How well can online GPS PPP post-processing services be used to establish geodetic survey control networks?

Abstract

Establishing geodetic control networks for subsequent surveys can be a costly business, even when using GPS. Multiple stations should be occu- pied simultaneously and post-processed with scien- tific software. However, the free availability of online GPS precise point positioning (PPP) post-processing services oer the opportunity to establish a whole geodetic control network with just one dual- frequency receiver and one field crew. To test this idea, we compared coordinates from a moderate- sized (P550 km byP440 km) geodetic network of 46 points over part of south-western Western Australia, which were processed both with the Bernese v5 scien- tific software and with the CSRS (Canadian Spatial Reference System) PPP free online service. After re- jection of five stations where the antenna type was not recognised by CSRS, the PPP solutions agreed on average with the Bernese solutions to 3.3 mm in east, 4.8 mm in north and 11.8 mm in height. The average standard deviations of the Bernese solutions were 1.0 mm in east, 1.2 mm in north and 6.2 mm in height, whereas for CSRS they were 3.9 mm in east, 1.9 mm in north and 7.8 mm in height, reflect- ing the inherently lower precision of PPP. However, at the 99% confidence level, only one CSRS solution was statistically dierent to the Bernese solution in the north component, due to a data interruption at that site. Nevertheless, PPP can still be used to estab- lish geodetic survey control, albeit with a slightly lower quality because of the larger standard devia- tions. This approach may be of particular benefit in developing countries or remote regions, where geo- detic infrastructure is sparse and would not normally be established without this approach.