Atmospheric aerosol refers to the stable mixing system composed of solid and liquid particles evenly dispersed in the atmosphere, and the particles are collectively referred to as aerosol particles. Aerosol particle detection is an important aspect of environmental monitoring. With the development of computer technology and holographic technology, the resolution of holographic measurement technology continues to improve. At present, digital holography can be used to measure the tiny displacement, deformation and vibration of opaque objects. In this paper, aluminum oxide powder is used to simulate aerosol particles. Aerosol particles are recorded by digital holography and holograms of aerosol particles are obtained. Finally, the shape and size of aerosol particles can be obtained.
Optical tomography imaging is widely used in target-detection, aerospace precision instrumentation and geological material detection for its non-contact, long-distance and high-precision imaging characteristics. Due to the different application range and structural design of the tomography system, the inevitable inadequate projection data and the offset of the rotation center may occur in the actual acquisition, which may cause artifacts and unclearness in the reconstructed image. In this paper, based on the research of image reconstruction algorithm, the paper compares filter back projection algorithm with iterative algorithm and analyzes effects of the reconstruction process with iterative algorithm under multiple parameters. Determining the appropriate weighting model, iteration number and relaxation factor, etc. Combined with high quality initial image and convex set constraints, an optimized SART algorithm is proposed. The experiment uses the optimized SART algorithm for image reconstruction. By comparing the image evaluation parameters with sharpness and average gradient, it is verified that the construction image with the optimized SART is better and clearer than those with the unoptimized SART and the simple filtered back projection algorithm.
The detection of underwater microorganisms is an important means to detect water quality. The determination of water quality can be completed by detecting the species, quantity and density of microorganisms in water. In order to detect underwater microorganisms, a method of measuring underwater microorganisms by digital holography is presented. Paramecia were measured and their morphology was obtained by digital holographic imaging, so as to detect and identify underwater microorganisms.
The atmosphere is full of liquid and solid particles, both man-made and natural. Atmospheric particles play a key role in weather, climate and biological health. Therefore, the accurate measurement of atmospheric particles is of great significance. Digital holography, as a new generation of imaging technology, has the advantages of simple and stable structure, three-dimensional imaging, and the ability to distinguish laminated particles. Digital holography technology has been widely used in the field of three-dimensional morphology measurement, interferometry, nondestructive testing, holographic microscopy, particle field measurement and other fields. In the field of particle field measurement, most optical particle field measurement technologies can only measure spherical particles to obtain the statistical distribution of particle concentration and diameter, such as laser scattering method and phase doppler method.Digital holography can obtain the morphology details, particle size parameters and three-dimensional spatial distribution spectrum of each particle in the particle field. On the basis of the original device, the two-views hologram is recorded by adding a reflector. The coordinates of the particles along the optical axis will be determined by the position of the reflector and the position of the reflected image.
The digital holography technology is based on holography. A photodetector device is used instead of a holographic dry plate as a recording medium. The light intensity and phase information of the object is recorded, and the reproduced image is obtained by using a computer to realize the holographic reproduction process. Digital holography can perform noncontact, high-quality measurements and can obtain three-dimensional position information. This paper presents an off-axis digital holographic underwater microbiological detection method based on Jamin interferometer. For the identification of underwater microorganisms, the Euclidean distance identification method based on Hu invariant moments was used to identify underwater microorganisms. The experimental results show that the off-axis digital holography system constructed in this paper can clearly capture the underwater microorganisms, and effectively identify the paramecium and the feasibility of the verification system and algorithm.
Infrared imaging technology plays an irreplaceable role in early warning detection, intelligence reconnaissance, night vision sighting, fire control guidance, precision strike and electronic confrontation. The optical tomography imaging system, obtaining a plenty of target object information with non-invasive, can realize long-distance and high-resolution imaging. The system has important significance for accurate target recognition and detection. This paper aims to combine the two for the purpose of research for optical guidance of large field of view, high spatial resolution infrared imaging methods. In this paper, the principle of tomography and the commonly used filtered back-projection reconstruction algorithm are introduced firstly. Then the innovative infrared tomography system construction design is proposed. According to this design, a set of infrared tomography imaging device is successfully built. An infrared tomographic image of the target was photographed and reconstructed. It has a great significance to the research of infrared tomography.
