Performance analysis of GPS attitude determination in a hydrographic survey launch

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Attitude determination for hydrographic applications, using simultaneous GPS phase measurements from three antennas, has been investigated in this report. Two main issues were addressed first deals with GPS carrier phase ambiguity resolution and the second deals with attitude determination from GPS measurements. Real time attitude determination is required for a number of applications such as hydrographic surveying with multibeam echosounders. Therefore, a technique capable of determining the ambiguities from a single epoch of data within the time interval defined by successive GPS outputs, has been implemented. This technique is a derivation of the least squares search method, extended to use the known baseline length between antennas to reduce the ambiguity search space. The performance of this techniques has been evaluated using field data, for an antenna spacing of 2.0 and 4.5 metres. The results indicate that the carrier phase ambiguities were successfully solved, for all the data span, when using dual frequency data from a single epoch. This shows that the techniques used is reliable and can be applied to real time attitude determination. GPS attitude was computed using direct determination of heading, pitch and roll. GPS derived attitude measurements were compared with commercial motion sensor data collected onboard a hydrographic survey launch. This comparison indicates that GPS attitude parameters can be determined with an accuracy of 0.07 degrees for a 4.5 metres baseline length, and 0.20 degrees for 2.0 metres baseline.