North Hoyle Windfarm Report

2 QinetiQ GPS trials

2.1 Overview

The number of satellites visible to a GPS system bears a direct relation to the accuracy of the positioning. For the GPS system to work there must be line-of-site to at least four satellites. At any one time the GPS units can usually receive signals from up to twelve satellites. The more satellites that can be used in a positioning measurement, the more accurate the estimated position will be. The original theoretical study [1] demonstrated that it is unlikely that any electromagnetic interference will effect the normal operation of GPS system, unless the receiver is in very close proximity to a turbine tower.

The GPS trials consisted of piloting a launch along three predefined courses. Two control runs, away from the wind farm were also made. On each course the number of satellites used by the GPS receiver was recorded along with position. Two GPS systems were used, a Garmin GPSIII and a Garmin GPS152. The first is a typical hand-held GPS receiver and the second is typical of what might be found installed on small ships, launches and pleasure craft.

Full details of the experimental methods for the GPS trials can be found in the trial plan [2].

The antenna for the GPS152 was positioned on the cabin roof as illustrated in Figure 2-1. The hand-held GPSIII unit was positioned at the centre of the rear deck of the vessel.

Figure 2-1: The position of the antenna for the Garmin GPS152 unit