Does the GPS affect the EM sensor in a manual survey?
A. When a survey is conducted manually, not only is the operator placed between the coils of the EM sensor, but also the GPS backpack, which includes the receiver, battery, antenna, range pole and data collector. All of these components, including the operator may have an effect on the coils of the sensor, which is generally a non-linear, positive bias. The effect of this bias is to some extent specific to the type of EM sensor being used. The Geophex GEM2 appears to be affected the most, due to its relatively short (1.6 m) coil spacing and the multiple frequencies, which will always be affected by the GPS. The EM31 appears to be affected the least, most likely because of its relatively wide coil spacing (3.8 m). AN EM 38 may be affected by the GPS depending on the height of the operator. With a short person, the GPS backpack will be within the ellipse of EM radiation, but with a taller person, the GPS may be outside of the 1.5 m ellipse of radiation. GPS effects may be manageable, but
