KEYWORDS: Antennas, Solar radiation, Signal attenuation, Fiber lasers, Reflectors, Stray light, Solar energy, Light absorption, Transmittance, Radio telescopes
When the large-aperture antenna pose is measured by the laser method, the subreflector has a strong energy due to the convergence of the antenna itself and the instability of the near-ground atmosphere, and then the laser signal is easily drowned out. Atmospheric attenuation and other factors will weaken the laser transmission in different spectral bands, which reduces the recognition accuracy of laser spots. Aiming at the research of measuring the laser spectrum of large-aperture antenna, this paper analyzes the influence of atmospheric attenuation on the signals of different laser spectrum bands under the fixed distance of subreflector measurement, and compares the solar radiation energy of different wavelengths in laser. Finally, the stray light simulation analysis and experiments are carried out on different laser working spectrum bands to verify the accuracy of the spectrum research used in antenna measurement. Experiments show that the 1064nm wavelength spectrum, as the working spectral band of the antenna measurement, the spot information is more obvious, which can effectively realize the extraction and identification of the spot center and provide a strong guarantee for the antenna pose measurement.
With the increasingly widespread and important application of optics in modern human life and production, research on the propagation characteristics and correction methods of light beams in the atmosphere near the ground surface is becoming increasingly important. The complex atmospheric environment near the ground can affect the propagation of light beams, causing effects such as energy attenuation, beam expansion, beam drift, intensity flicker, phase fluctuations, etc., reducing the quality of beam propagation and affecting the performance of optical applications in various fields. A review was conducted on the impact of near-Earth atmosphere on beam propagation and its correction methods, mainly elaborating on the effects of atmospheric absorption, scattering, and turbulence on beam propagation. Correction methods such as adaptive optics, large aperture receiving, spatial diversity, partially coherent light propagation, and image processing are proposed.
Laser measurement technology is widely used in antenna main reflector and subreflector deformation or pose measurement. Based on the laser measurement technology, atmospheric turbulence caused by the atmospheric characteristics or the convergence effect of the antenna itself will affect the refractive index disturbance during laser propagation, which affects the accuracy of the laser measurement of the antenna deformation or pose. In order to solve the problem of laser atmospheric propagation deflection caused by atmospheric turbulence on the near-ground of a large-aperture antenna, firstly, this paper decomposes the laser atmospheric propagation path into multiple isotropic air layers, calculates the atmospheric refractive index of each air layer, obtains the atmospheric refractive index of the whole laser propagation path through curve fitting methods, and then assesses the laser deflection. Secondly, the turbulence intensity under sunny daytime and cloudy nighttime are evaluated, the laser spot position deviation is compared and analyzed, and the matching relationship among turbulence intensity, theoretical deviation of the laser spots, and actual spot deviation is obtained. Finally, the deflection of laser atmospheric propagation is fitted and calculated by measuring environmental data matched to the actual experimental data of the Nanshan 26m radio telescope antenna, which verifies the effectiveness and feasibility of the proposed method.
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