Study On Statistic Filtering For High-precision Absolute Distance Measurement Based On Femtosecond Lasers

Distance measurement is a traditional kind of measurement work but of great significance.Measurement precision and update rate become important index in the field of control positioning or tracking measurement,such as satellite formation flight,precision machinery,large-scale manufacturing and so on.Femtosecond laser ranging system has advantages in high accuracy,large range,and high update rate,which is very suitable for the above applications.However,the effect of white Gaussian noises during the measurement will result in the decrease of measurement precision.An absolute distance measurement system based on dual femtosecond fiber lasers is established in this paper.Meanwhile,a method based on Kalman filter technique is proposed to improve the absolute distance measurement precision on the basis of high update rate and high measurement accuracy of the ranging system.The main contents of this paper include the following parts:1.Several methods of absolute distance measurement are compared.The research history and present research results of absolute distance measurement based on femtosecond laser were reviewed.The measurement principle and the absolute distance measurement system based on dual femtosecond fiber lasers are introduced.The basic principle of the time-of-flight optical equivalent sampling method based on two femtosecond lasers is analyzed by introducing the optical asynchronous sampling principle.In addition,the measurement devices in the system and method of data processing and absolute distance calculation steps are introduced.2.Theoretically,several kinds of statistical filtering methods and their filtering effects of the simulation distance measurement results are compared including time domain solution and frequency domain solution of Wiener filtering and SSM.Discrete Kalman filtering method which can guarantee the measurement update rate is selected to reduce the random noise of the absolute distance measurement system.The threedimensional Kalman state space model of the filtering system is proposed and an improved Kalman filter algorithm based on femtosecond laser ranging system is proposed,including distinguishing and rejecting outliers,the adaptive filtering method of Q matrix and the adaptive filtering method of R matrix.3.Experimentally,a distance measurement system based on dual femtosecond fiber lasers is established and the dynamic performance of the absolute distance measurement using discrete Kalman filter method is tested.When the target is in a statistic state,the experimental results show that the standard deviation of the distance measurement is reduced by an order of magnitude by using Kalman filtering technique.Meanwhile,the accuracy and precision of the Kalman filtering results are tested in the indoor large scale standard device of the National Institute of Metrology.When the target is moving,optimal estimated speed value can be also output.The standard deviation of the estimated speed is about 4 ?m/s when the target is moving at a uniform speed.The filtering results can follow the distance measurement results very well and significantly improve the measurement precision for sinusoidal vibration.