Installation of Van Walt Soil Moisture Sensors 1st August 2011
On the 1st August 2011, the Van Walt soil moisture sensors were installed at Diddington in the clay field. Yvonne Coonan and Vincent Van Walt, from Van Walt Ltd, Dan Boddice and Alex, from Birmingham University, and Anthony Beck, from University of Leeds, were all in attendance.
Keith Wilkinson, from Winchester University, had already set out the trench location and proposed boreholes using Differential GPS. There was some latitude in location outside the archaeology as long as it was installed along the same vector. The external probe was installed some 3m away from the archaeology probe.
Essentially installation required the following actions:
- Producing a borehole with a corer
- Inserting the installation sleeve (made of non-porous plastic material) – this has a snug fit with the borehole
- Ensuring the sleeve is clear of sediment
- Installation of a water-tight seal at the bottom of the tube
- Insertion of the Soil Moisture Sensor tubes
- Connecting cables to the logger and telemetry system
- Sealing the units, protecting and burying the cables.
With the aid of the estate we marked the area with fence posts so that it would not be inadvertently damaged by any agricultural process.
A video has been produced of the installation process:
The sensor tubes themselves consist of three 110mm sensors. These sensors send out pulses that take readings from a c. 150mm radius. The position of these sensors is configurable.
The sensors still need calibrating. This will be done during the installation of the Birmingham sensors on the week commencing the 25th August. As the deposits are exposed Dan and Vincent will take calibration measurements based upon the specific soil types of the sediments. Specific calibration curves will then be applied to the sensors. Whilst it is appreciated that the callibration measurements are not taken using the exact soil in which the probes are installed, the probes are installed some 3m away from the proposed trench, they should share the same formation processes and macro properties.
In the archaeology: probes 32316, 32318, 32354 are measuring at 10-21, 40-51 and 70-81cm respectively. In the ‘natural’ profile: probes 32145, 32245 and 32639 at the same levels.
Many thanks to Vincent and Yvonne for being supportive, providing such clear information and for loaning the DART project one of the sensor tubes!