GPS COMPASS: A Low Cost GPS Direction Sensor of Two Antenna Type

摘要

This paper describes a low cost GPS direction sensor of two antenna type -GPS COMPASS - which is a device for providing a vessel's heading such as a gyrocompass would provide. It consists of an antenna unit and a processing unit. The antenna unit consists of two antennas with pre-amplifiers which have been designed to have the most suitable gain and radiation pattern for accurate carrier measurements. The processing unit consists of a microprocessor, two GPS receivers and auxiliary sensors. The GPS receivers are from JRC's land mobile division and are very low cost. Direction angle is derived from satellite's positions and double difference of carrier phase data output from the receivers. An integration filter is designed to combine optimally direction data derived from GPS receivers and angles measured by the auxiliary sensors. The algorithm is developed to be compact and executable on even a one-chip microprocessor. In conjunction with the two antennas, direction, roll and pitch angles are derived from the GPS receivers and auxiliary sensors. The features of this two antenna type are higher availability, easier installation and lower cost than three or more antenna types. Compared with a gyrocompass, its settling time is extremely short by using an original single epoch algorithm. It is able to output position and speed data in addition to heading data. In order to confirm the performance and verify the accuracy and availability, many evaluation tests have been carried out in many sea trials in Japan, U.S.A. and Europe over a long period of time. This paper describes the evaluation results also.