Decoding the stone Buddha: Three-dimensional ground penetrating radar attribute insights into cracks and restoration history of Sumeru throne

The Northern Wei dynasty stone Buddha was built in 517 AD and is currently housed in Qingdao Museum, located in Laoshan District, Qingdao, China (36°6′5.58″N, 120°28′23.42″E). Over the centuries, the natural weathering process and the damage caused by various relocations has led to internal cracks on its Sumeru throne that threatens the stability of the Buddha. Previous restoration attempts are visible on the surface of the throne. To guarantee the quality and effectiveness of further restoration measures, it is essential to thoroughly investigate the cracks developments and all invisible past restoration efforts that might interfere future restoration. An ultra-wideband stepped-frequency continuous wave (SFCW) ground penetrating radar (GPR) system was employed to perform a non-invasive investigation of the Buddha Sumeru throne. We used a systematic imaging method to tackle the challenges of detecting tiny internal features within the throne. Leveraging scattering-based velocity estimation, advanced GPR signal enhancement, Stolt migration, and envelope attribute extraction, this approach unveils a high-resolution three-dimensional (3D) image, offering unprecedented insights into subsurface structures. The obtained images revealed the internal cracks, details of past restoration effort, offering valuable insights for guiding future restoration efforts. Finally, we discussed the advantages of GPR for investigating stone statues.