Automated dam displacement monitoring using a robotic total station
An automated data collection and processing system has been created for geodetic monitoring of point displacements at a large earthfill dam project in southern California. Because of the size of this facility, currently the largest earthfill dam project in the United States, the geodetic monitoring program could not be affordably implemented using traditional survey techniques. Therefore, a system was designed that uses a network of permanently installed robotic total stations (RTS) to carry out the measurements and data processing in a fully automatic fashion, with updated point coordinates delivered to the system operator after each measurement cycle. Implementation of this automated monitoring system required the development of specialized software to carry out data collection and processing. Because the robotic total stations were to be housed in observation shelters with glass windows, it was necessary to employ data processing algorithms that would not be unduly affected by the resulting refraction effects. This was achieved by treating each observing station as a standalone monitoring system, eliminating the need to combine the biased RTS measurements with external data sources while still recognizing that refraction effects will cancel out in the computation of point displacements. The automated monitoring system was first activated in October 2000, and has successfully collected displacement measurements for more than a year. A preliminary evaluation of data collected by the system shows that atmospheric refraction has a significant effect on the accuracy achievable during individual measurement cycles. However, averaging measurements collected at different times of day allows the system to meet its design goal of detecting displacements larger than 10 mm at the 95% level of confidence.