Reseach On Broadcast Ephemeris Interpolation And Precise Ephemeris Extrapolation

GPS(global positioning system)is a satellite navigation system of new generation established by American,since it has a series of advantages such that it is full time working and global,and it doesn't need to be seen between stations and have a fast measure volecity and accuracy,it is widely used in surveying,navigation and climate. Meanwhile,we need the GPS satellite ephemeris to be more accurate. satellite ephemeris is the premise and base for satellite positioning,the accuracy of the orbit will directly influences the accuracy and result of positioning. Although broadcast ephemeris is less accurate than precise ephemeris,it can be acquired real time and easily and is used by many users of navigation and positioning.We usually use function approximation to get the expression of satellite orbits when we calculate, coordinates interpolation and orbit fitting are two algorithms to orbit approximation. So,this paper dealt with at the present stage ephemeris used in the interpolation and fitting methods of verification, analysis of test results,the satellite coordinates of extrapolation.(1)First we use broadcast ephemeris to calculate some samples in the time of interpolation. Then we interpolate the satellite coordinates with Lagrange and chebyshev polynomial.Meanwhile we analyze the precision of the coordinates according to different polynomial orders and samples.(2) Selecting a specific time to interpolate the coordinates and choosing the same number of samples before and after the time,the interval of each samples is 15 minutes,so the time of interpolation is in the middle of the fitting curve and the precision of interpolation is high. And this method is applied in practice.(3)Afterwards we make a comparision between the precision of the broadcast ephemeris and the precise ephemeris after Chebyshev interpolation in the same time, and analyze the error,so we can have a reference of accuracy for the next step to extrapolate the satellite coordinates. (4) We use the 15-minute interval precise ephemeris file to interpolate the 5-minutes ephemeris and extrapolate it.We use Lagrange and chebyshev polynomial to extrapolate the coordinates in the processing.And we analyse the precision of extrapolation coordinates according to different orders of the polynomial.Then we select a relatively high precise extrapolating results to extrapolate in long intervals and make a comparision to broadcast ephemeris and research the upper limits of the interval of extrapolation.