Ideas on Geophysical Methodology (V2)
Notes on the DART Geophysical Survey Methodology
It strikes me that the current project methodology (FieldAndLabMethodology.doc) is very brief on the subject of the geophysical fieldwork to be undertaken over next year, with just a vague mention that ‘similar evaluation scenarios will be adopted for the geophysical surveys’. I would therefore like to start a methodology for the geophysical detection of the archaeological features over the next year.
Preliminary survey over the test areas:
Fluxgate gradiometer (Bartington 601-2 or Geoscan FM – Bradford University) survey to be performed over the sites at a fine resolution (0.125m x 0.25m) to ensure there is a good magnetic data-set to compare findings to. This will detect the major archaeological features, as well as magnetically ‘quiet’ areas.
A full resistance survey (Twin-Probe / Geoscan MSP40 – Bradford University) should also be undertaken at high resolution (about 0.5m x 0.5m if possible).
GPR survey – I believe Birmingham might have a good GPR that can be used (?), if not Bradford do have an adequate system. A full area survey with GPR would help identify depths and the structure of archaeological features in greater detail.
The areas targeted for monthly surveying will be either within the area of the in-situ sensors, or directly adjacent to them (as the ground where the sensors are placed will be disturbed). It is envisaged that high-resolution surveys will take place within an area of a 10m grid. This is specifically set to limit the impact on the agriculture to the landowner, but should be ideal in order to assure targeted and focused fieldwork. A section of topsoil will also be stripped during the excavation for the in-situ sensors to investigate the effects of the topsoil on archaeological detection.
The fluxgate gradiometer survey shouldn’t (in theory) need to be undertaken every month as the magnetic data is not expected to change significantly…however, it might be interesting to maybe conduct a survey every month, just to check the magnetic changes throughout the year. This could indicate variations to do with land formation over the period, how the initial disturbance of digging, inserting probes and invasive investigation has affected the magnetic response, and how our actions over the year affect the response. This is something I would like to test; especially as the time it takes to survey would be minimal compared to the resistance surveying. The results could be surprising.
Area resistance survey (TwinProbe / Wenner / MSP40)to be conducted over the sites once a month, within a certain threshold period of the hyper-spectral flights having taken place – ideally as soon as possible. This data will be then compared to the hyper spectral datasets for analysis into the ARs which present themselves. Analysis of the data against seasonality will also take place each month.
Depending on the ERT equipment bought (which as I understand it, depends on the outcome of the NERC funding) survey will be performed once a month (and repeated throughout the day?) to assess the different ground conditions along the pseudosection which can be compared to the soil data collected by the in-situ probes. If DART is able to acquire the FlashRes64 (on the understanding that NERC will fund flights) then multiple resistivity imaging arrays can take place over the day (time permitting). Again, it would be ideal to have this fieldwork taking place within a certain time frame of the flights having been conducted and the resistance data-sets surveyed. We will, from this equipment have data responses from many different probe arrays which can be compared, and integrated with each other. Chris and I are currently in talks with Allied Associates concerning this.
GPR profiles will also be taken to have a direct comparison between the ERT data and soil conditions. Area survey with GPR might also be an option to compare to the resistance survey and hyper-spectral flights also. It may only be necessary to conduct sample set of traverses over the archaeological feature, however, due to such a small area (10m square), a full GPR survey can probably be conducted. (Resolutions will have to be decided).
This is just a starting point and aimed to stimulate discussion on the subject of the geophysical methodology. Comments welcome.