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Above: A close-up picture of the ‘Blue Stones’ of Stonehenge. Headed up by Adam Stanford, SUMO’s Director of Aerial Survey, Aerial-Cam Limited provides a specialist geospatial imaging service employing the latest techniques, equipment and software to produce high quality evidence photography, photogrammetry and multispectral imaging, recording features and evidence in archaeological excavations, topography and earthworks of landscapes and ancient monuments. Also surveying historic buildings to produce 3D models, rectified orthomosaic elevations, plans and roof details. Above: Processed data captured from a UAV. Above: 3D image model. Adam is a Member of the Chartered Institute for Archaeologists, the Council for British Archaeology and a Fellow of the Society of Antiquaries. With expertise in photography, archaeological field work and surveying experience spanning three decades, Adam has been involved with the Stones of Stonehenge and related projects for 15 years. Adam’s work can now also be seen in a new documentary ‘Stonehenge: The Lost Circle Revealed’ on BBC2: In the programme, Professor Alice Roberts follows a decade-long historical quest to reveal a hidden secret of the famous bluestones of Stonehenge. Using cutting-edge research, a dedicated team of archaeologists led by Professor Mike Parker Pearson of the Institute of Archaeology, University College London, have painstakingly compiled evidence to fill in a 400-year gap in our knowledge of the bluestones, and to show that the original stones of Britain’s most iconic monument had a previous life. Together they join the final pieces of the puzzle, not just revealing where the stones came from, how they were moved from Wales to England or even who dragged them all the way, but also solving one of the toughest challenges that archaeologists face. For anyone interested in Stonehenge or archaeology generally, the programme makes a fascinating watch.

Crops, clay & clutter and how they affect your archaeological survey. Geological and buried manmade features or objects can cause local variations in the earth’s magnetic field, which can be measured with a magnetometer. Accordingly, a detailed magnetic survey can be used to effectively define areas of past human activity and it is a quick, cost effective technique. As such, it has become the industry standard for archaeological surveys. However to obtain successful results from your archaeological (magnetometer) survey, several factors must first 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 therefore set out below, a list of the perfect conditions for geophysics to help you get the most out of your archaeological survey. In an ideal world, all survey sites would have the following ground conditions: - 1. Short pasture, or early season crops 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. So, what ground conditions are unsuitable for archaeological surveys? Factors affecting the magnetic survey may include soil type, local geology, previous human activity, disturbance from modern services etc. The physical state of the ground itself can also significantly affect the result of the survey, especially rough or uneven surfaces. 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 archaeological surveys below: 1. Old potatoes fields/ Oilseed rape fields 2. Overgrown sites 3. Potato fields 4. Untidy, dumped material 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. Example magnetic survey equipment which can either be towed by a quad bike (where conditions allow) enabling large amounts of data to be collected quickly, or man powered, which is somewhat slower! Smaller two sensor arrays which can be carried by an individual are also used in less open sites. 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. Above: Ground Penetrating Radar (GPR) equipment. Seasonal factors can also affect geophysics surveys both positively and negatively… The spring months: Early spring is an ideal time for a survey, when the weather is improving and the land is drier, but before the crops have grown significantly. New crops can be delicate and severely impacted by either cart systems or trampling under foot which can result in the landowner being unwilling to authorise a survey until the crop has matured or even been harvested. 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 the site. It is impossible to collect underground GPR mapping data in potato fields. Other root crops are less of a concern unless the ground is heavily rutted. The summer is also an ideal time for aerial surveys, when archaeological features can often be seen as a result of the differing moisture contents between archaeological remains and the surrounding land. The autumn months: Immediately after harvest is a perfect time for a survey, when the land is dry and the weather is good. The busiest times of year for carrying out archaeological surveys are therefore spring and autumn, when clients can take advantage of the preferred ground conditions. As such, SUMO would always advise its clients to book surveys as early as possible at these times to ensure their 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. So, beat the rush, get your order in early and don’t let your competitors get that all important survey slot!

