Research On Cross Calibration Of GF1 Satellite Time Series Based On Stable Target Field

Radiation calibration is the premise of quantitative remote sensing,and its accuracy directly affects the reliability and accuracy of quantitative application of remote sensing data.The researchers have proposed a variety of on-orbit radiation calibration methods,including on-board calibration,site calibration,cross calibration,and scene calibration,where the accuracy of cross calibration can be close to alternative calibration methods,with higher calibration frequency and lower calibration costs can also be used for historical images.At the same time,the ideal radiation calibration field is the basis for achieving on-orbit radiation calibration.At present,China mainly uses the Dunhuang National Radiation Calibration Field for on-orbit radiation calibration.However,the Dunhuang National Radiation Calibration Field has a single feature type and surface damage.Increasingly serious and other shortcomings,there is an urgent need to select and evaluate new calibration sites.The GF1 satellite is mainly based on site calibration,with less frequency of calibration,lack of time series studies of satellite sensors,insufficient understanding of satellite sensor attenuation,and lack of mutual verification of multi-site calibration results.In view of the above,by analyzing the site selection requirements of the calibration site,the four stable target sites of Dunhuang National Field,Dunhuang New Field,Dazhaohuo East and Dazhaohuo West were determined,and the surface and atmospheric characteristics of the site were evaluated.Using Landsat8 OLI as the reference sensor and GF1 WFV as the sensor to be calibrated,the long-term image data from 2013 to 2019 was acquired.Using IDL programming language,cross-calibrate the determined image pairs to obtain the time-series calibration results,construct the attenuation model of the satellite sensor,and verify the accuracy with the site calibration results of China Centre for Resources Satellite Data and Application.The main research conclusions are as follows:(1)Using high-resolution satellite panchromatic images,Landsat8 multi-spectral images,site measured spectra,MODIS images,MODIS water vapor products and historical weather,the uniformity,stability,spectral characteristics,directional characteristics,water vapor content and number of sunny days of Dunhuang National Field,Dunhuang New Field,Dazhaohuo East and Dazhaohuo West were compared.The results show that the three newly selected sites meet the requirements of the radiation calibration field and are suitable for the on-orbit radiation calibration of satellite sensors.This provides a reference for the selection and evaluation of future calibration sites.(2)The Landsat8 OLI with high calibration accuracy is selected as the reference sensor to cross-calibrate the GF1 WFV sensor.The results show that the relative difference of the time series cross-calibration coefficients of different sensors in different calibration sites does not exceed 4.91%,3.87%,3.78%,4.31%,and the standard deviations are less than 0.01.The four radiation calibration sites have good consistency,the time series calibration method has good stability,and the calibration results have good reliability.(3)According to the time series cross-calibration results,the satellite sensor attenuation model formula is fitted,the initial calibration coefficient and the annual attenuation rate are determined,and analyzed and verified with the site calibration results of China Centre for Resources Satellite Data and Application.The results show that the initial calibration coefficients of the satellite sensors obtained in different calibration fields are relatively close,and the relative difference is between 3%-7%,that is,the calibration results of different sites have good consistency.The annual attenuation rate of each satellite sensor does not exceed 0.20%,0.11%,0.28%,0.35%,that is,each sensor of GF1 satellite has not experienced significant attenuation in the past 7 years.In each sensor,a total of 40 years of site calibration coefficients are within the cross-calibration coefficient threshold,72 years of site calibration coefficients exceed the cross-calibration coefficient threshold,the minimum is 2.91% from the threshold center,and the maximum is from the threshold center 29.71%.