01080511

Monograph

Estimation of rail position and geometry using a high-precision differential Global Positioning System (GPS) can be used to monitor the movement of rail. Because rail naturally expands and contracts during temperature changes, lack of movement during severe temperature change would indicate significant rail stress. Point-specific monitoring can detect slippage of rail down a mountainside or other longitudinal rail movement. High-accuracy measurements might be useful for a variety of future rail applications, including identifying buckle precursors and predicting rail failure. Measurements collected from a moving platform would be most practical for mapping long sections of rail. In this Innovations Deserving Exploratory Analysis (IDEA) project, the author compared raw and post-processed GPS trajectory measurements, collected from a high-railer, to stationary benchmark points. The GPS system had an average error distance of 5-10 cm to the benchmark points. However, there was some calibration error and position variation between the GPS antenna and the rail; this error could be reduced with a more advanced system setup. The bulk of the error came from problems with GPS kinematic convergence. Because of integer ambiguities in the carrier signal, the GPS receiver does not always reliably estimate the correct number of carrier frequency cycles between the receiver and satellites. For short track segments, the integer ambiguity is observed as a constant bias in the data. A least-squares offset was calculated to remove this bias. Signal processing smoothing methods removed some of the inherent jaggedness of the trajectory data. After smoothing and bias removal, many of the trajectory measurements had an average error distance of about 1-2 cm to the stationary benchmark points. This reduced error is what might be achieved if the integer cycle ambiguity problem can be well solved. GPS technology could potentially be used to detect geometric precursors to rail buckles, if such precursors exist. This report presents a buckle detection model that takes as input a rail trajectory corrupted by measurement noise and computes the probability that a low amplitude sinusoidal mode can be identified in the measurement data. The author finds that a GPS system operating at 3 cm accuracy could reliably find a low amplitude sinusoidal mode having amplitude 5-10 cm across a 50 m section.

This HSR-IDEA project was conducted by the University of Illinois, Urbana-Champaign.

HSR-IDEA Project 26

English

34p

2004-2

High-Speed Rail IDEA Program Project Final Report

Final Report

Print

Appendices (1) ; Bibliography; Figures (28) ; Photos (5) ; Tables (7)

Buckling; Detection and identification; Errors; Global Positioning System; Monitoring; Railroad tracks; Signal processing; Technological innovations

Innovations Deserving Exploratory Analysis (IDEA) (Program)

Continuous monitoring

Highways; Maintenance and Preservation; Railroads

TRIS, TRB

Oct 31 2007 10:06AM