基于调制传递函数的激光反射层析成像质量评价方法

Imaging Quality Evaluation Method of Laser Reflective Tomography Based on Modulation Transfer Function

激光反射层析成像技术作为实现空间目标远距离、高精度探测的有效途径之一,其成像质量的优劣对目标的探测精度有着很大的影响。将调制传递函数引入到激光反射层析成像质量评价中,通过求解激光反射层析成像系统的调制传递函数,得到变量为距离分辨率的调制传递函数曲线,在无需先验图像的情况下实现了对激光反射层析成像质量的定量评价,并搭建实验系统进行了验证。实验结果表明,基于调制传递函数曲线得到的距离分辨率与实验系统距离分辨率的理论计算值基本一致,该评价方法能够准确直观地描述激光反射层析成像质量。

Objective With the continuous development of space technology,spaceborne long-distance high-precision detection technology has also made great progress.The imaging resolution is greatly limited because of the influence of the diffraction limit,effective aperture,and other factors of conventional optical imaging technology.Therefore,it is increasingly difficult to meet the needs of high-precision remote detection tasks.As one of the effective ways to realize long-distance and high-precision detection,laser reflective tomography technology has great advantages in the field of long-distance and high-precision detection because its imaging resolution is independent of distance and has high application value in the future.As an important part of the design of a laser reflective tomography system,imaging quality evaluation is of great significance to the application of laser reflective tomography technology.The conventional quality evaluation method of laser reflective tomography usually uses one or more specific values(such as relative root mean square error and image similarity coefficient)as the evaluation standard to realize the quantitative evaluation of the quality of laser reflective tomography.These methods often need a priori image as a reference,and there are large errors and limited scope of application.In this study,we invesitgate a quality evaluation method of laser reflective tomography.This method does not need an a priori image as a reference,and the result is more accurate.We expect that this method and our findings herein can aid the application of laser reflective tomography.Methods We introduce the concept of modulation transfer function into the quality evaluation method of laser reflective tomography and establish the quality evaluation model of laser reflective tomography based on distance resolution.First,the part containing edge information in the reconstructed image is intercepted,and its edge spread function is obtained.Next,the corresponding line spread function is obtained by differentiating the edge spread function.Then,the line spread function is used to obtain the modulation transfer function curve based on spatial frequency by the Fourier transformation.Finally,according to the relationship between spatial frequency and range resolution,the curve is transformed into a modulation transfer function curve based on range resolution to realize the quantitative evaluation of the quality of laser reflective tomography.In addition,we also set up the corresponding laser reflective tomography system and carry out a laser reflective tomography experiment under the detection distance of 0.2 km.The feasibility and accuracy of this method are verified by comparing the experimental results with the simulation results under ideal conditions.Results and Discussions Through the experiment of laser reflective tomography,we get the reconstructed image of the target(Fig.4)and successfully draw the modulation transfer function curve based on distance resolution.In this study,the abscissa value corresponding to MTF value of 10%is considered as the test system’s limit value of distance resolution.According to the obtained modulation transfer function curve based on distance resolution(Fig.7),the corresponding distance resolution at MTF value of 10%is approximately 1.587 cm,which is almost equal to the distance resolution(approximately 1.54 cm)obtained by theoretical calculation.With the increasing abscissa of the curve,the MTF value becomes larger and larger,and the imaging quality becomes better.Compared with the ideal image obtained by simulation(Fig.8),the coincidence degree of their modulation transfer function curves is high,which also reflects the accuracy of the method in this study.In addition,we theoretically analyze the advantages of this method compared with the conventional evaluation methods.On the basis of the results,the modulation transfer function curve based on distance resolution can accurately evaluate the quality of laser reflective tomography.Conclusions We examine a method for evaluating the quality of laser reflective tomography.By introducing the modulation transfer function curve from conventional optical imaging into the quality evaluation of laser reflective tomography,the modulation transfer function curve based on distance resolution is drawn,and a model for evaluating the quality of laser reflective tomography based on the modulation transfer function is established.Quantitative evaluation of the image quality of laser reflective tomography without prior images is achieved.In the experiment,we set up an experimental system of laser reflective tomography and obtain modulation transfer function curves that can characterize the image quality of laser reflective tomography through the reconstructed image of this system,thus verifying this method’s feasibility.By solving the transverse coordinates at MTF value of 10%,the distance resolution of the laser reflective tomography system is 1.587 cm,which is approximately equal to the distance resolution(1.54 cm)of the system calculated by theoretical calculation.Moreover,we compare the experimental results with the simulation results and obtain almost identical modulation transfer function curves,thereby verifying the method’s accuracy.The results demonstrate that the evaluation method of laser reflective tomography based on modulation transfer function can accurately evaluate the quality of laser reflective tomography without prior images.