Research On Brdf Detector Of Space-based Space Target Observing System

Excellent stray light suppression capability is the basis of normal operation of space-based space object observation system.At present,the stray light suppression ability of the system is usually accomplished by analysis software.In which the bidirectional reflection distribution function(BRDF)of the material surface play an indispensable role.The BRDF data used in the analysis process are mostly BRDF fitting models,which are different from the BRDF of the actual material su rface.Stray light analysis results and real results will be inevitably quite different,so it is very important to obtain real and complete BRDF data of material surface.Based on this,the paper built a set of BRDF testing device.This paper not only introduces the source and classification of stray light in space-based space target observation system,but also the principle of hood suppressing stray light and the commonly used methods of stray light analysis.Combining the surface radiation transfer equation with the definition of BRDF,the mathematical model of BRDF in stray light analysis of hood is established.The theory of BRDF is described in detail,and its ability to describe the light scattering properties of materials is clarified.Through the analysis of the theoretical part,it can be fully understood that the analysis of stray light is inextricably linked with BRDF,whether it is inside the system or hood.Therefore,the BRDF measurement of the material surface of space-based space object observation system is very important for the analysis of stray light.In order to solve the problem that the principle of relative measurement is widely used in BRDF testing,an absolute BRDF testing device is built in this paper.The results of absolute measurement are similar to those of relative measurement.The device uses a aperture,a collimator beam expander,and a focusing lens to modulate the laser beam to obtain a relatively uniform circular spot and limit the solid angle of the beam;the photomultiplier tube is used as a detector,and the lock-in amplifier is used to achieve system noise suppression and improve the accuracy of the test results;carrying the light source and the target with a high-precision rotating table to achieve angular positioning,with high angular resolution and repeated positioning accuracy,through the actual test,the system repeatability is better.The system can not only test the BRDF of opaque material surface,but also the bidirectional transmission distribution function(BTDF)of translucent surface.The BRDF and BTDF of Polymethylmethacrylate(PMMA)materials are tested by this device.The light scattering characteristics of PMMA materials can be preliminarily understood by the test results.The BRDF and BTDF of PMMA are tested by the device.The light scattering characteristics of PMMA are preliminarily understood through the test results,which can provide some reference for the design of the hood.