Research On Radiation Calibration Method And System Of Satellite Remote Sensing Point Light Source

Satellite remote sensing has been widely used in many domains,such as the national economy,social life and national security.Its application efficiency greatly depends on the quantitative quality of the available remote sensing data.On-orbit modulation transfer function(MTF)detection and radiation calibration for satellite remote sensing are the basis of satellite remote sensing quantification.Vicarious calibration with a site as the observation target is one of the three main methods of satellite calibration.It has the technical advantages of high-precision detection and calibration for the entire life cycle of on-orbit satellites.Vicarious calibration mainly takes a large-area uniform field,artificial target or point light source as the reference target.Because large-area uniform fields in the natural environment are relatively remote and artificial targets have problems such as laborious setup and susceptibility to surface aging,it is difficult to use them as high-frequency,routine long-term calibration reference targets.The point light source method relies on a group of convex mirrors and has potential advantages for overcoming the above shortcomings.It has important application prospects in future satellite on-orbit calibration.A point light source is composed of convex mirrors,and its pointing accuracy is determined by the diameter and weight of the convex mirrors.The network remote control of point light source pointing is the basis of any calibration routine.Therefore,the most commonly encountered problems in point source calibration and MTF detection are mainly related to pointing accuracy and network control.In this work,research on the development of networked remote control systems for point light sources and a method for high-precision pointing calibration are carried out.According to the characteristics of the multilevel gradient array of the point light source and the requirements of high-frequency routine calibration,a concept of pointing and tracking based on networked remote control and a high-precision point light source array is proposed,and the software and hardware schemes of the corresponding point light source radiation calibration system are designed.A set of on-site vicarious calibration point light source systems has been developed to enable automatic tracking and networked collaborative work.This set of systems has a universal applicability function that can be used as a reference target for on-orbit radiation calibration and MTF detection under conditions of different latitudes,different seasons,and different satellite resolutions.Regarding the point light source systems facing the camera,the point light source,earth and sun units are all independent of each other but should have high-precision pointing application requirements.Based on the sun vector,an algorithm for converting any vector in the mirror coordinate system into the local coordinate system through a coordinate transformation relationship has been developed to ensure the integrity of the coordinate system.On this basis,a high-precision calibration model has been constructed,and this model has been verified and improved through the inverse model solution method,the sun image centroid comparison method,and the coordinate rotation transformation matrix method.This calibration model endows the developed point light source calibration system with high-precision pointing ability in the local coordinate system.On the basis of realizing high-precision calibration capabilities for point light source systems in order to achieve high-frequency regularization and automatic applicability based on point light source MTF detection and calibration,this paper further proposes the idea of adding an automatic camera to the point light source system and presents an automatic calibration model study carried out based on the geometric relationship between the mirror and the camera so as to determine the quantitative relationship between the centroid of the sun image and the normal direction of the mirror.Through experiments,the high-precision automatic adjustment ability of the system pointing to the sun has been verified and perfected.Based on the development of the presented point light source radiation calibration system,the high-precision calibration of point light source systems and research on calibration process automation,a series of point light source pointing experiments were also carried out.The comparison between the model analysis and a sun tracking experiment shows that the standard deviations of the pitch angle and azimuth angle errors are 0.017° and 0.031°,respectively.The root mean square errors of the image centroid contrast are 2.099 and 0.868 pixels along the X-and Y-axes,respectively.The corresponding pixel angular resolution errors are 0.037°and 0.014°,and the comprehensive angle resolution error is 0.040°.The experiments show that the values calculated using the model are in good agreement with the actual measurement data,satisfying the requirements for MTF detection and radiation calibration based on point light source systems.