Thermal testing, 3D imagery to assess Charminar damage

The need to conduct the tests arose after ASI discovered that the air gap between the external lime plaster and the monument’s actual facade has been increasing

Published: 13th June 2019 08:09 AM  |   Last Updated: 13th June 2019 08:09 AM   |  A+A-

Express News Service

HYDERABAD: Nearly a month after a chunk of lime mortar fell off of Charminar’s south east minaret,  the Archaeological Survey of India is set to take the help of an unmanned aerial system (UAS) company to conduct various tests on the 16th-century monument. The need to conduct these tests came after ASI discovered that the air gap between the lime plaster and Charminar’s actual facade has been increasing. 

To measure those air gaps, Terra Drone India, on Thursday will be carrying out ultrasonic pulse velocity testing, being described as a ‘non-destructive testing technique’. In this test, the velocity of an ultrasonic pulse passing through a structure helps assess the strength and quality of the structure. Studies have claimed that this method can check both intrinsic characteristics of a material like porosity, grain size and so on, and external factors such as humidity, stress, temperature, among others. 

Terra Drone India would also prepare a ‘True Color 3D Model’ using what is being termed a ‘Visual RGB Sensor’, in which a visual (RGB) scan will be carried out to maintain a record of the facade, actual colour and any visible cracks or crevasses. A 3D model of the affected area will also be created. 

Meanwhile, a thermal scan will be done to identify the differences in temperature across different parts of the monument to understand if they are at a risk of damage, said Marcia Chen, Assistant Manager-Business of Terra Drone India. “The difference in temperature will indicate the difference in materials used since each material has its own response to heat, monsoon, etc. We’ll try to correlate that with the damage that has happened to the minaret,” Chen told Express. 

Lastly, the UAS company will also conduct a ‘LiDAR 3D Profiling and Model Generation’ test, using LiDAR 3D, a surveying method that uses light in the form of a pulsed laser to measure ranges. The LiDAR survey will help preserve the existing design and layout of the monument for future rebuilding or repair works.

The tests will first be conducted on the south east minaret. Depending on the results, the ASI will decide if the rest of the monument needs testing.

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