A Split-Type Reflective Method to Measure the Velocity of the Underwater Weapon
LIU Ji1，2, WU Jin-hui1, YU Li-xia2, ZHANG Jing2, YANG Qi2
1. Science and Technology on Electronic Test and Measurement Laboratory, North University of China, Taiyuan 030051, China
2. School of Information and Communications Engineering, North University of China, Taiyuan 030051, China
Abstract：Dynamic parameter measurement is the essential of performance for special weapons, such as amphibious and underwater special weapons. The information about velocity of moving target underwater is one of the important factors for evaluating underwater weapons performance. There are many disadvantages of the traditional connect measurement method, for example, aluminum foil target and comb target have poor reliability, small effective area and low repeatability in an underwater environment. At the same time, the methods of Doppler and sonar are very expensive. In order to solve these problems, we propose a real-time and non-contact method to obtain weapon velocity parameters based on the split-type reflective and with laser screen as effective area. The law of underwater spectral transmission is determined by analyzing the law of Lambert-Beer and the function of body scattering and other mathematical principles. The optimal laser peak wavelength was obtained. A 1 m-diameter cylinder was created as a scatterer to simulate the scattering of in water. The total number of traced space rays was 1×105. And the light energy of the irradiance at the receiving surface located at 1, 3, 5, and 7 m was obtained. So the optimal peak power of the system laser source was obtained also. On the basis of this, the optical system adopted principle of determining the distance measuring time principle and the one-dimensional retro-reflective technology, which consisted of 532 nm, fiber-coupled semiconductor lase，fiber-coupled laser beam expander used Powell lens and retro-reflector. The laser emission part and the signal processing part were located on the water, and the effective area of the laser screen was located under the water. The laser was emitted and the signal was recovered by the optical fiber. One end of the transmitting optical fiber was coupled with the light source, and the other end of the optical fiber was coupled with the Powell lens to form a fan-shaped light screen under water. One end of the receiving optical fiber was distributed at Powell prism exit, and the other end was coupled with the PIN-type photoelectric sensor. One-dimensional tooth-shaped retro-reflector was designed and manufactured, the light would be returned along the original direction, and the other dimensional direction would observe the principle of specular reflection. The receiving system was placed near the vertical point of the emission point in order to collect most of the reflected light. The problem of the current reflector was solved, that is to say, reflection characteristic disappeared, because the refractive index of the water was different from the air. The experiment adopted a laser with a wavelength of (532±5) nm, power stability <1%, optical noise <0.5%. After it was collimated, the laser was coupled to a single-mode fiber with a length of 2 m, then was widened to a 60° fan sharp laser screen by a Powell lens. The beam expander module used nylon as the waterproof material, and the receiving optical fiber was uniformly distributed around the light source to form an annular fiber bundle, and the other end of the optical fiber was evenly arranged and directly coupled with the PIN photodiode. In front of the photodiode, a center wavelength 532 nm optical filter was added, FWHM = (3±1) nm and the transmittance was 70%. The effective size of the PIN photodiode was 5.0 mm×5.0 mm. Adopted multiple adjustable optical signal conditioning circuits to adapt to different sizes of targets. The system performed different velocity of targets measurement. The steel file was used as a launching device. The signal was collected through fiber; then processed by conditioning circuit, finally, transmitted to the computer. The waveform and the average velocity were obtained. The distance between the two laser screens was a constant value of 300 mm, and the peak value of the waveform was used as a timing moment. The higher SNR waveform signals were acquired successfully. That system has been tested for different target speed parameters, and the waveform signal and the target speed value of higher signal-to-noise ratio have been successfully obtained. The experiments of different target were set up, and the signal waveform with high signal-to-noise ratio was successfully obtained. The absolute error was obtained by comparing the underwater moving target model with the simulation results. The experimental results showed that the proposed method can achieve the test requirements of 1 m×1 m in effective area, the minimum measurable target size of 5 mm. The accuracy of system was more than 0.2%, though compared with the results of initial velocity measurement and empirical formula.
刘 吉，武锦辉，于丽霞，张 静，杨 琦. 分体式原向反射法水下武器速度测试技术研究[J]. 光谱学与光谱分析, 2019, 39(01): 26-30.
LIU Ji, WU Jin-hui, YU Li-xia, ZHANG Jing, YANG Qi. A Split-Type Reflective Method to Measure the Velocity of the Underwater Weapon. SPECTROSCOPY AND SPECTRAL ANALYSIS, 2019, 39(01): 26-30.
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