A scientific survey at Gyanvapi, its limits
Context:
Recently, the Supreme Court (SC) of India directed the Archaeological Survey of India (ASI) to conduct a detailed non-invasive survey of the Gyanvapi mosque in Varanasi. As all scientific techniques have limitations, must be kept in mind while settling a dispute with such significant political implications needs a directive.
Technique to be used by ASI:
- Ground-penetrating radar (GPR) technique: It will be used to produce a 3-D model of buried archaeological features by introducing a short radar impulse from a surface antenna and recording both the time and magnitude of return signals reflected by the property contrasts in the subsoil.
- Seismic and electromagnetic techniques: These are active methods inject energy into the ground and measure the response of the buried target at the surface. They include seismic and electromagnetic
- Measuring physical properties: There are some passive methods, such as magnetometry and gravity surveying, simply measure existing physical properties.
Challenges with these techniques in ‘Gyanvapi’ case:
- Dependence on Non-invasive data: Archaeological investigations are normally performed in open spaces, along with excavation, whereas in the present case, the investigation is being undertaken inside a built structure, and no excavation is permitted.
- Difficulty in identification of distinct physical properties: The methods being used provide an estimate like density, electrical resistance, and wave velocity to get nature and geometry. However many earth materials could have the same physical property and generate the same response on the surface, leading to ambiguity in interpretation.
- May get false images: As a part of the signal may bear little relation to the physical dimensions of the subsurface target, it may create false images.
Points to be taken care of:
- Need of supplementary Data: As the data will always be limited and have measurement errors, it may not be possible to estimate the spatial distribution of physical property in the subsurface. As a result, supplementary information needs to be incorporated.
- To consider financial loss: Despite its inability of geophysical tools to reconstruct the images of targets in the best possible manner, they have a high success rate in resource exploration. But in the case of a failure or partial success, the loss is merely financial.
- Scientific Techniques have limited abilities: GPR or any other geophysical method has limited abilities, and its findings must be interpreted within these contours.