The Research Of On-orbit Radiometric Radiance Calibration Method And Quantitative Application Verification For Nighttime Sensor Of LuoJia1-01 Satellite

The nighttime light(NTL)remote sensing satellites have the capability to detect faint sources emitted on the Earth's surface,this ability allows for the capturing NTL signals emitted by artificial lights,building,roads,infrastructure,and fishing boats on the Earth's surface,and providing a great opportunity to understand the magnitude and changes of humanity's activities.The past decades,the NTL data mainly comes from the DMSP-OLS and NPP-VIIRS,the successful launch of Luojia1-01 NTL remote sensing satellite has enriched the data source of NTL application.The products quantitative applications require high precision calibration process.The laboratory calibration had calibrated the stray light,linearity,and dynamics of the sensor to a certain extent by using a uniform light before launching,after the satellite entry into orbit,the sensor is affected by space environment(such as temperature and radiation),causing degradation and the change of the radiometric response of the devices with time.Therefore,on-orbit calibration must be carried out to ensure the radiometric quality of the image.Owing to the lack of on-board calibration equipment and the absolute radiometric calibration light source at night,it is difficult for LuoJia1-01 to carry out on-board calibration equipment assisted calibration.On-orbit calibration method is time-consuming and labor-consuming,and the measurement is easily affected by the atmosphere,resulting in low calibration frequency.The accuracy of cross calibration is limited by the reference sensor.The moon,as an exoatmospheric stable radiation source,the surface's radiation characteristics can be quantified by an irradiance model,which is often used as the reference for on-orbit calibration and stability monitoring of remote sensing sensors.In this study,based on the continuous lunar observation of Luojia1-01,the on-orbit radiometric calibration was implemented by using the ROLO lunar irradiance model,and the response stability was monitored nearly one year after launch.The performance differences of the NTL data before and after radiance calibration in predicting PM_2.5 concentration were compared to evaluate the impact of radiance calibration on the quantitative application.This paper has analyzed existing absolute radiometric calibration method,and combined the characteristics of the LuoJia1-01 satellite to formulate a high-efficiency and low-cost radiometric calibration plan based on the observation of the moon,the calibration accuracy and response stability was also analyzed.Furthermore,the effect of absolute radiometric calibration for image quantitative applications was also assessed,the specific contents and results are as follows:(1)Research on the relative radiometric calibration of LuoJia1-01 satellite sensorsAfter analyzing the imaging radiometric error source,the relative radiometric calibration model,the benchmark,the difference of calibration parameters,as well as the design and imaging characteristics of the LuoJia1-01 remote sensing satellite sensors.This study selected the dark current calibration method and uniform field calibration method to correct the relative response differences of different detectors of Luojia1-01,eliminating systematic errors such as stripes in the original image.The relative standard deviation after the on-orbit dark current calibration is better than 0.05DN and 0.07 DN of the high and low gain data,respectively.The dark current response difference of all detectors with the high and low gain is effectively corrected,and some highlight pixels of the detector response are removed.After calibration of the on-orbit uniform calibration sites,the maximum strip ccoefficients of the daytime images are0.17%and 0.18%,respectively,and the response inconsistency of the sensor is effectively corrected.(2)Absolute radiometric calibration based on the observation of the moonOwing to the lack of on-board calibration equipment and the absolute radiometric calibration light source at night,it is difficult for LuoJia1-01 to carry out on-orbit radiance calibration.In response to this question,we analyzed the advantages and disadvantages of different calibration methods,the characteristics of moon.The on-orbit radiance calibration of LuoJia1-01 is realized by using the observed lunar images.The ROLO model,which takes into account the effects of lunar phase Angle,libration,geometric distance,and the positive and negative phase angles,is used to calculate the observed irradiance of the moon during imaging,after distance correction and spectral matching,the radiance is obtained.The integrated"DN"value of the moon disk can be obtained by range recognition and edge fitting of the satellite observation image.Once the lunar radiance and the lunar disk DN are known,the radiance calibration model could be solved to obtain the radiance conversion coefficients of LuoJia1-01 to calibrate the sensor.Comparing the consistency between the calibration results of the model and the laboratory,the calibration accuracy can be obtained.At the same time,the consistency between the irradiance calculated by the model and the image are used to track the changes of the sensor's on-orbit radiometric response.The results showed that:the consistency of the radiometric calibration results based on the ROLO model and the laboratory calibration of LuoJia1-01 exceeded 90%;the nighttime sensor of LuoJia1-01 radiometric response underwent approximately 6%degradation during the observation period of nearly one year(353 days).(3)Quantitative verification of radiance calibration effectAir quality degradations caused by PM_2.5 can lead to various health problems,and accurate PM_2.5 concentration assessment is critical for managing the environment and safeguarding the health of residents.Radiation signals collected by NTL remote sensing satellites are influenced by PM_2.5 concentrations,and thus,incorporating NTL imagery in statistical models has been widely used to predict PM_2.5 concentrations.The new generation LuoJia1-01 NTL data greatly improves the quality of NTL application(high spatial resolution and a broad radiometric quantization range).Therefore,in the last part of this study,the performance difference of LuoJia1-01 NTL data before and after radiance calibration to predict PM_2.5 concentration was verified.The results clearly show that LuoJia1-01 NTL data after radiance calibration can estimate PM_2.5concentration better than those before radiance calibration.In addition,the seasonal PM_2.5 concentrations in Beijing-Tianjin-Hebei from June 2018 to May 2019 were predicted by using the calibrated NTL data,and its spatial and temporal distribution characteristics were evaluated.The results show that the estimation accuracy of AOD-PM_2.5 with LuoJia1-01 as the auxiliary variable is significantly better than that with NPP-VIIRS DNB data.