Large-area high-resolution ground-penetrating radar measurements for archaeological prospection

Traditionally, ground-penetrating radar (GPR) measurements for near-surface geophysical archaeological prospection are conducted with single-channel systems using GPR antennae mounted in a cart similar to a pushchair, or towed like a sledge behind the operator. The spatial data sampling of such GPR devices for the non-invasive detection and investigation of buried cultural heritage was, with very few exceptions, at best 25 cm in cross-line direction of the measurement. With two or three persons participating in the fieldwork, coverage rates between a quarter hectare and half a hectare per day are common, while frequently considerably smaller survey areas at often coarse measurement spacing have been reported. Over the past years, the advent of novel multi-channel GPR antenna array systems has permitted an enormous increase in survey efficiency and spatial sampling resolution. Using GPR antenna arrays with up to 16 channels operating in parallel, in combination with automatic positioning solutions based on real-time kinematic global navigation satellite systems or robotic total-stations, it has become possible to map several hectares per day with as little as 8 cm cross-line and 4 cm in-line GPR trace spacing. While this dramatic increase in coverage rate has a positive effect on the reduction of costs of GPR surveys, and thus its more widespread use in archaeology, the increased spatial sampling for the first time allows for the high-resolution imaging of relatively small archaeological structures, such as for example 25 cm wide post-holes of Iron Age buildings or the brick pillars of Roman floor heating systems, permitting much improved archaeological interpretations of the collected data. We present the state-of-the-art in large-scale high-resolution archaeological GPR prospection, covering hardware and software technology and fieldwork methodology as well as the closely related issues of processing and interpretation of the huge data sets. Application examples from selected European archaeological sites illustrate the progress made.