Precision Mapping of Coastal Erosion in Karaikal Using Combined UAV Photogrammetry and RTK GNSS Surveys

Coastal erosion poses a significant risk to India’s 11,098.81 km shoreline, particularly in regions where coastal economies rely heavily on fishing. Karaikal, Puducherry, has experienced erosion along 37% of its coastline (NCCR, 2018), underscoring the need for robust sediment volume and shoreline change assessments. This study quantifies sediment dynamics by integrating Unmanned Aerial Vehicle (UAV) photogrammetry with Real-Time Kinematic Global Navigation Satellite System (RTK GNSS) surveys across TR Pattinam and Vanjiur beaches. Shoreline positions were mapped using RTK GNSS by delineating the centre line between high-water (HWL) and low-water (LWL) marks, while UAV-derived edges were extracted via the Canny detection algorithm. UAV flights were conducted at 50 m altitude with 85% image overlap. The Canny method achieved an average SSIM of ~0.8 and positional accuracy within one pixel.Sediment volumes were estimated by generating UAV-based digital elevation models (DEMs) using Structure from Motion and comparing them with centimetre-accurate GNSS transects spaced at 30 m intervals. Elevation differences were integrated alongshore to compute volumetric changes, with UAV elevations cross-checked against GNSS profiles for bias assessment. Results indicate strong agreement between UAV and GNSS datasets, demonstrating the reliability of this integrate.Key words: Shoreline change, Erosion, GNSS, Edge detection ,Sediment volume