Resistivity surveys are conducted using Geoscan’s RM15 Resistance Meter, a standard twin probe mobile array, and two fixed remote probes.  The meter consists of a constant current source transmitter and high input impedance receiver.  This virtually eliminates errors due to contact resistance between the probes and the ground, and current ranges allow readings to be taken even in dry conditions.  The mobile probes are fixed at 0.5m separation, and readings are normally taken at 1m in both the x and y axes, although detailed surveys at 0.5m pitch in the y axis can be undertaken on request. 

Resistivity surveys are particularly useful in indicating shallow (on average up to 0.75m) buried archaeological features.  They are often more effective than gradiometry for detecting stone buildings or floors and in many circumstances will detect ditches and substantial pits.  Initial filtration is applied at the data input stage to mitigate the “noisy” effects of residual mains electrical earth currents and local geological variation. 

For processing data, GeoFlo use Geoscan’s Geoplot 4.0, which supports statistical analysis and filtering of the data.  When processing resistivity data, isolated high or low readings (noise spikes sometimes caused by a false contact) can be replaced by the mean reading.  The technique is particularly susceptible to geological variations which may be reduced by the application of a uniform high pass filter.  Weak anomalies may be highlighted by the application of a gaussian low pass filter and the data smoothed by interpolation.