Liwen Dai

Pseudo-Satellite Applications in Deformation Monitoring

In this article, three general classes of potential pseudolite applications for deformation monitoring are described. The first is GPS augmentation with pseudolite(s), which is suitable for circumstances such as urban canyons, or for monitoring in valleys and deep open-cut mines. The second is indoor applications of pseudolite deformation monitoring systems. Pseudolite arrays can, in principle, completely replace the GPS satellite constellation. This could extend the “satellite-based” deformation monitoring applications into tunnels or underground, where GPS satellite signals cannot be tracked. The last case is an inverted pseudolite-based deformation monitoring system, where a “constellation” of GPS receivers with precisely known “orbits” track a mobile pseudolite. The system consists of an array of GPS receivers, the base reference pseudolite, the mobile pseudolite, and a central processing system. However, in the case of such pseudolite-only or hybrid pseudolite-GPS deformation monitoring systems, some additional issues need to be addressed. These include multipath, atmospheric delay effects, and pseudolite location-dependent biases. To address deformation monitoring applications, some practical procedures to mitigate or eliminate their influence are suggested. Some experiments were carried out using NovAtel GPS receivers and IntegriNautics IN200CXL pseudolite instruments. The experimental results indicate that the accuracy of the height component can indeed be significantly improved – the RMS of the vertical component has been reduced by a factor of 4, to the same level as the horizontal components. Their performance will be demonstrated through case study example.

INVERTED PSEUDOLITE POSITIONING AND SOME APPLICATIONS

Abstract In this paper the inverted pseudolite positioning system, compnsmg a ‘constellation’ of GPS receivers that tracks a mobile pseudolite, is discussed Two configurations of the inverted positioning system are described The implementation challenges for the pseudolite-based inverted positioning system, including geometry optimization, multipath mitigation and minimization of the impact of GPS receiver location errors, have been investigated Several applications of the inverted positioning concept have been identified, including deformation monitoring and navigation services based on pseudolite installed on stratospheric airships. A static experiment was carried out using six NovAtel GPS receivers and two IntegriNautics IN200CXL pseudolite instruments, on the UNSW campus, on the 4th April 2001. The experimental setup and operational procedures are described in detail. The carrier phase measurements have been processed in an ‘inverted’ mode. The results indicate that the potential accuracy of ‘inverted’ phase-based positioning is better than 5mm. The static experiment has indicated that the two configurations for the inverted positioning are feasible in practice.