Modeling and simulation of stray light based on the Visible and InfraRed Radiometer
The effects that stray light has on satellite-borne infrared optical systems are embodied in two perspectives:one is degrading the quality of imaging,and the other is decreasing the precision of calibration.Satellite-borne infrared optical systems are situated in an extraneous atmosphere environment,where stray light is simply formed at a specific operating position relative to celestials such as the sun and the moon.Owing to this,the imaging capability of the payload and the precision of calibration rely vitally on the evaluation of stray light.The Visible and InfraRed Radiometer(VIRR),which embarks on FY-3A/B/C satellites,has been operating in orbit for more than 10 years,during which the massive quantity of data acquired is significant for the study of climate change.The long period of the payload's consistent operation covered various circumstances of illumination.By evaluating the variation of the payload's response in a long time sequence,the changing trend of the payload's on-orbit performance can be obtained,which is of great significance for the recalibration of historical data.The imaging optical system of the VIRR is modeled and simulated by means of TracePro,which yields the Point Source Transmittance(PST)curves of different spectral bands in pitch,scan,and yaw dimension,respectively.PST is one of the widely adopted indicators for the characterization of an optical system's response to stray light.It is defined as the radiance of the detector aroused by an off-axis point source and then normalized to the entrance pupil radiance when the point source is on axis.The experimental stray light measurement of the backup of the on-orbit instrument is conducted as well.Based on the experimental results,a comparative analysis between simulated result and actual measurement is achieved qualitatively.Possible incident angles for which the instrument is susceptible to stray light are found by studying the PST curves.A shield is later mounted on the instrument to demonstrate the effectiveness of the stray light suppression method.To evaluate the on-orbit performance of VIRR under stray light influence,the simulation and analysis of orbital parameters,especially the solar irradiance,are performed as well.Taking into consideration the mutual effects of payloads,the illumination situation during satellite crossing terminator is simulated,and the path through which solar contamination influences the instrument both externally and internally is found.The PST curves of pitch,scan,and yaw dimension of VIRR reveal the geometric profile of the instrument.The peaks of pitch and scan dimension appear at an off-axial angle of 10°,which is consistent with the simulation results.Likewise,there is a peak at a large off-axial angle(～75°)in the pitch dimension,which corresponds to a stray light incident from the motor side.The yaw dimension PST is two to three magnitudes lower than that of the pitch and scan dimension within the range of±20°.This is due to the blockage of the motor housing.Preliminary results of the magnitude of stray light are also obtained.The transmitting path of stray light is predicted by simulation results and later verified by on-orbit data.This work can provide reference for the design of similar payloads with regard to suppressing stray light and preventing sun contamination.In addition,the results yielded can fundamentally support the recalibration of historical remote sensing data.
remote sensingVisible and Infra-Red Radiometer(VIRR)stray light suppressionpoint source transmittance(PST)solar contaminationrecalibration
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