Science and Heritage Programme
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Non-invasive methods for in situ assessing and monitoring the vulnerability of rock art monuments

Nottingham Trent University/ English Heritage

Award holder - Dr Haida Liang
Student - Elizabeth Bemand

PROJECT SUMMARY

There are significant numbers of surviving prehistoric open-air rock art monuments, which are exposed to all the extremes of weather conditions. With the increased pollution levels in the last couple of hundred years the rate of decay of these rocks may have accelerated. The most vulnerable parts of the rock art are likely to be the exposed surface and the near surface layers of the rock. If we can monitor small cracks and porosity in subsurface layers on a microscopic scale, we would be able to detect the decay at an early stage and would stand a better chance at stopping or controlling the deterioration. In this project, we will develop a method of using a portable optical coherence tomography (OCT) instrument and a portable magnetic resonance imaging (MRI) device to monitor the microscopic changes in the subsurface layers of rock art panels.  

RESEARCH OBJECTIVES

The aim of the project is to devise a non-invasive method for in situ monitoring of the microscopic changes in rock art monuments to help to assess vulnerability and formulate conservation strategy, and to understand the links between microscopic changes, the environment and long term deterioration. Demonstrate a novel technique and achieve better measurements of porosity of rocks through novel combination of MRI with OCT to monitor surface and subsurface changes on a microscopic scale.

THE MOST IMPORTANT RESEARCH QUESTION

To monitor the condition of these monuments, and changes in their condition, in order to inform and help with the formulation of conservation strategy

RESEARCH METHODOLOGY

Application of MRI and OCT in the laboratory and in the field

EXPECTED OUTCOMES

Demonstrate a method capable of non-invasive in situ monitoring of microscopic condition (porosity, cracks) in rocks which produces a baseline for conservation monitoring of rock art monuments and other porous materials; demonstrate a method for assessing vulnerability of rock art monuments and predict future decay rates in relation to environmental variables; Train a physicist at PhD level with experience in multidisciplinary/interdisciplinary approach to problem solving and understanding of conservation needs.

SOCIAL, ECONOMIC AND ENVIRONMENTAL IMPACTS

Results from the research can potentially result in better protection of cultural heritage and greater savings in the cost of conservation monitoring.

RESEARCH SUPERVISORS

Nottingham Trent University: Dr Haida Liang, Dr Martin Bencsik, Professor Brian Pyatt; English Heritage: Dr. Sebastian Payne

ABOUT ELIZABETH BEMAND

Rock art panel, Chatton Park, Northumberland. Image © B Kerr


Elizabeth Bemand completed an MSci in Earth Science at Royal Holloway, University of London in 2002, followed by a PGCE in Secondary Science, specialising in Geology, at Keele University. She subsequently worked as a High School Science and Geography teacher.

The aim of Elizabeth’s project is to develop non-invasive methods for assessing subsurface conditions likely to correlate with vulnerability (e.g. porosity) and to open a new area of research whereby the novel combination of two non-invasive techniques (OCT & MRI) is applied for the first time on rock art monuments. Weathering causes progressive changes in rock porosity. Previous studies investigating porosity have been dependent on sampling and as such are not suitable for repeatable monitoring or culturally important materials.

Magnetic Resonance Imaging (MRI) is a non-invasive imaging technique which relies on the detection of the spatially resolved NMR signal from a hydrogen containing fluid (e.g. water). It can be used to investigate the presence of water in porous media. This project’s method uses a portable MRI device, the Mobile Universal Surface Explorer (NMR-MOUSE®) which allows scanning of samples placed outside the instrument. The NMR can provide depth profiles up to 10mm into the surface and measure the porosity in fluid saturated samples. Such devices are used extensively in the oil industry for well logging, but have recently also been shown to be suitable for cultural heritage applications.

Optical coherence tomography (OCT) is a fast scanning near infrared Michelson interferometer capable of measuring the surface profile and subsurface structure of materials. It registers the back-scattered light from the surface and subsurface layers. Preliminary studies show that it can also directly image the pores and subsurface structure of rocks. 

A third instrument is proposed to enable large area scanning of rock surfaces. PRISMS (Portable Remote Imaging System for Multispectral Scanning) is a system designed for in situ, remote hyperspectral imaging. It is a non-invasive technique capable of recording the spectral reflectance per pixel for millions of points simultaneously. The reflectance at water absorption bands in the near infrared can be used to monitor the relative water content in the surface and subsurface of porous media, providing an indication of the effective porosity. 

These instruments can be used to monitor the surface and subsurface structure on a microscopic scale on selected regions. By monitoring the changes in the surface and porosity in the subsurface layers we may be able to detect decay at an early stage informing conservation decisions.

LINKS AND CONTACT DETAILS

Rock art panel, Chatton Park Northumberland. Image © B.Kerr

Rock art panel, Chatton Park Northumberland. Image © B.Kerr


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