Fast RTK Applications of the Leica CRS1000 GPS Receiver

GPS has been used widely for many real-time, high precision kinematic applications in the last few years. Such applications cover a wide spectrum of platforms, which take advantage of the very high sampling rates of modern GPS receivers (10-20Hz). These include the "GPS sea swell gauge" and the "GPS seismometer". At the University of New South Wales (UNSW) a number of fast RTK (real-time kinematic) experiments using the new Leica CRS1000 receivers were carried out. One receiver was considered the mobile (setup to record fast RTK positions), and the other was the reference receiver. The vibration on the GPS antenna, to simulate the sea swell or seismic wave, was generated using a mechanical shaker. The shaker was oriented both vertically and inclined to 45 degree (with the antenna facing north). The Fast Fourier Transform was used to analyse the recorded fast RTK results and it was found that when the vibration with frequency 2.3Hz or 4.3Hz was applied, all the signals were clearly resolved. This demonstrates the feasibility of using GPS receivers as "seismometers". An adaptive Finite-duration Impulse Response (FIR) filter, based on a least-mean-square (LMS) algorithm, has also been developed to successfully derive a relatively noise-free seismic signal in real-time, from the high-rate RTK GPS results. A technique developed at UNSW for determining high precision coordinates of a mobile receiver over baselines up to 1000km in length, even when the ambiguities were not resolved correctly, can be used with high data-rate receivers such as the CRS1000 for measuring sea swell. This paper describes the concept and methodology of a possible GPS sea swell gauge.