To obtain successful results from your survey, several factors must be taken into consideration. The most important is the nature of the ground conditions, especially when there are crops growing on the fields. We have a list of the perfect conditions for geophysics to help you get the most out of your archaeological survey!
So, to begin with, what ground conditions are unsuitable for magnetometer surveys?
The condition of the ground surveyed can affect the result of the survey. If ground conditions are uneven or made of dense materials (such as clay), it can affect the depth of penetration. It can even render underground mapping impossible. SUMO understands that the ‘perfect’ survey conditions will rarely be achievable due to the nature of individual sites. But, we have listed examples of unsuitable ground conditions for geophysical surveys below:
1.Old potatoes fields/ Oilseed rape fields
2. Overgrown sites
3. Potato fields
4. Overgrown, dumped material
So, what are the perfect conditions for magnetometer surveys?
In an ideal world, all survey sites would have the following ground conditions:
2. ‘Stubble’ - short crops after the harvest
3. Lightly ploughed fields
Lightly ploughed fields which have been prepared for crops can be easily surveyed. But, if the plough is deep or the field contains clay soils, then it can become tricky or even impossible to survey.
Are there other factors which affect the carrying out of magnetometer surveys?
Livestock - for safety purposes, livestock should be removed from survey areas.
Agricultural work i.e. certain crop sprays can make fields unsafe for personnel to survey.
SUMO will always discuss the survey area with its clients to understand its current use and to tailor its approach wherever possible.
Most archaeological surveys are carried out using magnetometry, but Ground Penetrating Radar (GPR) is being employed more often. While the same ground conditions apply for GPR as they do for magnetic survey, there are a couple of other issues which need to be considered.
Clay or clayey soils can severely restrict the use of GPR in that the energy waves cannot penetrate through dense soil structure.
A high water-table will also limit the depth of penetration.
Seasonal factors can also affect geophysics surveys both positively and negatively…
The summer months:
Tall crops can interfere with magnetometer sensors. This can make it impossible for the operator to walk safely.
Maize fields are the worst! This is because despite the harvest, the remaining stalks can be extremely brittle. This causes problems for the surveyors walking a site.
It is impossible to collect underground mapping data in potato fields. Other root crops are less of a concern unless the ground is rutted.
The autumn months:
Immediately after harvest is the busiest time of the year for carrying out archaeological surveys. This is because once the crops are gone; clients take advantage of the preferred ground conditions. SUMO would always advise its clients to book surveys as early as possible to ensure your preferred dates.
Why should you use SUMO?
With over 40 years’ experience at the forefront of geophysics, we pride our survey offering on the following:
We employ many of the industry’s leading survey professionals.
All our surveyors are multi-skilled to aid flexibility and tailoring of our services.
Our unique size and nationwide coverage allows us to tailor our service to a client’s individual needs and budget..