Mean-square error due to gradiometer field measuring devices

It is pointed out that unless the gradiometer baseline is at least several times the source depth significant error will result from any attempt at detailed analysis of the magnetic fields arising from current sources of interest. Although many investigators have been impressed with the effectiveness of spatial mode rejection, the data collected have been in many cases severely distorted. Attempts to correct these errors through decorrelation using the inverse transform of 1/T( alpha , beta ) will not be possible because its inverse does not exist, and because it is a highpass function its use in an inverse transform technique will emphasize high spatial frequency noise components. It is concluded that the goals of a design for a facility for measuring biomagnetic fields should be an effective shielded room and a field detector employing a first-order gradiometer.