Design of Frequency Scanning Interferometry Laser Ranging System
Objective The Fengyun-4 microwave detection satellite,positioned in a geostationary orbit,undergoes thermal deformation of its microwave antenna due to solar heat radiation.This deformation compromises the antenna's surface accuracy,consequently affecting the performance of payloads like the microwave imager.To achieve adaptive adjustment of the microwave antenna for optimal payload operation,a real-time,high-precision measurement system and method for the antenna surface are essential.The frequency scanning interferometry(FSI)laser ranging system,also known as the frequency modulated continuous wave(FMCW)laser ranging system,offers high-precision absolute distance measurements for non-cooperative targets at short to medium ranges.It exhibits robust interference resistance,making it suitable for on-orbit surface measurement of satellite antennas.Despite existing research and commercial products,the demanding on-orbit environment necessitates advanced FSI laser ranging system designs.We introduce a system design that integrates miniaturization,modularity,and high reliability into the FSI laser ranging system,making it suitable for spacecraft deployment.This system meets the antenna surface measurement needs of the Fengyun-4 microwave detection satellite for both on-orbit and terrestrial applications.It also shows potential for broader automotive,aerospace manufacturing,and large-scale equipment production.Methods A mathematical and physical model of a typical FSI laser ranging system(Fig.1)is developed based on the light interference formula.This model facilitates the derivation of distance measurement principles and calculation formulas under ideal conditions.Further,the nonlinear error in laser frequency sweeping is analyzed,with the simulation results shown in Fig.2.An enhancement to the standard FSI ranging system is proposed,incorporating a reference optical path(Fig.3).This path provides a reference beat frequency signal for resampling the measurement signal at equal optical frequency intervals,thereby eliminating measurement errors caused by nonlinearities in laser frequency sweeping.Analysis of Doppler frequency shift errors was conducted through formulaic analysis,with corresponding simulation results presented in Fig.4.The paper proceeds with a design scheme for an FSI laser ranging system featuring dual-laser synchronized reverse modulation and symmetrical optical paths(Fig.5).Utilizing the established mathematical and physical model,formulaic derivations are conducted methods to correct Doppler frequency shift errors are outlined,and simulation analysis results are shown in Fig.6.Additionally,an analysis of system measurement errors induced by environmental factors such as temperature fluctuations and vibrations in optical fibers is performed,followed by specific countermeasure suggestions.Subsequently,based on the design proposals from Sections 2.3 and 2.4,a modular FSI laser ranging system is conceptualized(Fig.7),and an engineering prototype is assembled for ranging experiments(Fig.8).The target is placed on a high-precision displacement platform 2.5 m away,and continuously move the target within a±5 mm range with a step size of 500 μm.The calibrated FSI ranging system engineering prototype is utilized to measure the target and perform error correction and analysis on the measurement results.Results and Discussions We present a mathematical and physical model to analyze the principles and errors associated with the FSI laser ranging system.The research addresses and reduces errors from laser frequency sweeping nonlinear and Doppler frequency shift.The proposed design integrates an internally modulated laser source with an all-fiber optic path and passive optical components,enhancing system reliability and modularity.An experimental prototype developed following this design demonstrated high precision in measuring distances to a target approximately 2.5 m away.Subsequent calibration and correction for Doppler frequency shift errors,as depicted in Fig.9 and Fig.10,reduced repeatability standard deviation from 271.5 μm and 270.26 μm to 15.32 μm and decreased the system measurement linearity error to 16.92 μm.These findings indicate that the system design fulfills the antenna surface measurement requirements for the Fengyun-4 microwave detection satellite in both on-orbit and ground-based applications.Conclusions The FSI laser ranging system design utilizes equidistant optical frequency,resampling,dual-laser synchronized reverse modulation,and dual-path symmetrical interferometric measurements.It eliminates errors introduced by laser frequency nonlinearities and corrects Doppler frequency shift errors caused by various factors.The engineering prototype,built based on the proposed system design,demonstrated precise measurements for a target approximately 2.5 m away,with measurement linearity superior to 2.14×10-6 and a repeat measurement standard deviation better than 17.00 μm.The all-fiber optic and passive device internal optical path allows for a fully solid-state,compact,and modular design,meeting the high-reliability requirements of the system.It also effectively reduces measurement errors caused by air disturbances and mechanical vibrations,making it suitable for real-time high-precision measurement applications of satellite antenna surfaces in space and on the ground.
frequency scanning interferometrylaser rangingequidistant optical frequency samplingDoppler frequency shiftFengyun-4
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