Exploitative Properties of Different Types of Satellite Compasses

Satellite compass is the specific, multiantenna receiver of the satellite navigation system which, apart from the standard functions, like position, time, Course and Velocity etc. enable to measure the angles of the orientation of the ship's hull. The most popular solution is two-antenna solution, which gives opportunity to measure two angles: heading and pitch or roll. However, three antenna solutions are accessible as well (www.furuno.co.jp). In this option the device can measure full information about space orientation of the object. Discussed devices has common name 'compass' although they are still not officially confirmed in this role and according IMO's resolutions they can be used only as auxiliary source of information and is classified as Heading Transmitting Devices (MSC.116). The origin of satellite compasses we can find in interferometry used in astronomy since sixties, however the present solutions in fact are adopted from Real Time Kinematic variant of GPS technology (Felski 1999). Nonetheless products accessible on the shelf are very diverse in construction, electronics and software so in practice of their exploitation very different proprieties could be observed. In the report the practical experiences with the use of two different types of satellite compasses are presented, as well as the analysis of observed errors. It turned out that the behavior of satellite compass is not comparable to any gyro or magnetic compasses which are in fact something natural. In fact signal from satellite compass has three kinds of errors: first one is small noise with amplitude of same arc-minutes which is natural in any electronic devices, the second one is long-term changes which are seems be dependent on satellite constellation configuration and finally short, big changes correlated with transition period when new configuration of satellites is catches-on. According to the observations very important are solutions assumed in electronics and software, because observations confirm that two different constructions characterize themselves with very different proprieties.