Three years ago, engineering survey company G & C Sadlier Design was engaged to perform a route selection and centerline pegging survey for a gas pipeline duplication between Somerton in Victoria and Young in New South Wales, Australia. To accomplish the work, G & C Sadlier Design turned to FOIF GNSS receivers.
So far, about 225 kilometers have been surveyed and constructed, with 306 kilometers still to be surveyed, designed and built, according to surveyor Greg Sadlier. The current focus is a 100-kilometer section in Victoria and a 70-kilometer section in New South Wales. Recently completed are two linear static control surveys over 80 kilometers in Northern Victoria and 70 kilometers at the end of the project near Young in New South Wales.
“These surveys have been done using a FOIF F60 Base GNSS receiver and two FOIF A30 Rover receivers. (Two one-man survey crews are used),” Sadlier said. The procedure is to set up the F60 base over a point with known coordinates and elevation, approximately in the center of the alignment to be surveyed.
The base was set first, to record 1-second data to the datacard over the duration of the survey. One surveyor started the base, and surveyed forward to the end of the alignment, and the other rover crew started at the beginning of the alignment and surveyed towards the base. The rovers were also set to record 1 second data to the datacard.
“The control points were 0.75-m steel star pickets driven flush with the ground surface, and witnessed with a galvanized 1.5-m steel star picket,” Sadlier explained. “Each rover point was surveyed for 20 minutes plus 1 minute per kilometer of the distance to the base. That is, a point that is 35 Km from the base will be occupied for 55 minutes or 3300 epochs. With the control points at easy accessed positions, usually roads crossing the alignment, at intervals of about 8 kilometres mean that the survey of 80 Km is completed in one day.
“We have found the FOIF GNSS receivers are very easy to use, and the epoch readout on screen is very reassuring that the data is being stored, and easily confirms that the correct amount has been stored. The data is easily downloaded from the card and converted to Rinex format with FOIF RnxTransform. The data was post processed by a third party.”
The control survey results were adjusted (Helmert adjustment) onto check Permanent Marks at both ends. “This made a rotation of 0°00’00.001” and a shift of 0.007 meters E and 0.005 meter N. An elevation difference of .035 meters was manually adjusted out over the 80 kilometers,” Sadlier said.
“We are now using the control survey while surveying the route selection and features survey,” Sadlier said. “We have two RTK base locations at the 25-kilometer mark and 52-kilometer marks, and using our VHF radio solution have coverage over the entire job with a 10-kilometer overlap in the center.
“We have found that RTK observed control readings of 180 epochs return residuals of less than 010 meters for both coordinate and elevation for all the static control points. Very impressive results considering the length of the survey,” Sadlier said.
The engineering firm has yet to process the New South Wales data, but expects the same or better, Sadlier said, as the overall length is a little less and the surveyed control points were in more open country with less tree cover.
