مدلسازي خطاي يونسفري با استفاده از تصحيح مولفه هاي مختصات و بردار موقعيت

Ionospheric Modeling Based On 3-D Coordinates And Position Vector

In this paper we are presenting a methodology, which can remove the effect of ionospheric refraction (ionospheric error) on the coordinates derived by single frequency GPS receivers up to 85 percent at a radius of 1400 km around the computational point. The method is based on the GPS observations being made at the permanent GPS stations, according to the following procedure: (i) The real-time GPS observations being made at the permanent GPS station is compared, epoch-wise, with precisely known coordinates of the permanent station and the time series of coordinate variations in x , y , and z component {(Delta)xi,(Delta)x,(Delta)z} is derived. (ii) Fast Fourier technique is applied in order to transfer each components of the variations vector {(Delta)x, (Delta)y, (Delta)z} from the time domain into frequency domain. (iii) The plot of the resulted periodogram provided us with the frequency vector { fx, fy, fz} of the ionospheric refraction (ionospheric error) with nearly 24 hour period. (iv) Having derived the frequency vector { fx fy, fz } of the ionospheric refraction, a sinusoidal models of the form o-xi = Alfa^i0 + Alfa^i1 cos(w^i*t -Phi^i ) (where w = 2(Pi) f) is fitted to the coordinate differences {(Delta) x, (Delta)y, (Delta)z} via least squares technique. As a permanent GPS station of Tehran National Cartographic Center (NCC) is used.