Performance experiment of an NNSS positioning in and around Syowa station, East Antarctica.

Since the region concerned is covered with the auroral zone, the received pass number and Doppler frequencies are likely to be affected by the disturbance in the ionosphere. By using carefully selected satellite passes, the convergence of broadcast ephemeris positioning is examined. The convergent process can be approximated by a curve which is inversely proportional to the square root of the accepted pass number with the coefficient of 15 m. The most probable convergent solution however cannot be improved better than 0.6 m. When the absolute accuracy of broadcast ephemeris positioning is estimated by referring to the precise ephemeris positioning results, it can also be given by similar formulae of the above convergence with a somewhat greater uncertainty coefficient of 37 m as proposed by LeRoy. In the counting of Doppler frequencies, it seems most preferable to apply the receiver time frame at the Doppler cross over. The effect of tropospheric correction appears mainly on height solution when the pass geometry is well balanced. The pass imbalance geometry of east- or west-going passes in the antarctic region mostly results in a 5 m longitudinal shift of the most probable convergent point.