compared with traditional light sources (visible point light source), the infrared LED light source can significantly shorten the grating optical structure, thereby facilitating the miniaturization of the grating sensor. Due to the transmission characteristics of long-wavelength light, the infrared source can both improve the contrast of the Moiré Fringes and the quality of the grating signals. We believe that the designed grating displacement sensor will open a new phase in application with the advantages of infrared LED source, such as stable intensity, long lifetime and low prices.
Aimed to establish a Raman lidar system with high-reliability and high anti-interference performance, an newly all-fiber spectroscopic Raman lidar system was proposed for atmospheric water vapor measurement, in which optical fiber couplers, fiber band-width filters and fiber F-P filters constitute the all-fiber spectroscopic system. On the basis of the design of fiber F-P filters and its transmission analysis, the series connection of optical fiber coupler is designed as fiber optics splitter, which is not only to obtain fiber coupling of the input and output of lidar returns, and also to achieve the optimal energy output ratio at three fiber channels. Furthermore, fiber band-width filters are proposed to replace the dichroic mirrors, and the structure of fiber band-width filters and fiber F-P filters is to constitute the secondary cascade filter system, achieving the fine extraction of interested spectrum and high rejection rate to elastic scattering signals. Preliminary test results indicated that, the energy at the three output ports is %sim;5: 2.5: 2.5, and the two fiber band-width filters are provided with the central wavelength of 606nm and 660nm, the bandwidth of 20nm, and the out of band inhibition of >0.5%, which met the design requirements. The design and results will provide a reliable basis for the integration and experiment of the subsequent all-fiber spectroscopic system.
To realize the improvement of signal-to-noise ratio and rejection rate for elastic Mie-Rayleigh signals, a set of dichroic mirrors and narrow-band interference filters with high efficiency was proposed to constitute a new spectroscopy for atmospheric water vapor, aerosol, and cloud studies. Based on the curves of signal-to-noise ratio at three different channels, the actual rejection rates of elastic Mie-Rayleigh signals at the Raman channels were found to be higher than eight orders of magnitude with the cloudy conditions. Continuous nighttime observations showed that the statistical error of the water vapor mixing ratio was <10% at a height of 2.3 km with an aerosol backscatter ratio of 17. Temporal variations of water vapor and aerosols were obtained under the conditions of cloud and cloud-free, the change relevance between aerosol and water vapor was analyzed, and the growth characteristics of water vapor and aerosols showed a good agreement within the cloud layers. Obtained results indicate achievement of the continuous detection of water vapor, aerosol, and cloud with a high efficiency and stability by Raman lidar.
A dual wavelength micro pulse polarization lidar system is designed, in which Nd:YAG laser at 1064nm and 532nm is employed as the exciting source, to research the depolarization ratio, the lidar ratio and the angstrom coefficient of aerosols. Numerical simulations are performed with the standard atmospheric model to verify the detection ability of the system. The simulation results show that the lidar system is capable of detecting the depolarization ratio of aerosols up to a height larger than 6 km at night and 2 km in the daytime with a sigal to noise ratio of 10. In the meantime, the lidar system can also be used to detect the angstrom coefficient, and can provide important scientific data for studies of the relastionship among these parameters.
Atmospheric aerosol particles influence the Earth’s radiation balance both directly and indirectly. The aerosol size distribution (ASD) is one of the most important microphysical properties. In this paper, the generalized cross-validation (GCV) regularization method is used for the retrieval of ASD from three-wavelength lidar optical data. The numerical simulations are carried out using synthetic backscatter and extinction coefficients. Simulations results demonstrate that the ASD depends on particle refractive index. Choosing the suitable refractive index is crucial to retrieve aerosol size distribution accurately. Moreover, the numerical results show that, for the same refractive index, it is more suitable to retrieve broad ASD, which has larger mode width σ. The GCV regularization method has been tested for a set of experimental data from three-wavelength lidar, which provides backscatter coefficient at 355, 532 and 1064 nm and extinction coefficient at 355 and 532 nm. Experimental result shows that the retrieved size distribution belongs to the urban industrial type and fine mode. The result shows good agreement with the actural atmospheric aerosol size distribution of local area. Both the simulation and the expriment demonstrate that the GCV regularization method is feasible to retrieve the aerosol size distribution.
A portable Micro-pulsed Mie scattering lidar at the laser wavelength of 532 nm has been developed for routine observation of atmospheric optical properties of the lower troposphere, including boundary layer structure, cloud, the distribution of aerosol and horizontal visibility and so on. The configuration of lidar and its design methods including the hardware and software were described in details. The lidar system was controlled by compact computer, including self adjustment for coaxial lidar, three-dimensional scanning, real-time data processing of visualization and inversion online. The experimental results illustrate that the system can measure the atmospheric aerosols up to the range of near 5 km at daytime and up to 15 km at nighttime under the measurement conditions of laser energy of 50 μJ, signal averaging time of 40s, a receiving aperture 254 mm, range resolution of 7.5 m and analog detection model, which can provide scientific measurement data for studying the atmospheric environment change, particularly for resolving the particulate pollutant generation, transmission and diffusion characteristics.
