Research On Internal Stray Radiation Analysis Suppression And Measurement Technology Of Infrared Theodolite

With the development of the measurement and control technology as well as the weaponry,the requirements of detectivity,image quality and radiometric calibration precision are increasing for photoelectric theodolite.Compared with visible systems,infrared systems operate in the way of passive imagery,which means stray radiation can not only result from outside sources,namely the external stray radiation,but also arise from the self-radiation of system,namely the internal stray radiation.To achieve efficient detection of long-distance and weak targets,infrared theodolites typically employ high-precision cryogenic infrared detectors,which are extraordinarily sensitive to thermal sources.In comparison with external stray radiation,the internal stray radiation has a more significant effect on infrared theodolites and has become the bottleneck for performance improvement.In addition,the research on internal stray radiation has been a greater challenge,due to the complexity of outfield conditions.Consequently,the research on internal stray radiation has great significance for improving infrared theodolite performances.On the basis of related literatures,this paper has summarized the research achievements of internal stray radiation at home and abroad,and point out the potential difficulties,which indicates the direction of follow-up research.This paper takes the internal stray radiation of infrared theodolite as the research object,and conducts the research from the aspects of analysis method,suppression measure and measurement method.The main research results are shown as follows:In the aspect of internal stray radiation analysis,the composite irradiance distribution method is adopted to increase the number of traced rays,and effectively solves the problem that the precision of analysis result is restricted by the number of traced rays.The element partition method is applied to internal stray radiation analysis to analyze the influence of element at different positions on internal stray radiation,which can supply reliable analysis result for internal stray radiation suppression.Combined with the composite irradiance distribution method,the internal stray radiation of an infrared system has been analyzed in detail.The validity of the analysis result has been approved by experiments of heating different positions of infrared system.In the aspect of internal stray radiation suppression,the internal stray radiation is comprehensively suppressed from the aspects of thermal sources,transmission path and algorithm compensation.A method is proposed to compensate the temperature drift for infrared theodolites.The effectiveness of the proposed method has been validated by temperature drift compensation experiments at various ambient temperatures.The effect of internal stray radiation drift on system output can be effectively weakened by compensating the output drift and the environmental suitability of infrared theodolite can be improved.The usage of spherical reflective warm shield to suppress internal stray radiation has been analyzed in detail and the analysis model has been built.The detailed theory of spherical reflective warm shield design has been introduced on the basis of the principle that external thermal radiation cannot directly reach the infrared detector.According to the theory developed above,a polished spherical warm shield has been designed to match an F/2 infrared detector with an F/4 infrared system.The simulation result shows that the designed spherical reflective warm shield can suppress stray radiation sufficiently.The contrast radiometric calibration experiments,between the designed spherical warm shield and four flat warm shields with different surface characteristics,have been carried out under normal and different temperature conditions.Experimental results indicate that the detector output caused by the spherical warm shield is less than one-tenth of the output caused by flat warm shields under the same ambient temperature,which illustrates that the spherical reflective warm shield can sufficiently suppress stray radiation and validate the correctness of the proposed design theory.In the aspect of internal stray radiation measurement,the radiometric calibration model considering the integration time and ambient temperature has been established.Three methods have been put forward to achieve the measurement for internal stray radiation of infrared theodolite based on the established model.Experiments have been performed to validate the three proposed methods at various ambient temperature.Experimental results figure that the three proposed methods can achieve high precious measurement of internal stray radiation.Corresponding measurement method can be selected for infrared systems with different apertures and structural styles.It is meaningful to evaluate the suppression performance of internal stray radiation and to estimate the dynamic range and operating distance by measuring the internal stray radiation.