Inversion And Validation Of AVHRR/2 Data In Mid-infrared Reflectance

AVHRR/2 data is of great significance to the study of historical earth surface data.The global monitoring of the properties of objects on the earth's surface mainly depends on the NDVI of AVHRR sensors in red and near infrared bands.The third band of AVHRR,with a central wavelength of 3.75?m,is often used to monitor plants on a regional scale.The separation of reflected energy and emitted energy in mid-infrared band has attracted much attention.Inversion of the reflectivity of the third channel of AVHRR/2 can add a band of reflectivity data for the study of regional climate and ecology.In this paper,based on the theory of radiative transfer,the reflectivity of AVHRR/2 mid-infrared band data in Qinghai-Tibet Plateau is inversed,and the inversion results are verified.Although the method used in this paper has inherent uncertainty,it is proved that it is feasible to quantitatively invert the reflectivity of AVHRR/2 at 3.75 microns.This paper mainly does the following research work:1)according to the radiative transfer process of energy in AVHRR/2 mid-infrared band in the atmosphere,the energy radiative transfer equation is established.Electromagnetic radiation will be absorbed,scattered and reflected when it passes through the atmosphere,and will also be affected by atmospheric emission in the mid-infrared band,but energy is conserved in the whole process,so the equation is established based on the atmospheric radiation transmission process.2)Using MOTRON software to simulate the radiation transmission process of mid-infrared band in the atmosphere,the data of direct solar radiation,atmospheric radiation,atmospheric scattering and atmospheric transmittance were obtained by simulation.Using MODTRAN to simulate the atmospheric radiation transmission process requires setting satellite parameters,atmospheric parameters,surface parameters,etc.By changing the parameter values,different data such as direct solar radiation and atmospheric radiation corresponding to the input parameters will be obtained after running the program.3)The surface temperature is obtained by using the radiation energy and emissivity of the fourth and fifth bands of AVHRR/2.The surface and atmospheric parameters in the radiative transfer equation are known,which can solve the reflectivity of AVHRR/2mid-infrared band.4)Sensitivity analysis of inversion results.The influence of parameters and transfer equation on the error of reflectivity inversion is estimated.The accuracy of the inversion results is verified by comparing the measured surface temperature and atmospheric parameters at different times and different types of surface coverage.