Archaeological investigation by ground penetrating radar at Wiang Kaew site in Chiang Mai city moat, Thailand

Abstract

This study employed ground-penetrating radar (GPR) to investigate the existence of the walls of Wiang Kaew Palace within the urban setting of Chiang Mai City Moat, Thailand. The 1893 old Chiang Mai City map precisely delineates the presence and locations of the ancient palace. In 2018, archaeologists unearthed parts of the buried remnants of Wiang Kaew Palace walls inside the Former Woman Correctional Institute. However, other sections of the Wiang Kaew wall in the surrounding area remain undiscovered. According to the fact that GPR is a non-destructive geophysical method, the PulseEKKO® system, using frequencies of 250- and 500-MHz antenna, was employed to further investigate the hidden remnants of the Wiang Kaew Palace walls. Easily accessible areas were chosen and included in the investigation. The GPR surveys were performed using a grid system. The radar data were affected by noise from rebar, a moist soil zone, and a drainage system. The GPR data underwent standard data processing stages and the wall structure was interpreted based on various characteristics including depth, width, continuity, diffraction, and planar reflection. The attribute analysis tool, envelope, was utilized to improve the migrated data to figure out the depths, widths, and thickness of the buried targets. Amplitude depth slices and isosurfaces were created using the envelope data to interpret and visualize the wall structure, in addition to the GPR sections. The GPR data reveals the presence of sections of the walls of Wiang Kaew Palace in three parts: the south wall, the front wall, and the north wall. Other attributes such as instantaneous phase, instantaneous frequency, instantaneous bandwidth, and similarity are partially associated with section interpretation in this work. Results from GPR depth slices, isosurfaces, unmigrated sections, envelope sections, and attribute analysis support the possibility of having archaeological structures of Wiang Kaew Palace. Twenty anomalies may be involved with the palace walls: four anomalies for the south wall, ten anomalies for the front wall, and six anomalies for the north wall. The depiction of possible locations of the walls of Wiang Kaew Palace from this study provide valuable information in the fields of Chiang Mai urban planning, as well as archaeological preservation and excavation.