Sinkholes have been appearing throughout Britain at an alarming rate in recent years. Following heavy rainfall, the ground becomes saturated and as the water levels recede, they can wash out material, leaving substantial life-threatening voids to appear without warning. Some rock types are more susceptible to the formation of sink holes, with carbonate rocks including chalk and limestone being particularly sensitive, as they can be easily dissolved by groundwater. Furthermore, if the rock is overlain by clay material, this forms a configuration that can produce a large void that suddenly collapses when the clay layer above fails. Less dramatic sinkholes also occur where the overlying material is more porous and slowly ingresses into the underlying void resulting in a gradually deepening depression over time. With chalk prevalent in England’s South Eastern counties, along with areas of limestone in Wales and Northern England, the impact of sinkholes can be significant, both in terms of risk to life and financial cost. So, if a sinkhole suddenly appears, or you have an unexplained depression on your site, you urgently need to know the extent of the problem, its likely cause and the risk of more incidents. Thankfully, SUMO has the answer to this problem: SUMO Geophysics can complete a full geophysical survey of the area, using ground conductivity and/or ground penetrating radar. Electromagnetic ground conductivity surveys measure ground conductivity by the process of electromagnetic induction. A current is induced into the ground to generate a response from the sub-surface. This is done utilising a transmitter and receiver coil spaced at a fixed configuration, with different operating frequencies providing a range of depth penetration and resolution for different applications and can be used to identify anomalous features underground, such as saturated ground and landfill. The EM31, a particular ground conductivity system, operates at an intermediate frequency and is ideal for locating discrete features such as sinkholes. Above: Ground Conductivity Survey to locate sinkholes using a Geonics EM31. The data is digitally recorded on site for later post-survey processing and interpretation. The data is processed with specialist software to produce contour plans. The contoured data is then analysed in detail to identify anomalous features relative to the general background and once identified, the anomalies are correlated with local ground conditions. Survey results are then presented as plans tied in to site or OS co-ordinates, in AutoCAD and PDF format. The example below shows the results of the ground conductivity survey, following the appearance of a hole in the middle of a school playing field. The survey identified a notable high conductivity anomaly, which has been interpreted as occurring where saturated gravels are present over the underlying chalk stratum. It is likely that groundwater within the gravels has seeped down to the chalk and is generating the formation of solution features. Furthermore, as this groundwater flow in the gravels is likely to continue, then further solution features are likely to occur and with them, further sinkholes. Ground Penetrating Radar (GPR) surveys work by pulsing electromagnetic waves into the ground and measuring the strength and time delay of the returning signal, which also allows it to approximate the depth of the underground anomaly identified.It has capacity to work through a wide variety of surface materials, from soft landscaping, through to hard surfaces such as tarmac and concrete both inside and outside buildings. Above: GPR survey using GSSI Radar system and 400MHz antenna. The data is collected along set grid spacing and displayed as a section view or profile of the ground. Large or obvious anomalies may be interpreted on site, but the data is typically analysed and processed in the office after the survey is completed. Each radar profile is abstracted and significant anomalies are classified. This is the primary source for producing the 2D interpretation plot. Above: Example radar data showing area and depth of anomaly likely to be voiding below the ground. In addition to a manual abstraction, a computer analysis is carried out. The radar data is interrogated for areas of high activity and the results presented in a plan format known as timeslice plots using GPR Slice software. In this way it is easy to determine if the high activity areas form recognisable patterns. Above: GPR timeslice plot showing the location of possible voids. Conclusion: The use of a combined geophysics survey can not only identify the depth and location of an underground anomaly, but with expert interpretation, may also identify the likely cause of a sinkhole or unexplained ground depression, together with the potential risk of more such incidents occurring. As such, given both the risk to life and the financial cost that such anomalies present, the low cost option of a geophysics survey is an excellent solution to mitigating such risks.