Illicit sand quarry in riverbeds will become a menace to the worldwide environment and will lead to changes in the river morphology, physical habitation and ecosystem. The excavation of sand in the riverbed is essential because it helps to maintain the river path and avoid flood inundation during the rainy season. But the excess sand removal only creates a negative impact to the surrounding environment. Hence, effective monitoring and scientific audit method are required to identify the illicit sand quarry. The assessment of excess sand excavated area and volume is a major task for the Economic and Revenue Sector Audit (E&RSA) officials. Also, the volume calculation of sand quarry is a tedious and time-consuming process when using a traditional survey instrument like total station. Integration of unmanned aerial vehicle (UAV) remote sensing (R/S) technology with modern survey instrument like differential global positioning system (DGPS) will reduce the survey time, cost and manpower. In this study, the UAV-based aerial survey and DGPS observation were done in Economic and Revenue Sector Audit (E&RSA), a specified sand quarry site. The acquired UAV aerial images and DGPS points were subsequently used to generate orthomosaic map, digital terrain model (DTM), digital surface model (DSM) and 3D mesh. The UAV-derived outputs have been compared with lease map and revenue records. All the findings related to violations in approved lease boundary, volume and depth were reported to E&RSA to estimate the revenue loss to the government.
