Research On Synchronous Measurement Of Multi-Angle Scattered Light Field Based On Panoramic Imaging

Multi-angle Scattered Light Field(MASLF)is the energy distribution of scattered light from multiple angles in the hemispherical space of the target object,which can finely characterize the scattering characteristics and intrinsic properties of the object,and has broad application prospects in basic and prospective research fields such as optics,aerospace remote sensing,and computer graphics.The measurement instrument for scattered light field can be divided into traditional measurement instrument based on mechanical structures and fast measurement instrument based on optical technology.Traditional measurement instrument has formed a mature commercial equipment with high accuracy,but the low measurement efficiency is a barrier that is difficult to break through,while the measurement for a long time makes it difficult to obtain the scattered light distribution of the objects in variable environments.Fast measurement instrument based on optical imaging technology can acquire scattered light signals from multiple angles simultaneously within one exposure time of the detector,providing high measurement efficiency.However,the fast measurement instrument is limited by the performance of the light field acquisition optical system on the one hand,and the angular resolution of the fast measurement for scattered light over a wide range is not clear,making it difficult to achieve high precision measurement of the scattered light field from multiple angles of the target object.On the other hand,the fast measurement instrument using optical devices to collect the scattered light field information in a wide range of hemispheric space synchronously,due to the unique optical properties of the optical devices,different forms of noise will be introduced into the measurement system,reducing the signal-to-noise ratio of the measurement results.In view of the existing problems of scattered light field measurement,this thesis proposes a MASLF synchronous measurement method based on PI technology to achieve the synchronous measurement of multi-angle scattered light field of target objects with different characteristics,and verifies the effectiveness of MASLF synchronous measurement method through simulation analysis and experiments.The main studies are as follows,(1)To realize "snapshot" measurement of multi-angle scattered light field,by comparing and analyzing the principles of absolute and relative measurement of scattered light,by means of the advantages of high accuracy and unrestricted range of absolute measurement,and the characteristics of fast measurement by using different types of special optical surfaces to achieve,the theoretical model of synchronous absolute measurement of multi-angle scattered light field based on panoramic imaging technology is studied,a MASLF synchronous measurement method is proposed,and the measurement scheme including the measurement optical system,angle mapping function and noise cancellation technology is clarified to provide the theoretical basis for the subsequent research work of the thesis;(2)In response to the problem that the angular resolution of the fast measurement form based on imaging technology is not clear,resulting in low accuracy of the measurement of scattered light in a wide range,according to the principle of the catadioptric panoramic imaging and the single viewpoint model,the compositions of the measurement optical system and target parameters are analyzed,and an off-axis catadioptric panoramic imaging optical system is designed and improved.In the 380-780 nm spectral range,the optical system can achieve full perimetric azimuth,zenith angle 0 ～ 80 ° field of view hemispheric light field light collection,and in the full perimetric azimuth,zenith angle 2 ° ～ 80 °,can achieve multi-angle scattered light field zenith direction measurement angle resolution 1 °,azimuth direction measurement angle resolution 10 °,respectively;(3)To solve the problem that hemispherical dome scattering generates noise during multi-angle scattered light collection,resulting in low signal-to-noise ratio of measurement results,a MASLF synchronous measurement calibration method is proposed.Based on the ray tracing model of the measurement optical system,the angle mapping function adapted to the measurement optical system is established to form the correspondence between the measured value of the multi-angle scattered light field and the spatial angle of the scattered light.By analyzing the scattering characteristics and noise suppression mechanism of the hemispherical dome,a dome noise cancellation algorithm is studied using the light field transmission matrix to improve the signal-to-noise ratio of multi-angle scattered light measurement results.Through simulation analysis,for the region with a strong light field signal,the effect brought by scattered light noise is approximately 0.3%-0.8%,for the region with a relatively strong light field signal,the effect brought about by scattered light noise is approximately 1.6%-3.3%,and the calibration method can extract the weak scattered light signal that drowned in the noise;(4)The MASLF synchronous test system was designed and built,and the performance of the test system was verified by using standard white boards with different reflectance.The test error in the full field of view range was less than 15%,and the extended uncertainty of the test system was 5.59%.The scattered light field of reflective mirror and opacified glass with typical optical properties was measured and analyzed by the MASLF synchronous test system,and the measurement results were consistent with the theoretical results.In summary,in order to realize the synchronous measurement of multi-angle scattered light field,this thesis proposes a multi-angle scattered light field synchronous measurement method based on panoramic imaging,clarifies the angular resolution in the form of fast scattered light measurement by designing an improved off-axis refractive panoramic measurement optical system,improves the signal-to-noise ratio of scattered light field measurement results based on the noise cancellation algorithm of dome scattering characteristics,verifies the feasibility and reliability of the multi-angle scattered light field synchronous measurement method proposed in this thesis by combining simulation analysis and experimental results,and provides a theoretical research basis for the development of fast scattered light measurement technology.