In the artificially affected weather, the detection of cloud droplets particles provides an important reference for the effective impact of artificial weather. Digital holography has the unique advantages of full-field, non-contact, no damage, real-time and quantification. In this paper, coaxial digital holography is used to record the polyethylene standard particles and aluminum scrap, and some important parameters, such as three-dimensional coordinate spatial distribution and particle size, will be obtained by the means of analyzing the digital hologram of the particle. The experimental results verify the feasibility of the coaxial digital holographic device applied to the measurement of the cloud parameters, and complete the construction of the coaxial digital holographic system and the measurement of the particles.
On the basis of the conventional Jamin interferometer,the improved measuring method is proposed that using a polarization type reentrant Jamin interferometer measures atmospheric aerosol absorption coefficient under the photothermal effect.The paper studies the relationship between the absorption coefficient of atmospheric aerosol particles and the refractive index change of the atmosphere.In Matlab environment, the variation curves of the output voltage of the interferometer with different concentration aerosol samples under stimulated laser irradiation were plotted.Besides, the paper also studies the relationship between aerosol concentration and the time required for the photothermal effect to reach equilibrium.When using the photothermal interferometry the results show that the time required for the photothermal effect to reach equilibrium is also increasing with the increasing concentration of aerosol particles,the absorption coefficient and time of aerosol in the process of nonequilibrium are exponentially changing.
In this paper, an improved Interferometer was introduced which based on traditional Jamin Interferometer to solve the twin image where appear in on-axis holographic. Adjust the angle of reference light and object light that projected onto the CCD by change the reflector of the system to separate the zero order of diffraction, the virtual image and the real image, so that could eliminate the influence of the twin image. The result of analysis shows that the system could be realized in theory. After actually building the system, the hologram of the calibration plate is reconstructed and the result is shown to be feasible.
The rotation center of the optical tomography is not strict in the actual device, resulting in the deviation of the rotation center, so that the final projection image reconstruction effect is not ideal. The method proposed in this paper introduces the sampling and fitting circle method on the basis of the original projection sinusoidal center calibration method, makes a preliminary calibration of the rotation center and makes it more accurate with the gradient operator after the center of the projection sinusoid is positioned. A further central calibration of the object imaging in the optical path transmission is made at the center of the detector target surface according to the gradient. Experiments show that the center position of this method is more accurate than the original sinusoidal calibration and has a reliable basis. Using the gradient operator to judge the effective image clarity, the final reconstructed image also has high resolution and anti-jamming. The feature recognition rate of the image has greatly improved. The experimental results have made a great contribution to obtaining clear and effective information.
The cloud in the high altitude is usually in the gas-liquid mixed state, this paper simulates the environment of the cloud particle using bubble field in the liquid. The paper research the gas-liquid mixture via measuring the size and 3D position of the bubble using a digital in-line holographic imaging system. The design of the optical system and the algorithm of reconstruction, recognition and extraction about the digital hologram is presented. The digital holography deserves to be selected as the projection to measure the bubble field because of advantages such as being able to record and reconstruct the three-dimensional position information, avoiding disturbing the object and insuring the instantaneity during the measurement. The optical system and the algorithm about the digital program have been completed, the hologram of bubbles in the liquids recorded by CCD, the hologram reconstruction using the digital hologram after denoising processing is accomplished. The character of cloud particles can be measured by using holography after analyzing the parameter of the bubbles.
