At Perdigões two methods of geophysics were tested. First georadar. Slower and needing a considerable cleaned soil (for the radar runs a few inches over the surface), this method was totally disappointing.
Georadar image of the center of Perdigões enclosures
On the contrary, magnetometry, not just is faster in the measurements, but provided excellent results. In Perdigões, but also in Xancra, Moreiros 2, Monte do Olival 1, Luz 20, Montoito, Monte da Contenda, images that you can see all through this blog. Or you can search in the net for tens of European examples.
Image of the same area done by magnetometry
For negative structures, like pits and ditches, magnetometry is the method that provides best results. Of course the quality depends of several circumstances (like the bedrock or the proximity of highly magnetic material) that need to be taken into consideration. But the results leave no doubt.