Design Of Spaceborne Multi-angle Thermal Infrared Payload Angle Index For Upward Longwave Radiation Estimation

The upward long-wave radiation on the surface is an indicator that reflects the cold and warm conditions of the earth's surface,and is one of the key variables of the surface radiation budget.In the existing estimation algorithms for the products of the surface upward long-wave radiation,the surface is assumed to be Lambertian,and avoiding the directivity of the surface thermal radiation will bring great errors to the estimation of the surface long-wave upward radiation.Multi-angle synchronous observation of the same object is the most direct and effective method to solve the directivity of thermal radiation.However,at present,only ATSR series sensors can provide quasi-synchronization at two angles(0° and forward 55°)at the satellite scale.The two angles are not enough to drive the directional kernel-driven model of thermal radiation to achieve angle correction,and it is urgent to develop satellite payload multi-angle observation methods.Facing the research on the directionality of thermal radiation,the current forward models mainly include five categories: radiation transfer model,geometric model,hybrid model,computer simulation model and parameterized model.The kernel-driven parametric model can be directly applied to satellite multi-angle data processing because of the few input parameters and the simple and fast solution.There are six widely used kernel drive models in the thermal infrared field,including RL,Vinnikov,Ross-Li,LSF-Li,VinnikovRL and LSF-Chen models,which are designed for angular correction of surface temperature.However,the fitting ability of these six models under limited observation conditions is unknown,which makes it difficult to choose a suitable model in the application.In order to solve the above problems,this article has carried out the following three parts of work :1.This paper uses the 4SAIL model to simulate 30,600 sets of multi-angle directional brightness temperature(DBT)data sets.At the same time,in order to consider the influence of errors,a random error of [-1.0,1.0] K is added to the simulated data set.A total of 886 sets of angle combinations are used to drive these six kernel-driven models,which are suitable for 21960 DBTs for 30,600 sets of 4SAIL simulations.The RMSE of each combination and the root mean square error(RMSE)of all 886 finite angle combinations are used to evaluate the overall fitting ability of the six kernel-driven models.It is found that the LSF-Chen model has the best fitting ability under limited angles.2.Further use WIDAS aviation data to verify the fitting ability of the LSF-Chen model under aviation data.At the same time,in order to verify the influence of the directivity of thermal radiation on the upward long-wave radiation,the hemispherical SULR is taken as the theoretical true value,and the accuracy of the thermal radiation estimation results in nineteen single directions(-45° to 45° with 5° steps)is compared and analyzed.As a result,it is found that most of the single-angle estimation results of upward long-wave radiation are obviously overestimated compared with the results of hemisphere estimation of upward long-wave radiation.3.Using the best-fitting kernel-driven model(LSF-Chen)obtained from the above analysis as a tool for fitting hemispherical thermal radiation,it focuses on 220 combinations of different numbers of angles(including 45 combinations of five angles,Select the optimal observation angle combination from the seven-angle combination 84 kinds,nine-angle combination 70 kinds,and eleven-angle combination 21 groups),and finally choose the angle combination(0°,±25°,±60°).