Development And Test Of Site Reflectivity Observation System Based On Direct Method

The traditional site reflectance observation mainly relies on the manual method,and the surface spectrometer is used to measure the surface and diffuse reflection reference plates respectively to obtain the surface reflectance.This method has errors such as time matching,reference board and manual operation.With the increasing number and variety of satellite remote sensors,the current radiation calibration field calibration methods have gradually failed to meet the actual needs of remote sensing in-orbit radiation calibration.In order to develop a new method for measuring the reflectivity of the site and improve the efficiency of the site reflectivity measurement,the high-frequency field substitution calibration of the satellite remote sensor is realized.This paper studies a direct radiation measurement method different from the manual measurement reflectivity method.By directly obtaining the surface reflection radiance and the total irradiance of the sky,the direct surface method is used to obtain the surface reflectance.The method relies on an automated observing system.This paper describes in detail the development and testing of this observing system.The main research work includes the following aspects.The significance and three types of radiation calibration are introduced,and the basic principles of reflectivity-based legal standards are described.The current development status of reflectivity observation equipment and measurement methods at home and abroad is introduced,and the future development trend is analyzed.Aiming at the shortcomings of current reflectivity observation equipment and measurement methods,the technical route of direct measurement of reflectivity is proposed,and the basic principle of the method is expounded.According to the research situation and the principle of the new method,the demand system was analyzed and the overall plan design was carried out.The main automated observation equipment for the observation system was developed:the spectral irradiance meter and the spectral radiance meter for the observation of atmospheric and surface radiation characteristics,respectively,with spectral ranges from 400 nm to 1700 nm.The working principle,overall design,optomechanical system design,electronic system design and PC software design of spectral irradiance meter and spectral radiance meter are introduced.The design of the optomechanical system is described in detail as the main design content of the instrument.According to the characteristics of the observation system,the spectral calibration and radiation calibration schemes were developed.Spectral calibration results show that the spectral resolution of the VNIR spectrum module and the SWIR spectrum module are better than 4 nm and 15 nm,respectively.The system-level radiation calibration was performed on the observation system as a whole.The results of the radiation calibration showed that the uncertainty of the observation system was better than 2.1 8%.The radiation calibration scheme eliminates the uncertainty caused by standard lamps and improves the accuracy of the radiation calibration of the observation system.In order to verify the functional integrity of the observing system and the accuracy of the measured data,the field system was tested in Hefei and Dunhuang respectively.Different experiments were designed and the data was analyzed.An experiment comparing the reflectivity measurement between the observation system and the SVC spectrometer was carried out outside Hefei.The results show that the relative deviation between the reflectance calculated using the laboratory calibration factor and the manual measurement reflectance based on the reference plate is generally less than 2.5%and the maximum is less than 4%;the reflectivity calculated using the self-calibration calibration coefficient is based on The relative deviation of the artificially measured reflectance of the reference plate is generally less than 1.3%and the maximum is no more than 2%.In the Dunhuang Radiation Correction Field,an experiment comparing the reflectivity of the observation system with the SVC spectrometer was also carried out.The results show that the direct method based observation system uses real-time self-calibration calibration coefficient,and the calculated surface reflectivity is compared with the reflectivity obtained by manual measurement based on the reference plate.The relative deviation is generally less than 1%and the maximum is less than 3.%.The experimental data of Hefei and Dunhuang show that the observation system has the measurement accuracy equivalent to the previous manual measurement reflectivity method,and has an effective self-calibration function of calibration coefficient.Because of the advantages of long-term automatic measurement in the field environment,the observation system has broad application prospects for the implementation of fully automatic,high-frequency field substitution calibration for satellite remote sensors.