The Processing Of In-situ Thermospheric Density Observations And Empirical Density Model Calibrations

Precise orbit is the foundation of the modern aerospace activities and space applications.The orbit has already attained the unprecedented accuracy with advanced tracking system aiming at observing some geodetic satellites.The accuracy of dynamical model is one of the most key factors affecting orbit calculation precision presently.In the past 20 years,a lot of improvements have been made in earth gravity field model,surface force model such as solar pressure and earth albedo,as well as some empirical acceleration compensations.It contributes to the dynamical models modelling dramatically.Unfortunately,atmospheric drag model,due to uncertainties of atmospheric densities and drag coefficients,has been the limited factors of improving precision of orbit determination and prediction,especially the 15% accuracy bottleneck of empirical density models.The models used in domestic engineering field are released at least 20 years ago by US and European community.The thermospheric density observations autonomously are very scarce,and related work on atmospheric density modelling is just started in China.Therefore,the work discussed in this dissertation will lay a solid foundation on subsequent empirical density modelling by ourselves,including in-situ data processing and calibrating,accuracy assessment of present empirical density models and empirical density model calibrating.Firstly,a brief introduction has been made about the atmospheric payload on the first Atmospheric detecting and Precise Orbit Determination(APOD)experimental satellite.We discuss the working principle and the method of in-situ data processing.In the light of traditional calibration using empirical density model,a new dynamical calibrating method has been given based on derived densities from precise orbit or twoline elements.The comparison results show that the dynamical calibrating method can reduce the bias of observations dramatically,which also can gurantee the independency and reliability of observations.Secondly,aiming at the widely used empirical density models,such as JacchiaRobert(JR),NRLMSISE00(MSISE00),JB2008 and DTM2013,a comprehensive accuracy assessment has been made from two aspects,which are the densities accuracy itself and orbit calculation effects.Statistical results display that the newly released JB2008 and DTM2013 models show better performance than JR and MSIS00 models.However,there are some restrictions on obtaining the source code of DTM2013 and driven parameters of JB2008,Jacchia-Robert,a density model with relative lower accuracy,has to be the choice as the base model of calibration.Finally,calibrated parameters are chosen according to sensitivity analysis,some partial derivatives are deduced,and a calibrating algorithm is given.Still from two aspects as mentioned before,some comparisons have been made between two different calibrating methods.One is that just calibrating temperature constant(Tc),the other one is that calibrating the coefficients of expanded spherical harmonic function.Calibrated results show that two methods both can reduce the bias of density model itself,and make some improvements on accuracy of orbit determinations.But it doesn't always work on orbit prediction,the best performance of improving accuracy of predicting 24 h is 64.4% in Jan and Feb,2003,based on CHMAP derived densities and Rapid Scientifical Orbit.Therefore,the effect of drag coefficients on orbit prediction has been analyzed further.