In terms of climate science, getting the accurate cloud particle sizes, shape and number distributions is necessary for searching the influence of cloud on the environment, radiative transfer, remote sensing measurements and understanding precipitation formation. Many methods and instruments have been developed to measure cloud particles, yet there is still restricted to one-dimensional or two-dimensional projections of particle positions, unable to get the three-dimensional information of the spatial distribution of particles. In-line holography is particularly useful for particles field measurements, because it can directly get the three-dimensional information of the particles and quickly access and storage holographic image. In this paper, the main work is using digital in-line holographic system to measure simulated cloud particles in the laboratory. For digital recording hologram reconstructing, we consider the image intensity in conjunction with the edge sharpness of the particles, to obtain an automatically selected threshold of each particle. Using the threshold, we can get a binary image to identify the particles and separate the particles from background, and then get the information such as the location, shape, particle size of particles. The experimental results show that the in-line digital holography can be used to detect the cloud particles, which can gain many parameters of the simulated cloud particles in the plane perpendicular to the optical axis, and can estimate volume parameters of the simulated cloud particles. This experiment is a basis for the further in situ detection of atmospheric cloud particles.
Due to the structure of clouds has so many complicated factors, the cloud seeding area is difficult to accurately determined. How to accurately understand the structures of the particle parameters has great significance for weather modification. Digital holographic technology is widely used in particle measurement, because it can realize the three-dimensional particle field measurement and get detail parameters. This paper, based on the research of the holographic reconstruction and image processing algorithm, calculate the equivalent diameter of particle, and obtain the distribution of the particles, for the estimation of the population parameter of particle is put forward a feasible method.
This paper put forwards a new optical tomographic imaging system, which consists of the rotating periscope system and modulating plate with 65 slits. One-dimensional signals which are divided by modulating plate through the rotating periscope system are collected by photon detector. The paper analyzes the principle of filter back projection (FBP), and chooses the filter that fits the system. It verifies the feasibility of this system by the actual simulation. Choose the circular hole and the calibration image as the target image in scanning experiment, in result of finding that the feature of reconstruction result is obvious, but information of edges is fade. This system plays an important role in developing feature extraction of surface.
In terms of weather modification, detection of cloud droplet particles, which is one of the important measurements, will provides an important reference for artificial weather modification. Digital holographic technology, for that it can realize the three-dimensional particle field measurement and get detail parameters of particle, is widely used in particle measurement along with the high development of modern high resolution CCD and computer technology. In this text , particle of cloud droplet simulated in the laboratory were recorded. By using the in-line digital holographic to obtain the digital holographic image of cloud droplets particles, and single feature parameters (including the shape, size, ovality) of the cloud droplets particles by calculating . It laid a foundation for the future research of cloud group particle characteristics of particle field.
Optical tomography imaging had the characteristics of high resolution. The rotating periscope system and modulating plate with 65 slits were designed. Filter back projection (FBP) algorithm was applied to the one-dimensional signals, which were obtained by multi-angle scanning in modulating plate, to reconstruct two-dimensional image. Single pixel photoelectric sensor has high frequency response and can acquire high speed real-time signal. This work had carried on the simulation and experiment about scanning system based on the analysis and determination about the modulating plate’s parameters, and verify the feasibility of scanning system. In this paper, the method plays an important role in developing novel target tracking system and provides deep foundation for deeper experimental research.
This paper studies the basic principle of laser photothermal interferometry method of aerosol particles absorption coefficient. The photothermal interferometry method with higher accuracy and lower uncertainty can directly measure the absorption coefficient of atmospheric aerosols and not be affected by scattered light. With Jones matrix expression, the math expression of a special polarization interferometer is described. This paper using folded Jamin interferometer, which overcomes the influence of vibration on measuring system. Interference come from light polarization beam with two orthogonal and then combine to one beam, finally aerosol absorption induced refractive index changes can be gotten with four beam of phase orthogonal light. These kinds of styles really improve the stability of system and resolution of the system. Four-channel detections interact with interference fringes, to reduce the light intensity ‘zero drift’ effect on the system. In the laboratory, this device typical aerosol absorption index, it shows that the result completely agrees with actual value. After heated by laser, cool process of air also show the process of aerosol absorption. This kind of instrument will be used to monitor ambient aerosol absorption and suspended particulate matter chemical component. Keywords: Aerosol absorption coefficient; Photothermal interferometry; Suspended particulate matter.