The fringe-imaging Fabry-Perot (FIFP) interferometer and fringe-imaging Mach-Zehnder (FIMZ) interferometer as frequency discriminator for incoherent molecular Doppler wind lidar are proposed, analyzed and compared theoretically respectively. Using ZEMAX software, the FIFP interferometer and FIMZ interferometer are designed and simulated respectively. Compared with Fabry-Perot interferometer (FPI), Mach-Zehnder interferometer (MZI) produces equidistant linear parallel fringes instead of circular rings. The record of the MZI fringe pattern is noticeably easier than that of the FPI and can be performed with a cylindrical lens and focused on a linear CCD array rather than a complex circle to line interferometer optical (CLIO) system. According to the U.S. standard atmospheric model, the transmission, signal-to-noise ratio (SNR), sensitivity and wind error for FIFP and FIMZ systems are simulated respectively. The results show that, the MZI sensitivity is lower than that of FPI, however, the MZI offers 4 times higher transmission, resulting to about 1.4 times smaller wind error in the line-of-sight (LOS) velocity component than that of FIFP. In addition, the MZI can be designed with a compensated field to accept sources of appreciable dimensions without significant performance reduction, which will provide an effective technique for Doppler wind lidar to improve the accuracy of wind velocity measurement by using MZI as frequency discriminator.
The research of ultra-multi-point strain detection is one of the important topics at the forefront of optical fiber sensing technology. A newly ultra-multi-point strain measurement system was designed based on optical time-domain reflectometry (OTDR) and Fiber Bragg Grating. Two distributed feedback (DFB) lasers is proposed as laser source to generate the alternately pulsed light, and transmitted to a serial of fiber Bragg gratings with the same low-reflectivity and bandwidth. By the means of the strength of each reflectance spectrum and its return time of signals, the magnitude and location of strain can be accurately determined, and the numerical simulation shows that more than 1000 FBGs can be multiplexed in OTDR-FBG strain measurement system for a larger strain measurement range. Furthermore, the corresponding driving circuits for nanosecond pulse and temperature control circuits are designed for laser pulse modulation and frequency stabilization control. A OTDR-FBG strain measurement system is developed by using 10 FBGs with the reflectivity of less than 5%, and the system distance resolution of 43 cm is obtained, which verified the feasibility of the system.
Long-term observations of atmosphere aerosol optical properties over Xi’an area have been carried out by a Raman-Mie
lidar and a Micro-pulsed 3D Scanning Mie lidar, which were built at Xi’an University of technology with the laser
wavelength of 355nm and 532nm, respectively. The Raman-Mie lidar is used for observation of the atmospheric
temperature, water vapor and aerosol profiles simultaneously. In order to deeply discuss the temporal-spatial evolution of
the mixed-layer within the urban boundary layer (UBL), the method of combining the absolute minimum of first
derivative and second derivative of the range-squared-corrected signal (RSCS) of lidar was used to retrieve the
mixed-layer depth (MLD). By using continuous observations of 24-hour (THI display), the MLD in temporal and spatial
variation are clearly revealed. Also, the results of continuous observations from July 2006 to October 2011 have been
analyzed for revealing the seasonal cycle and the annual cycle of the MLD. By analyzing the average MLD, it is
obviously shown that the MLD of seasonal cycle is higher in summer than in winter over Xi’an area. Otherwise, by
investigating the relationship of atmospheric boundary layer height, relative humidity and temperature, and the
dependence characteristics and a general disciplinarian between them are then obtained. The achievement is of great
importance for studying the proliferation of urban pollution and obtaining a complete meteorological status of the urban
atmosphere.
An ultraviolet Raman lidar system at 354.7nm laser wavelength has been developed to measure
the elastic scattering signal and the vibrational Raman scattering signal of N2 and H2O for
fine-detection of atmospheric humidity profile. A newly spectroscopic filter structured with a
high-spectral-resolution grating and two narrow band mirrors are used to separate those
backscattering signals finely. The density of humidity is derived from the vibrational Raman
scattering signal of N2 and H2O, the relative humidity profile is obtained combining with the
temperature profile taken simultaneously by Raman temperature lidar. Some preliminary
experiments have been carried out in nighttime at Xi'an area, the wator vapor mixture ratio
vertical profile is analyzed. The experiments results indicate that a measurement error of the
relative humidity less than 10% is obtained within the atmospheric boundary layer under the
condition of laser energy of 300mJ and observation time of 10min.
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