Portable, hand-held gamma-ray spectrometers are widely used in mineral exploration and environmental studies. However, for mapping applications vehicle-borne surveys are more commonly employed. The gamma-ray detectors are mounted on a motor vehicle or quad-bike for continuous recording as the survey area is traversed (Figure 5). The gamma-ray detectors are usually airborne detectors modified for use from a vehicle. Otherwise the acquisition, navigation and processing of the data is essentially the same.
A big advantage of ground-based surveys is that the background component of radiation is much smaller (as a fraction of the signal) than for airborne surveys. Consequently a much simpler background correction can be applied to ground-based data. The greatest disadvantage of ground-based surveys is that the measurements are very much affected by the topography - even in moderate terrain. Any variations from a "flat-earth" affect the accuracy of the final measurements. Road cuttings, boulders, buildings and undulating terrain all affect the accuracy of ground-based measurements.
Figure 5 (left). Quad bike fitted with a 4 litre crystal pack (red box between handle bars), differential GPS and EM31 conductivity meter (white pole). The system is used to acquire high resolution gamma-ray imagery and near-surface electromegnetic conductivity (see Figure 24).