Archaeological Survey In The Gyanvapi Mosque
The Supreme Court of India directed the Archaeological Survey of India (ASI) to conduct a detailed non-invasive survey of the Gyanvapi mosque in Varanasi, Uttar Pradesh to determine if the mosque was built atop a temple.
Since the investigation is being undertaken inside a built structure, and no excavation is permitted, experts — geophysicists in particular — must depend on non-invasive methods of earth-scanning.
The methods routinely used in archaeological prospecting are adapted from those applied in geophysical mapping. They may be active or passive.
Active methods inject energy into the ground and measure the response of the buried target at the surface.
They include seismic and electromagnetic techniques.
Passive methods, such as magnetometry and gravity surveying, simply measure existing physical properties.
In both cases, the methods provide an estimate of the ground’s material properties, such as density, electrical resistance, and wave velocity.
They are then interpreted in terms of the possible nature and geometry of the target.
In the case of Gyanvapi, the scientists could be looking for the distinct physical properties of subsurface material constituting the structure.
Geophysicists use multiple methods and different physical properties of the earth’s materials to arrive at a reasonable characterisation of the target.
ASI will use ground-penetrating radar (GPR) to produce a 3-D model of buried archaeological features.
Challenges
Many earth materials could have the same physical property and generate the same response on the surface, leading to ambiguity in interpretation.
An important aspect of the geophysical survey is to infer physical parameters from the complex and voluminous data acquired.
This requires a good understanding of physical processes and powerful data analyses and modelling programs to generate reliable 3D images.
The archaeological object under investigation is made of heterogeneous materials with complex geometry.
As the data will always be limited and have measurement errors, it may not be possible to estimate, in a unique and stable manner, the spatial distribution of physical property in the subsurface.
As a result, supplementary information needs to be incorporated. This has the potential to produce meaningless results.
Despite its inability to reconstruct the images of targets in the best possible manner, geophysical tools have a high success rate in resource exploration.
Here, ‘temple versus mosque’ problem is another matter entirely, involving emotional and sentimental issues and with long-term societal and political implications.
In such cases, nothing should be left to chance.
GPR or any other geophysical method has limited abilities, and its findings must be interpreted within these contours.
During data analysis, interpreting, and decision-making, experts as well as the people need to bear this in mind.
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