Craig Roberts

Reducing GPS carrier phase errors with EMD-wavelet for precise static positioning

Abstract In this paper, a new EMD-Wavelet based model is used to reduce carrier phase errors for precise static GPS positioning. The EMD is a new signal processing method for analysing non-linear time series, which decomposes a time series into a finite and often small number of Intrinsic Mode Functions (IMFs). The decomposition procedure is adaptive and data-driven. The IMFs are stationary which are more suitable for wavelet analysis. The merits of both the EMD and Wavelets are combined to produce an improved EMD-Wavelet systematic error extraction model. Thereafter, a method of the GPS baseline calculation based on the EMD-Wavelet systematic error mitigation model is suggested. The experimental results show that the proposed scheme dramatically improves the reliability of ambiguity resolution with a larger F-ratio and W-ratio index after systematic error elimination.

Chiral susceptibility and the scalar Ward identity

The chiral susceptibility is given by the scalar vacuum polarization at zero total momentum. This follows directly from the expression for the vacuum quark condensate so long as a nonperturbative symmetry preserving truncation scheme is employed. For QCD in-vacuum the susceptibility can rigorously be defined via a Pauli-Villars regularization procedure. Owing to the scalar Ward identity, irrespective of the form or Ansatz for the kernel of the gap equation, the consistent scalar vertex at zero total momentum can automatically be obtained and hence the consistent susceptibility. This enables calculation of the chiral susceptibility for markedly different vertex Ansatze. For the two cases considered, the results were consistent and the minor quantitative differences easily understood. The susceptibility can be used to demarcate the domain of coupling strength within a theory upon which chiral symmetry is dynamically broken. Degenerate massless scalar and pseudoscalar bound-states appear at the critical coupling for dynamical chiral symmetry breaking.

Low-cost GPS-based volcano deformation monitoring at Mt. Papandayan, Indonesia

Abstract The global positioning system (GPS) can be utilised to detect ground deformations of the surface of a volcano. Ground deformation monitoring is considered one of the most effective tools for investigating the behaviour of active volcanoes. The decreasing cost of GPS hardware, together with the increased reliability of the technology, facilitates such demanding applications. GPS ground deformation measurements can be continuous, automatic, conducted in all weather conditions, and provide three-dimensional positioning results. Higher computing power also means that the complex mathematics required to process GPS baselines can be easily handled in near real time. During the past few years a methodology has been developed for processing data collected by GPS networks consisting of a mixed set of single-frequency and dual-frequency receivers. The strategy is to deploy a few permanent, ‘fiducial’ GPS stations with dual-frequency, geodetic-grade receivers surrounding an ‘inner’ network of low-cost, single-frequency GPS receivers. Such a configuration offers considerable flexibility and cost savings for geodynamic applications such as volcano deformation monitoring, which require a dense spatial coverage of GPS stations, and where it is not possible to establish permanent GPS networks using only expensive dual-frequency instrumentation. This configuration has recently been tested at the Mt. Papandayan volcano in West Java, Indonesia. The two-stage network design consists of an inner network of four single-frequency Canadian Marconi (CM) GPS receivers surrounded by three dual-frequency Leica CRS1000 GPS receivers. The inner network logged and transmitted GPS data from the ‘slave’ stations located on the volcano, to a base station. The combined processing of the CM and Leica receiver data was performed off-line so as to investigate the performance of such a mixed-mode system. The basis of the processing methodology is to separate the dual-frequency, ‘fiducial’ station data processing from the baseline processing involving the single-frequency receivers on the volcano. The data processing for the former was carried out using a modified version of the Bernese software, to generate a file of ‘corrections’ (analogous to Wide Area DGPS correction models for the distance dependent biases – primarily due to atmospheric refraction). These ‘corrections’ were then applied to the double-differenced phase observations from the inner receivers to improve the baseline accuracies. A description of the field testing (and its challenges) during February–March 2000, together with a discussion of some of the results are presented.

Continuously operating GPS-based volcano deformation monitoring in Indonesia: the technical and logistical challenges

In the past decade or so there has been increasing interest in the use of permanent, continuously-operating GPS networks, with a small number of continuous networks having been deployed in the USA, Japan, Canada and Europe for large scale crustal motion studies. However, only in Japan has a country-wide continuous GPS network to support seismic research been established by the Geographical Survey Institute (GSI). Even with such a dense network of dual-frequency GPS receivers the station separation is of the order of 20km or more. There are, however, applications of GPS-based deformation systems which require receiver densities of the order of just a few kilometres. Furthermore, the high cost of geodetic GPS receivers means that many countries cannot afford to establish such networks. Applications of dense permanent GPS arrays include monitoring of volcano flanks, micro-faults, ground subsidence due to underground mining or fluid extraction, slope stability, and even engineering structures such as dams, bridges, etc. This paper describes a low-cost design of an automatic GPS-based volcano deformation system that has recently been deployed by the authors on the Papandayan volcano in Indonesia. The critical problems that had to be overcome will be described, and early results presented.

