Geophysical Survey in Archaeological Field Evaluation - HELM

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Page numbers in the right hand column refer
to pages elsewhere in the document where
more detailed discussion is available: readers
are cautioned not to accept a survey option
without consulting the relevant sections of
Part IV. The same advice applies to Table 3,
which lists some of the most commonly
occurring types of archaeological feature, and,
alongside each, attempts to categorise the
suitability of the main survey techniques for
its detection in each case. Table 4 lists very
generalised comments on the suitability of the
major solid and drift geologies to magnetometer
survey only (the responses of other geophysical
techniques to differing geologies are less easy
to categorise simply; where possible reference
to these responses is made independently in
Part IV).
In submitting these tables we must acknowledge
that they are a considerable over-simplification
and therefore reiterate that they are intended
to serve only as a rough guide to choice of
survey technique. Professional opinion varies
on some of the attributions offered. For the
moment, and into the foreseeable future, each
situation will warrant specialist advice and this
should be sought at an early stage in any project,
once the general necessity for geophysical
survey has been established.
The tables are followed by a more specific
discussion of the survey options for a selection
of commonly occurring evaluation scenarios.
For those who wish to follow up aspects of
technique and methodology in more detail we
recommend consulting Part IV. Furthermore,
valuable complementary information is available
in the following publications: Clark (1996);
Gaffney and Gater (1993; 2003); Gaffney,
Gater and Ovenden (2002); Linford (2006).
3 Costs
Routine archaeological surveys are usually
costed per hectare of area covered at standard
sampling intervals. Such prices are usually
inclusive of all aspects of the work and the
supply of a report (and a specified number
of copies of this). However, in some cases –
particularly geotechnical surveys – quotations
may not be all-inclusive and fieldwork may
be costed per day on site with separate
charges for data analysis and reporting. There
may be a reduction if multiple techniques are
carried out on a shared grid and concessions
may be available if there is a research and/or
publicity interest for the company concerned.
Prices can vary significantly between different
companies and will of course vary according
to constraints peculiar to each site. Clients
are advised to obtain a range of quotations
for scrutiny. Care should be taken to
establish whether or not VAT is included.
On completion of the tendering process it is
good procurement practice for the client to
name the successful contractor, to declare the
range of prices received and to provide a list
of tender applicants.
4 Urban (and brownfield) sites
The depth and complexity of most urban
stratigraphy, closely constrained by modern
intrusions, metallic contamination, services and
adjacent structures, provides a near insuperable
Table 3 Matching survey method to feature type: survey options (see key below): the choice
of geophysical survey method(s) appropriate to a range of archaeological features, based on
experience from the UK. Only the most commonly used survey methods are listed. This is a
rough guide only, to which there will be exceptions, depending upon individual site circumstances
and future technical developments.
Feature type Mag area Earth res GPR EM Mag susc
survey survey (cond)
areas of occupation Y n N ? y
below artefact scatters Y Y N ? y
large pits (>2m diam) Y y Y ? N
smaller pits (0.5m diam) y n y N N
hearths Y N N n ?
kilns/furnaces Y N ? ? ?
sunken-featured buildings Y y ? ? N
house platforms ? y n ? ?
ditches (2m width) Y y ? ? n
palaeochannels y y Y y n
roads/tracks y y ? ? n
robber/bedding trenches y Y ? N N
timber structures y n ? N N
masonry foundations ? Y Y Y N
brick foundations y Y Y ? N
paving/floors – Y Y ? N
buried megaliths (mag) Y Y Y ? N
buried megaliths (non-mag) – Y Y ? N
stone-lined drains n y Y ? N
other cavities n Y Y ? N
graves ? y ? N N
cremations n N N N ?
ridge and furrow Y Y N n n
lynchets y Y N n n
waterlogged contexts ? ? ? ? ?
key:
Y The technique responds well in many conditions and is usually to be recommended.
y The technique can respond effectively in many conditions but is best used in conjunction
with other techniques.
? The technique may work well in some conditions, and its use may therefore be
questionable; another technique might be preferable.
n The technique may work in some conditions but is not usually recommended; another
technique is usually preferable.
N The technique is probably not effective, or its effectiveness is uncertain.