| Due to being constrained by bad weather,budget,personnel availability,travel time to test-site,and so on,the calibration frequency of the manual field campaigns for radiometric calibration is limited.With the sharp increase in satellite numbers and species and the comprehensive application of multi-platform remote sensing data,traditional calibration approach has been difficulty to meet the needs of current remote sensing applications.In order to realize the improvement of calibration frequency for satellite remote sensors while keep the current calibration accuracy,the technical process for automated radiometric calibration in test-site(ARCT)and the hardware and software platform are established,while a radiometric calibration experiment for MODerate-resolution Imaging Spectroradiometer(MODIS)is carried out in this paper.The works in this dissertation are mainly focused on the following aspects:The basic technical process of the ARCT approach is established.An automated radiometric calibration method is determined based on the variation characteristic of surface reflectance in test-site over time,which is studied by historical remote sensing data.According to the characteristics of surface reflectance curve which only adjust up and down in a small range over time,the real-time hyper-spectral surface reflectance is obtained by translating a reference reflectance curve refer to the multi-spectral surface reflectance monitored by a multi-spectral test-site radiometer.At the same time,the atmospheric parameters are obtained by a solar radiometer.Combined with radiation transmission code,the top-of-atmosphere(TOA)radiance at the entrance of the satellite remote sensor is obtained to realize the radiometric calibration for overpass payload.The field automatic observation equipments,an automated test-site radiometer(ATR)for surface radiance and a precision solar radiometer(PSR)for atmospheric characteristics,are developed.In order to ensure the stability and reliability of observation data,the temperature sensitive devices such as aperture stops,filters and detectors are maintained a stable temperature range.In order to easy access to measurement data,the Beidou short-messege communication is used for wireless and long-distance transmission of measurement data.The radiance calibration for ATR in laboratory is carried out using the "standard lamp +reference pannel" calibration system and the the annual variable rate of calibration coefficient is not more than 2.5%which indicates that the optical performance of ATR is very stable for a long time.Meanwhile,the calibrations for ATR are excuted in test-site utilizing the uniform radiance field on the reference panel formed by sunlight,and the advantage lies in that the spectral shape and amplitude in calibration is close to that in routine,which can avoid introducing the uncertainties from difference in spectral shape.The absolute radiometric calibrations for PSR are performed using the Langley calibration method and the main instrument transfer calibration method and the relative deviation of calibration results is better than 0.9%.The deviation of aerosol optical depth from CE318 and PSR simultaneous observation is not more than 0.02,which indicates that the measurement from PSR has hight precision.An automatic calibration software is programmed,which achieve the automation of the whole link from data acquisition to the radiometric calibration.The hyper-spectral TOA radiance which can realize the radiometric calibration of any remote sensors can be outputted directly according to the measurement data.The ARCT experiments for MODIS are performed.The calibration result shows the average relative deviation between TOA radiance obtained by ARCT and MODIS/Aqua is less than 3.7%and less than 5.2%for MODIS/Terra,which indicates ARCT can maintain the radiometric accuracy on par with manned field campaigns.ARCT for MODIS is continuous carried out for 4 months,10 effictive calibrations,in 2016,and improves the calibration frequency of remote sensors,from current once annual to 2?3 times every month.This paper takes the lead in establishing an automatic calibration system in China,which realize the long-term automatic acquisition of the surface radiance and atmospheric parameters and the long sequence automatic calibration for remote sensors.The result of research shows that ARCT technology is significant for application,which can improve the calibration frequency,reduce the calibration cost,improve the calibration timeliness apparently. |
PDF Full Text Request