A High-Precision Deformation Model to Support Geodetic Datum Modernisation in Australia

This paper describes a gridded kinematic representation of a deformation model that can be used to support kinematic geodetic datum applications for high precision users. The kinematic model is comprised of a site velocity model (for coordinate prediction and to model inter-seismic deformation and plate motion) and an epoch correction (patch) model. The epoch correction model estimates distortion between reference frames at the reference epoch and can include episodic deformation arising from seismic activity.

Realisation of a Geodetic Datum Using a Gridded Absolute Deformation Model (ADM)

This paper describes a schema for a gridded absolute deformation model (ADM) and non-linear deformation patch model that can be used to transform point positions captured in the International Terrestrial Reference Frame (ITRF), or other closely aligned reference frame, to a reference epoch consistently over time for practical applications. The schema described utilises existing models of rigid plate motion, plate boundary deformation and non-linear deformation (e.g. coseismic and postseismic effects or subsidence). Application of an ADM and patch model can enable consistent Precise Point Positioning (PPP) over time and seamless integration of Continuously Operating Reference Station (CORS) networks within deforming zones. The strategy described can also ensure consistency of time-tagged spatial datasets (e.g. laser scanned point clouds and digital cadastral databases) and GIS within a kinematic environment. An ADM can also be used as the basis for static epoch projections of a national or regional kinematic datum. A case study from New Zealand is described.

Kinematic positioning using a robotic total station as applied to small-scale UAVs

Modern robotic total stations (RTS) have the ability to automatically aim, search and track moving targets at high precision thereby enabling kinematic positioning. However, the internal subsystems of the RTS (distance and direction) exhibit time delays which limit the precision positioning of a moving target. These effects are investigated with tracking experiments on a known circular and linear path. A second part of this research investigates small-scale unmanned aerial vehicles (UAV) which use navigation quality GPS as a priori coordinates for photogrammetric processing of acquired images. RTS kinematic positioning was applied to a UAV in a field trial to improve a priori image coordinates and evaluate the method for direct geo-referencing.

Special feature – managing the dynamics of the New Zealand spatial cadastre

In 1995, a dynamic cadastre, based on a dynamic geodetic datum, was proposed for New Zealand to recognise that all cadastral boundaries are in motion. Subsequently New Zealand implemented a semi-dynamic geodetic datum which is accompanied by a deformation model. In 2010 and 2011, the Canterbury region in the South Island of New Zealand was subjected to a sequence of earthquakes that resulted in some boundaries being ruptured by up to 4 metres. A set of localised deformation models was developed to model the seismic movements. The implementation of these models and their accuracy are addressed in this paper.

Permanent Automatic GPS Deformation Monitoring Systems: A Review of System Architecture and Data Processing Strategies

Ground deformation due to volcanic magma intrusion, crustal motion, ground subsidence, etc., are phenomenon ideally suited for study using GPS. The change in length, height difference and orientation of baselines connecting GPS receivers in a carefully monumented ground network can be monitored. This is done by repeatedly measuring the same baseline components to an accuracy commensurate to, but preferably much higher than, the expected baseline component changes. Such GPS techniques are based on the “campaign” principle: the periodic (often annual) re-survey of a network of control points. However, over the last half decade or so, there has been a growing interest in the deployment of permanent, continuous GPS monitoring networks. The factors responsible for this trend include the declaration a few years ago of Full Operational Capability of the GPS system, and the steady decrease in price, size and power requirements of GPS receivers. Important additional factors have been the high cost of annual GPS surveys (manpower, travel, logistics, etc.), as well as the fact that geo-scientific research can be furthered because of the continuous measurement of a deformation phenomenon, rather than its periodic measurement.

A Two-Frame National Geospatial Reference System Accounting for Geodynamics

This paper presents a high level proposal for how a Local Reference Frame (LRF) could be implemented alongside the International Terrestrial Reference Frame (ITRF) as part of a two-frame national geospatial reference system. By accounting for both local and global geodynamic effects using time-dependent transformations, the LRF can minimize the complexity that results when objects that are fixed with respect to the ground have continuously time-varying coordinates in a global frame.