When the camera imaging method and the detector array method are used to obtain the laser spot image after atmospheric transmission, the image sequence will contain the actual spot image information and the background information of the test system. During the data processing, the image sequence needs to be segmented to eliminate Image background information firstly. Considering that the brightness, contrast, and structure of the images collected by the system will change significantly before and after the laser irradiation measurement system, a method of image structure similarity is proposed to segment the background information of the image sequence. The method of dynamic template is used to calculate the similarity of the light spot sequence, and the similarity threshold is set to complete the segmentation and elimination of the background information of the image. Experiments show that the background segmentation method of image sequence based on structural similarity can quickly and accurately achieve segmentation of background information. The research results can provide a certain theoretical basis and method accumulation for establishing a perfect data processing method in the laser parameter measurement system.
Sampling and attenuation of the laser beam to be measured is the first step for detector array target to measure temporal and spatial distribution of laser intensity. Existing sampling attenuation technology is more sensitive to the incident angle of laser beam. In practical applications, sampling angle response characteristics of laser beam can be measured experimentally, and get the coefficient to be corrected. Among them, scattering sampling method is based on scattering parameters of selected sampling material, which can effectively correct sampling angle response in theoretical or simulation stage. In this paper, focusing on angular characteristics of scattering sampling for detector array target, based on bidirectional transmission distribution function, the correlation between the scattering sampling angular characteristics and scattering distribution is derived. Experiments have proved that scattering sampling angle characteristic for detector array target can be expressed in the form of ratio of material scattering distribution function. This characteristic provides a certain guidance for design of scattering sampling angle tolerance for detector array target.
The differential image motion monitor (DIMM) is a widely used instrument for measuring atmospheric coherence length. We studied the feasibility to miniaturize the classic DIMM. By adopting more accurate formulas, the geometry of the classic DIMM can be altered mildly. A mini-DIMM can be developed under this new geometry condition. For example, a mini-DIMM may consist of two 6-cm apertures, located close to each other. We present the validation experiment where astronomical seeing was measured simultaneously by a mini-DIMM and a standard DIMM. Comparisons with a standard DIMM show good agreement between the two instruments.
In order to achieve quantitative measurement of the spatial and temporal distribution of far-field laser spot, it is necessary to solve the calibration problem of the photodetector array target measurement system. For the photodetector array target calibration system, the unit detector is scanned one by one, and the unit detector is regarded as a black box. Its input and output correspond to the voltage pulse amplitude and the energy density of the laser beam respectively, in order to meet the energy density. The measured value of the measured value and the actual value of the project indicator, the segmentation relationship between the energy density of the photodetector and the amplitude of the voltage pulse is derived. The verification test shows that the error of the energy density measurement and the calibration true value of the verification test is less than 15% at a small energy density, and the error is less than 10% at a larger energy density. This calibration method has the advantages of simple operation and high calibration accuracy, and has guiding significance for future photodetector array target calibration technology.
For its better spectral response characterization, higher quantum efficiency and signal-to-noise ratio, camera is more and more used in atmospheric parameters measurement lidar. Camera lidars retrieval atmospheric parameters by analyzing the light column images acquired by the cameras and objectives through gathering the backscatter light of the laser beam. Lidars of this kind usually have higher spatial resolution and better real time performance. However, because of its limited depth of field (DOF), the measurement accuracy of the area out of the DOF is influenced by optical defocus in different degree. In the meantime, it is also not suitable for portable equipments for using small relative aperture receiving objective. Based on improving the design of the receiving objective, a new design scheme is proposed in this paper about improving the optical receiving system of the camera lidar. This scheme can improve the measurement accuracy of the area out of the DOF in traditional structure by using large DOF, large relative aperture offaxis objective and the special using mode of the camera. The optical receiving system designed according to this scheme is more compact and is especially suitable for portable instrument. Furthermore, the relation among the focus length, the distance between laser and objective and the installation angle is also analyzed in this paper. The formula is given at the same time. This scheme is carried out in camera lidar system in laboratory and the results are satisfactory.
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