Slow Structural Deformation Monitoring Using Locata - a Case Study at the Tumut Pond Dam

A Global Navigation Satellite System (GNSS) is a very popular technology for „24/7‟ monitoring of slow structural deformation. Unfortunately a GNSS is dependent on the number as well as geometric distribution of the available satellites, and the precision may therefore vary at different observation times. On the other hand, Locata Corporation‟s positioning technology, known as “Locata”, provides centimetre level accurate position solutions with millimetre noise level for static positioning using carrier phase data. This provides an advantage over other technologies for monitoring structural movement in many applications. The Locata network can be deployed around a structure that would ensure optimal network geometry under site constraints. Previous investigations have demonstrated the applicability of Locata for deformation monitoring. This paper describes a deformation monitoring trial conducted at the Tumut Pond Dam near Cabramurra, NSW, Australia. After analysing network geometry for precession, as well as site constraints (such as line-of-sight visibilities, power, security, etc.) a Locata network, composed of four LocataLites (or transceivers) and a Locata receiver, was established. Locata pseudorange and carrier phase measurements, and atmospheric data were collected and post-processed using a sequential least squares estimation technique. Measurement data was used to obtain 3D coordinate solutions, and these coordinate solutions were checked for statistically significant deformation using standard deformation analysis procedures. It was observed that, with 2mm horizontal and 5mm vertical component precision (95% CI), Locata provided position solutions that could identify any statistically significant movement.