Ashtech Application & Tech Note Library

Application Notes and Technical Papers

Application Note #1

Structural Deformation Monitoring Using GPS

The Applied Research Laboratory of the University of Texas at Austin has studied the practicality and potential cost savings for the use of GPS-based structural deformation monitoring systems with millimeter level accuracy using the lowest cost boards available today that employ both code and carrier phase data on the L1 frequency. Guided by the work of Dr. Alan McGown of the University of Strathclyde who describes a comprehensive structural monitoring system as one which provides data at the Micro, Meso, and Macro scales , the ARL team determined that L1 frequency GPS boards that allow for both the code and carrier phase data are most effectively used at the Macro scale and some Meso scale applications where movements between components occur in more than one direction, and can provide a detailed picture of how the overall shape of a structure changes under various loads, through varying environmental conditions , and over time. The ARL system achieves this by strategically positioning a network of sensor nodes, an RF spread spectrum data communications system, and a central data processing and analysis station. Each sensor node consists of a single frequency GPS receiver, micorcontroller, data radio, and power conditioning unit. The GPS boards employed at each sensor node must have high data rates, (For short term movements such as high wind), consume little power, low in price, and have the ability to mitigate the typically largest error source encountered by GPS receivers on and around large, fixed structures...multipath.

In April of 1997 and after months of testing any and all GPS boards who claimed to meet the ARL's high demands for quality and cost effectiveness, two GPS boards were selected to participate in a system demonstration for the Scottish Government conducted at the University of Strathclyde against conventional surveying techniques used in the past. This demonstration would decide the acceptance the deformation monitoring system to be used for the retrofitting of five bridges in Scotland, as well as provide a proof of concept for the U.S. Federal Highway Administration who was in attendance. The two boards chosen were the Novatel RT-20 and the Ashtech G12. During the demonstration, it became clearly evident that the logical choice would be the Ashtech G12 based on its performance compared to the Novatel unit.

Author: Kurt Simon - Navigation Sales Dept. October 1997.

1. CARRUTHERS D, TELFORD I, MCGOWN A, and MILNE P. 1995: "Structural Health Monitoring of the Kingston Bridge, Glasgow, UK", 20th World Road Congress, Permanent International Association of Road Congresses.