The ambiguity resolution for the long-range baseline has been a challenge due to large ionospheric delay and tropospheric delay. A Triple Search Ambiguity Resolution (TSAR) method to estimate the ionospheric delay, tropospheric delay and ambiguities instantaneously for long baseline RTK is proposed in this paper, which reserves the integer nature of ambiguity. The experiments demonstrate that ambiguity resolution can be achieved within 8 epochs for 70 Km baseline with the TSAR method using BeiDou observation alone, and only 4 epochs are required to fix the ambiguity using both BeiDou and GPS observation. And the speed for the ambiguity fixing time is improved over 10 times with TSAR method, compared with traditional long-range ambiguity resolution method.

Keywords: Network RTK, ambiguity resolution, tropospheric delay, ionospheric delay, long-range baseline