Study On The Application Of Improved Kriging Interpolation In Low Frequency Additional Secondary Factor Correction

The land-based navigation systems are now widely used in wireless communication,timing,navigation and positioning,weather forecast and other fields.Compared with satellite-based navigation systems,they have the advantages of stable signal propagation and less susceptibility to interference.They can also be used as an important backup for satellite-based navigation systems.However,due to the complex propagation path of ground wave signals and the influence of unpredictable factors such as climate and season,the propagation delay calculation accuracy is low.Among them,the Additional Secondary Factor(ASF)is the key factor influencing the precision.The research on the factors that influence the ASF delay and the correction method had been implemented int this paper.The main work is as follows:Firstly,Explain the three components of low-frequency ground wave propagation time delay.It mainly includes the Primary Factor(PF)affected by the great-circle distance and the refractive index of the atmosphere,the effect of the different speed between sea and air is called the Secondary Factor(SF)and the Additional Secondary Factor(ASF)affected by the effect of the different speed between land and sea,the effect of various factors on time delay is analyzed from the angles of earth conductivity,atmospheric refractive index,great circle distance,etc.Secondly,According to the existing low-frequency ground wave propagation theory,the delay calculation methods and the strengths and weaknesses of the three propagation models are deeply analyzed.The calculation method including the uniform smooth path model includes the Fock diffraction method,the calculation method of the piecewise uniform smooth path model includes the Millington empirical formula and the Wait integral method,and the calculation method of the irregular path model mainly includes the integral equation.Finally,the variation characteristics of delay with distance under various models are analyzed through simulation.Although there are many calculation methods,each has certain limitations,and the theoretical calculation error for complex terrain is relatively large.Lastly,The method of using improved kriging interpolation to build ASF correction library is introduced.The moth flame optimization algorithm is used to realize the automatic fitting of the variogram to reduce the influence of human factors.The fitness function is designed reasonably and the influence weight of nearby sampling points is increased to improve the prediction accuracy of the kriging interpolation.Finally,the sampling area was rasterized and the ASF correction library was established using ordinary kriging and improved kriging.Cross-validation showed that the prediction results were reliable and the improved kriging prediction accuracy was improved to some extent,which solved the ASF delay value.It is difficult to calculate accurately through theory,and it is a problem that large area and high density measurement of ASF value consumes manpower and material resources.