Abstract: Electromagnetic exploration methods are used to identify a subsurface anomalous feature. This is sometimes difficult in the presence of large fields from the transmitter or other surrounding material that may be above and around the subsurface feature. By constructing linear combinations of the field and gradients of the field it is possible to remove the large fields associated with the transmitter and the surrounding material to make identification of the anomalous subsurface material easier. The fields and gradients can also be combined so as to provide estimates of other electromagnetic field quantities that would be otherwise difficult to measure, for example the electric field or the time derivative of the electric field.