Calibration Method Of Field Of View Of Sun Radiometer With Limited Step Scanning

Sun radiometer is one of the important ground-based remote sensing instruments to study the aerosol optical characteristics.To qu antify the aerosol's information,having a high accuracy of calibration is the important basis and prerequisite.The field of view(FOV),a key parameter to calibration,plays an important role in transfer calibration and calibration with a integrating sphe re in the laboratory.The paper is focused on the calibration of instrument and its key parameter FOV based on SONET(Sun/sky-radiometer Observation NETwork).This study mainly expounds the calibration method of CE318 which is the standard instrument in SONET and performs expressions deduction for calculating the calibration parameters for each channel of observation,and then analyzes not only the relationship between transfer calibration and FOV,but also the transition between solid view angle and FOV.The normalized contrast result from theoretical and experimental suggests that there is an consistency association between overlapping area of FOV and instrument response.Focusing on the problems that exist in actual measurement,the study does research into the light path structure of CE318.According to the relationship between light path of each component,related parameters were calculated,light path model was built and simulation data was obtained;According to the contrastive analysis of simulation data with scanning measurement data using a laser as light source,we puts forward a new method to compute the FOV combined with experimental measurement data.Based on the above theoretical analysis and simulation,a transfer calibration experiment and a matrix scanning experiment with a 675 nm laser were designed.Through indirect and direct measurement,we obtained the FOV of nearly 20 CE318 instruments.The relative accuracy of FOV was obtained by transfer calibration ranges from 3.86% to 5.78% while that obtained by matrix scanning measurement ranges from 1.29% to 2.02%,which result ranges from 1.25° to 1.31°.In addition,comparing the mean FOV by transfer calibration and matrix scanning measurement of 20 instruments in 2~3 years,we find that the maximum of relative error is less than 2.50%.Thus we conclude that under the condition of having many times transfer calibration in the past,a relative accurate FOV can be obtained by averaging though it has a large error after transfer calibration.At the same time,the result implies that FOV by matrix scanning has a relatively high credibility under the new calculation method.On the whole,three methods all have their own advantages and disadvantages.They can be verified and complement each other,in order to obtain more accurate FOV of instruments.