Subsurface Void Detection Using Ground-Penetrating Radar in Kano City Ancient Wall Foundation Area, North West Nigeria

The ancient walls of Kano City, a UNESCO-recognised heritage structure and tourist landmark in Kano State, are underlain by centuries of historical human activity that has produced a complex subsurface of buried features, tunnels, voids, and unstable fill materials threatening the structural integrity of the walls. This study applies ground-penetrating radar to detect and map subsurface voids and anomalies beneath a 600-metre section of the ancient wall foundation. A 200 MHz antenna system was traversed along profiles parallel and perpendicular to the wall base at 2-metre intervals. Radargrams were processed using GSSI RADAN software with standard post-processing routines including background removal, bandpass filtering, and hyperbolic diffraction fitting for depth calibration. Identified anomalies were catalogued by type, depth, and plan position. Thirteen distinct void signatures were identified, with depths ranging from 0.6 to 3.2 metres below the wall base, concentrated in the western section where historical accounts describe former market tunnels. Two large anomalies exceeding 2 metres in lateral extent are flagged as immediate structural concerns. The study provides a GPR-based condition assessment map that will inform targeted conservation interventions by the Kano State History and Culture Bureau. Keywords: ground-penetrating radar, void detection, Kano ancient wall, heritage conservation, subsurface mapping