ImagingOur geophysical instruments are GPS synchronized for rapid data acquisition and images are immediately generated in-field.
GPS synchronized geophysical data are imported into a Geographic Information System (GIS). GIS software allows the information to be georeferenced and graphed. Gridding algorithms interpolate levels between sample points to produce an image. Measurements are expressed as a scale of intuitive hot and cold colours. The colour white is used for low-end responses that represent background (i.e. naturally occurring) values.
Maps are projected in Universal Transverse Mercator (UTM), so that distances are expressed in meters. These features make the maps easy to interpret and georeferencing allows for instant positioning on mobile devices. Site features are surveyed, drafted and included as an overlay on all maps. We also overlay sample points and walking lines to facilitate interpretation. Electromagnetic responses depend greatly on the orientation of the instrument with respect to the anomaly, in cases of buried metals and pipelines. This is important for another reason: sample density is a major factor in the gridding algorithms that determine image quality.
Nyquist's Sampling Theorem dictates that to completely capture any given frequency in an analog signal, discrete measurements must sample at double that frequency to retain signal fidelity. An audio wave file, for instance, samples at 40 kHz which is twice the maximum frequency discernible by the human ear. In imaging, the theorem applies to spatial frequencies. This implies that resolution of an anomalous trend twenty meters wide requires walking lines no more than ten meters apart.
The theorem also limits the maximum resolution of any particular geophysical instrument. For example, an instrument with a footprint 6.5 meters wide (like the EM31) may not detect features smaller than thirteen meters.