Laser induced breakdown spectroscopy (LIBS) is a kind of laser ablation spectrum analysis technology, which has the advantages of small sample damage, fast detection speed and simultaneous detection of multiple elements. In this paper, a LIBS system based on passive Q-switched laser is designed, which is used to carry out marine heavy metal detection research. Aiming at the two or more laser pulses that the laser may generate in a single pumping cycle, a laser pulse control module is designed in this paper to analyze and judge the number of laser pulses, and obtain good experimental results. Using this LIBS system to output single-pulse and double-pulse lasers to detect samples of seawater and shells in different regions, we can detect the presence of characteristic spectral lines of elements such as Na, Mg, Ga and other elements in seawater. At the same time, the characteristic spectra of Cu, Al and some other elements are found in the shell samples, which suggest that there are heavy metal pollution components in the shells.
KEYWORDS: Imaging systems, LIDAR, Analog electronics, 3D image processing, 3D acquisition, Image processing, 3D image reconstruction, Signal processing, Control systems, Process control
A precise delay system for a streak tube imaging lidar (STIL) is developed. Two delay schemes are designed that are suitable for long- and short-distance lidar imaging. The digital scheme delay can reach 100 μs, and its precision is <6 ns; the analog scheme delay can reach 1200 ns and its precision is <1 ns. Using the STIL system, three-dimensional (3-D) imaging experiments are carried out on land targets at about 2.3-km range and underwater targets at about 25-m range. The experimental results show that the designed delay device can produce precise delay times and effectively verify the 3-D imaging quality of the STIL. This device also has the advantages of stable operation, being more compact, and requiring less power than existing instruments.
Laser Induce Fluorescence (LIF) is a widely used new telemetry technology. It obtains information about oil spill and oil film thickness by analyzing the characteristics of stimulated fluorescence and has an important application in the field of rapid analysis of water composition. A set of LIF detection system for marine oil pollution is designed in this paper, which uses 355nm high-energy pulsed laser as the excitation light source. A high-sensitivity image intensifier is used in the detector. The upper machine sends a digital signal through a serial port to achieve nanoseconds range-gated width control for image intensifier. The target fluorescence spectrum image is displayed on the image intensifier by adjusting the delay time and the width of the pulse signal. The spectral image is coupled to CCD by lens imaging to achieve spectral display and data analysis function by computer. The system is used to detect the surface of the floating oil film in the distance of 25m to obtain the fluorescence spectra of different oil products respectively. The fluorescence spectra of oil products are obvious. The experimental results show that the system can realize high-precision long-range fluorescence detection and reflect the fluorescence characteristics of the target accurately, with broad application prospects in marine oil pollution identification and oil film thickness detection.
A high frame rate streak tube imaging lidar (STIL) for real-time 3D imaging of underwater targets is presented in this paper. The system uses 532nm pulse laser as the light source, the maximum repetition rate is 120Hz, and the pulse width is 8ns. LabVIEW platform is used in the system, the system control, synchronous image acquisition, 3D data processing and display are realized through PC. 3D imaging experiment of underwater target is carried out in a flume with attenuation coefficient of 0.2, and the images of different depth and different material targets are obtained, the imaging frame rate is 100Hz, and the maximum detection depth is 31m. For an underwater target with a distance of 22m, the high resolution 3D image real-time acquisition is realized with range resolution of 1cm and space resolution of 0.3cm, the spatial relationship of the targets can be clearly identified by the image. The experimental results show that STIL has a good application prospect in underwater terrain detection, underwater search and rescue, and other fields.
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