Radiation Performance Simulation And Analysis Of GF-4 Geostationary Satellite

With the launch and preliminary application of the GF-4 geosynchronous satellite,its advantages of taking into account the high space and high temporal resolution are unique in the same type of satellites.The research on geostationary satellite imagery in China has also received increasing attention.In order to evaluate on-orbit detection capabilities of the high-resolution satellite GF-4 and to grasp the available image data period during the day to rationally schedule the start-up time to improve the satellite use efficiency and extend the lifespan,it is necessary to provide typical features represented by dark pixels(such as water bodies).Conduct radiated energy simulation and SNR research.Based on given spectral capabilities,geometrical and atmospheric parameters,and in combination with land surface properties(Hong Kong coastal water),The GF-4 sensor hyperspectral remote sensing in standard atmospheric conditions including Pan wave band and the blue,green,red and NIR-four wave bands have been simulated using the radiative transmission model MODTRAN.On this basis,interference of atmospheric path radiance was removed to calculate the effective SNR.The data of four typical time nodes in spring equinox,summer solstice,autumn equinox and winter solstice were selected for analysis.In this way,one obtains realistically simulated hyperspectral top-of-atmosphere apparent radiance,ground effective radiance and path radiance,identifying the effective time that the satellite can obtain high quality water image in the observation of the same day,especially analyzing the sensitivity of the critical weak signal during the dawn-dusk period.This work fills the gaps in the data quality assessment,having a positive significance of the scientific and rational use of GF-4.The results show that the highest apparent radiance of summer solstice and winter solstice are successively:59.26 56.20 W/(m2·sr·?m),all in the blue band;the highest ground effective radiance of summer solstice and winter solstice are 17.52 and 12.13 W/(m2·sr·?m),respectively,also in the blue band.The highest effective SNR of the summer solstice and winter solstice are 41.0 and 38.2 dB respectively,the simulation results of blue band is the worst,yet NIR,green and Pan bands are well.To ensure the image quality,set the water effective SNR of 35 dB as a threshold value to determine the boot time.The time of image acquisition is 7:49-17:01 in summer solstice,9:2&-15:07 in winter solstice.In addition,the influence of the changes in water vapor and aerosol optical thickness on the simulated radiance was analyzed.Through simulation,it is found that the influence of water vapor uncertainty on the radiance of satellite observations is very weak.In general,the water vapor changes within 20%,and the radiance does not change by more than 1%.This is because the high-resolution No.4 band setting avoids the strong absorption of water vapor.Band.For comparison,in the polluted weather with very low visibility,the apparent radiance does not change much,and the increment shows an increasing pattern of "M" over time,ie,at 7:00-8:00 am and in the afternoon at Beijing time.The increase from 16:00 to 17:00 in Beijing time was obvious,and there was little change at noon.The radiation increases significantly and the effective radiation at the surface is significantly weakened.The effective radiation values of the midday time series for the four typical seasonal intraday equinoxes,summer solstice,autumnal equinox,and winter solstice all produced attenuation of 20%to 40%,among which the winter solstice blue light band was the most obvious,reaching 38.15%.During the on-track operation of GF-4 on July 26,2017,from Taihu Lake area from 08:30 to 18:01 Beijing time,continuous intensive observations were made,resulting in a total of 41 scene images,forming a time series of observations of the Taihu Lake research area.image.This article will preprocess and screen high-resolution number 4 time-series images as a reference for analog accuracy evaluation(Note:There are also differences between the image values and the radiance at the true entrance pupil of the satellite).At the same time,by constructing a radiative transfer scenario,the satellite observations at Taihu Lake on July 26,2017 were simulated under time series in the standard atmosphere,and the time-series simulations under the synchronized atmosphere optimized for observations on the day of the Taihu Lake photometer CE318 simultaneously.On this basis,using the actual image time series as a reference,the above two sets of time series values were compared and evaluated.The study found that the use of ground-based synchronized surface aerosol data for simulation can improve simulation accuracy.The Root Mean Square Error(RMSE)and the Mean Absolute Error(MAE)can be used to reflect the error between analog and satellite image values.By comparison,in addition to the blue light,green light,and other full-color,red light,and near-infrared wavebands,the analog values of the synchronous aerosol optical thickness are all superior to the standard atmosphere.To a certain extent,the above results also show from the side that the satellite blue and green wavelength bands have large errors.This conclusion is consistent with previous experience and simulation results of this paper.