I asked a while ago about this, and have just received this response (below), which may be of interest
We're not aware of any systematic studies but from experience masking of anomalies in magnetometer surveys (the enquirer doesn't specify the technique but this is the most commonly used) can occur in some situations although it depends very much on local geological and topographical conditions. Broadly speaking we have encountered three types of situation WRT ridge and furrow responses:
1) Where the topsoil magnetic susceptibility is high in comparison to the magnetic susceptibility of more deeply buried archaeological features the latter can be obscured and not be detected. We encountered this at Whitby Abbey<http://research.historicengland.org.uk/Report.aspx?i=14581&ru=%2fResults.aspx%3fp%3d1%26n%3d10%26t%3dwhitby%26ns%3d1 > where strong responses to surface ridge and furrow masked archaeological remains which were demonstrated to be present by later excavation.
2) Where topsoil and subsurface magnetic susceptibility are similar, the magnetic responses of the more deeply buried archaeology are superimposed on the ridge and furrow response and the latter can be revealed after processing the data using a de-corrugation or directional cosine filter. We encountered this at Nuneham Courtenay<http://research.historicengland.org.uk/Results.aspx?p=1&n=10&t=nuneham&ns=1> (sorry the A1 plans seem not to have been scanned for these reports).
3) However, the ridge and furrow can, of course, be truncating the earlier archaeology which can give a geophysical response similar to 2) but, on excavation, the strongest geophysical anomalies can be found to be badly truncated by the furrows their strong response being due to the lack of any topsoil overburden. We encountered at Kellaways Farm<http://research.historicengland.org.uk/Report.aspx?i=15391&ru=%2fResults.aspx%3fp%3d1%26n%3d10%26t%3dkellaways%26ns%3d1 > where excavation of the very clear magnetic anomalies revealed they had been severely truncated with little fill left.
Earth resistance survey can also exhibit similar responses but in this case depending on ground water conditions at the time of survey. Given the enquirer's description of the results, 1) is the case likely to be of concern but it is not possible to assess further without more knowledge of the site conditions and survey methodology. However, in general, more certainty could be gained by re-surveying at least a test area with a 2nd geophysical technique (e.g. earth resistance if the initial survey is magnetic). It may also be possible to get an idea of the response for a particular region by searching for surveys with Monument Type "ridge and furrow" on the Geophysical Survey Database: http://archaeologydataservice.ac.uk/archives/view/ehgsdb_eh_2011/
Historic Environment Record Officer
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