Non-Invasive Archaeological Survey at Gyanvapi Mosque

Source: The Economic Times

Why in News?

Recently, 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.

What is the Purpose of the Survey?

The petitioners argued that the mosque was built on the foundation of the temple and that there were several Hindu idols and structures hidden inside the mosque.

The court directed the ASI to form a five-member committee of experts to conduct a comprehensive physical survey of the entire Gyanvapi compound using non-invasive techniques such as ground-penetrating radar (GPR) and carbon dating.

The survey is expected to reveal whether there are any traces of a temple or other Hindu structures below or within the mosque and to establish the age and origin of the existing structures.

The court also appointed an observer to monitor and supervise the survey process and report any irregularities or violations.

What are Non-Invasive Methods in Archaeological Prospecting?

Non-invasive methods are used when investigations are undertaken inside a built structure and no excavation is permitted.

Types of Methods:

Active Methods: Inject energy into the ground and measure the response. The methods provide an estimate of the ground’s material properties, such as density, electrical resistance, and wave velocity.

Seismic Techniques: Use shock waves to study subsurface structures.

Electromagnetic Methods: Measure electromagnetic responses after energy injection.

Passive Methods: Measure existing physical properties.

Magnetometry: Detect magnetic anomalies caused by buried structures.

Gravity Surveying: Measure gravitational force variations due to subsurface features.

Ground-Penetrating Radar (GPR):

ASI will use GPR to produce a 3-D model of buried archaeological features.

GPR operates by introducing a short radar impulse from a surface antenna and records time and magnitude of return signals from the subsoil.

Radar beam spreads like a cone, causing reflections before the antenna passes over the object.

Radar beams spread out in a cone, leading to reflections that may not directly correspond to physical dimensions, creating false images.

Carbon Dating:

Determine organic material age by measuring carbon content.

What are the Limitations of Various Methods in Archaeological Surveys?

Similar physical properties of different materials can generate the same response, leading to ambiguity in identifying targets.

Data collected is limited and contains measurement errors, making it challenging to accurately estimate the spatial distribution of properties.

Archaeological structures are often made of heterogeneous materials with complex geometry, making data interpretation challenging.

Geophysical tools might not accurately reconstruct target images, especially in complex scenarios.

In cases like disputes over religious sites, emotional and political factors can influence interpretations and decisions.