The use of GPS for determining a true north bearing for measurement of magnetic declination

When two GPS receivers are placed some distance apart and positional data are logged simultaneously using the same satellite combinations errors common to both receivers are eliminated and it is thus possible to obtain very accurate relative positional accuracy. This technique of differential GPS processing allows computation of an accurate true bearing between the two receivers. If the bearing of one receiver position from the other is then used as an azimuth reference then a true bearing for magnetic declination (D) measurements is obtained. This technique is examined using different types of GPS receivers, ranging in sophistication, practicality and price, from survey grade receivers to basic handheld units. The use of GPS networks is also examined which enable measurement of true bearing using only one receiver.