Toshiaki Tsujii

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.

Tropospheric heterogeneities corrections in differential radar interferometry

Differential radar interferometry (DInSAR) has been used more and more widely to monitor crustal deformations due to underground mining and oil extraction, earthquakes, volcanoes, landslides, and so on. However, tropospheric heterogeneities have been identified as one of the major errors in DInSAR, which can be up to 40 cm as derived from dual-frequency GPS measurements in the example given in this paper. Therefore, it is crucial to correct the tropospheric heterogeneities in the DInSAR results for monitoring crustal deformation. These corrections from several GPS stations in the radar imaging area can be interpolated and applied to the DInSAR results. The discussions are based on data from the Tower Colliery test site southwest Sydney, Australia.

AUGMENTING GPS BY GROUND-BASED PSEUDOLITE SIGNALS FOR AIRBORNE SURVEYING APPLICATIONS

Abstract This paper discusses some issues associated with the implementation of ground-based pseudolite augmentation for GPS airborne surveying applications. For instance, not only should two antenna offsets (one on the top of, and the other underneath, the platform) be corrected for, but the number, the location, and the geometric distribution of the pseudolites on the ground has to be carefully considered. Initial analyses have shown that the accuracy requirement for the attitude parameters is dependent on the magnitude of the offsets between the two antennas. In addition, a series of simulations has demonstrated that pseudolite augmentation can significantly improve the quality of the positioning solutions, especially the vertical component accuracy (due to the negative elevation of the pseudolites). The optimal number and locations of the pseudolites are dependent on the satellite geometry. Based on selected optimization criteria, a comprehensive search would typically be needed for a specific application. A geometric analysis and measurement testing procedure for this purpose will be described in this paper.

Digital Satellite Navigation and Geophysics: Geophysical measurements using GNSS signals

“And whilst all these nations have magnified their Antiquities so exceedingly, we need not wonder that the Greeks and Latines have made their first Kings a little older then the truth.” Sir Isaac Newton, The Chronology of Ancient Kingdoms, Chap. VI . Though GNSS satellites are just some among many other satellites which are implemented for geophysical measurements, GNSS play a very significant and increasing role in collecting geophysical data. They have become an indispensable tool for many geophysical applications. Apart from this, GNSS satellites have also allowed spread spectrum radiowave technology to mature. This technology can be used on its own for atmosphere probing in other parts of the electromagnetic spectrum than GNSS’s. Together with other atmosphere sensing instruments, GNSS provides information for weather prediction and monitoring climate change. GNSS has also become an essential tool for estimation of the Earth’s rotation parameters. There are also emerging areas of paramount importance, which are yet under development, such as using GNSS signals for earthquake studies. Figure 11.1 depicts the subject of this chapter in relation to other chapters in this book. Data from global reference networks are routinely used to monitor movement of the Earth’s tectonic plates relative to each other and to an inertial frame. In this task the same type of GNSS observables as described in Chapter 8 are used. Such observables are created using measurements from globally distributed networks of GNSS receivers, supplying various data in raw data formats, mostly in RINEX. The most prominent among such networks is the IGS network. There are also various regional and local networks, which can provide large volumes of geophysical information. Among such networks, for example, is the Geographical Survey Institute (GSI) network in Japan, which consists of more than 1200 high-end geodetic GNSS receivers. The data from these networks include code and carrier phase measurements, Doppler measurements, and signal-to-noise ratio. All measurements are delivered from dual frequency receivers using two frequencies (L1, L2). We consider implementation of data from such networks in Sections 11.1, 11.3, and 11.4.