Positioning Electric Field Sensors in the Marine Environment Using Passage Data

Sammanfattning: When underwater sensors are being deployed there is always some uncertainty about the actual position of the sensors. The most common way of determine the sensors position is the use of hydro-acoustic methods. However, for electric field sensors the most favourable would be to use the sensor system itself. The first question being answered in this report is whether it is possible to position electric field sensors with the sensor system itself, and the answer is yes. An algorithm has been developed which calculates the relative position of the sensors based on data measured by the sensors when a dipole passes the sensor group. The algorithm extracts zero crossings of the z-components of the electric field measured by each sensor from the data, which are converted to moments in time, multiplied by the speed and course of the vessel and finally calculated into relative position vectors between the sensors using vector algebra. The result of the predicted relative position is within 0.2 m from the sensors’ actual position, which answers the second question about how accurate the method is. However, the error estimation is within a couple of centimetres indicating that there are other sources of error than speed and course. The third question being answered is whether the method is better than acoustic methods, and the answer is no. Nonetheless, the methods are within the same order of magnitude. In conclusion, the method has acceptable performance, especially considering the fact that it can determine the position of the sensors with the sensor system itself which could be significant.