On site scanning

Large Scale GNSS Survey - Benchmark Survey

Description of Project

Eliot Sinclair were engaged by Stronger Christchurch Infrastructure Rebuild Team (SCIRT) to carry out a large scale GNSS survey for the purpose of verifying a benchmark network that was established 18 months earlier for the purposes of the Christchurch rebuild.

Description of task undertaken

155 Marks in a 28500ha area were re-surveyed over 5 weeks with a total of 1438 observations. These had to be scheduled in fine weather to minimize atmospheric errors. Prediction of VDOP / PDOP spikes to avoid satellite errors also influenced the scheduling of observations to ensure high quality data. The re-survey was fully documented with field notes and photographs.

How the Problem was solved

A least-squares network adjustment was undertaken in Trimble Business Centre software to compute the final coordinates and the Land Information New Zealand SNAP program was used to independently check these results. The results of this re-survey were used to assist in the analysis of ground movement over the 18 months prior to the survey. LINZ subsequently published a precise normal-orthometric level dataset for Canterbury benchmarks on 19th June 2013.  This dataset overlapped the SCIRT  network observed by Eliot Sinclair at 70 marks and was considered as the best source of values to calculate local vertical datum offset between NZVD2009 and Lyttelton 1937. A series of analytical reports were provided to communicate results to the client and government agencies. Raw observations were supplied to LINZ for their inclusion in the greater Canterbury Network.

Future enhancements

With 26 years’ experience with GPS & GNSS surveying Eliot Sinclair continually provides reliable, high integrity survey control datasets. We seek to challenge our staff at all levels, with great opportunities for junior staff to up-skill and complete complex surveys to the highest of standards.

48x48-pdfBulletin 13002: Large Scale GNSS Surveys, written by Melissa O’Brien, Graduate SurveyorPhone2image004