Precise Marine DGPS Positioning Using P Code and High Performance C/A Code Technologies

The objective of this paper is to assess and compare the capability of P code and high performance C/A code receiver technologies for survey launch positioning at sea water to the sub-metre level. The receivers used to assess these technologies are the dual frequency Ashtech P-XII and the single frequency NovAtel GPSCardrM. Sea trials were conducted at velocities of 10 to 15 knots using both receiver types simultaneously to collect the data necessary for the evaluation. Two data processing methods are analysed, namely ambiguity resolution on the fly and carrier phase smoothing of the code. The survey launch environment is relatively harsh Lachapelle et al, The University of Calgary with code and carrier phase multipath being a major error source. Ambiguity resolution on the fly is successful using the widelaning capability of the dual frequency P code. Ambiguity determination using single frequency data is also possible but the observation time required is substantially longer. In this case however, the use of a twin receiver system on the launch contributes in this case to improving the reliability of the solution. The effectiveness of chokering groundplanes to decrease the time to ambiguity resolution by reducing carrier phase multipath is demonstrated. DGPS P and high performance C/A code results in rrns accuracies are at the one metre level. A slight improvement is achieved using carrier phase smoothing of the code.