Detecting and Monitoring Small-Scale Mining Footprints in Opol, Misamis Oriental, Using Sentinel-1 SAR Backscatter and Time-Series Feature Analysis

Artisanal and small-scale gold mining (ASGM) is responsible for the destruction of tropical watersheds and monitoring its dispersed footprint can be constrained by uneven terrain and constant cloud cover. In response to these significant difficulties, this study sets forth an automated cloud-resilient framework utilizing multi-temporal Sentinel-1 C-band and cross-polarized SAR (Synthetic Aperture Radar) with QGIS hydrologic topology to monitor illegal mining and riparian encroachment within the Iponan River watershed (Opol, Northern Mindanao) from 2021–2025. To address rapid regrowth of tropical vegetation and capture peak structural disturbances, annual minimum backscatter layers were extracted and binarized using optimized empirical thresholds (<0.01 for 2021–2024; <0.015 for 2025) to isolate the specular water-saturated excavation pit signatures. The Shreve Stream Order system was applied to delineate the stream networks, which were buffered with a 100 m fixed distance vector proximity to isolate overlapping mining geometries. The spatial analyses revealed that the total peak area disturbances were identical for 2022 and 2024; both were approximately 0.6001 ha, which represents an initial horizontal expansion of 87.50% from the baseline of 0.3200 ha. Intersected spatial analyses statistically confirm tight spatiotemporal coupling of mechanized land clearing with drainage degradation. In 2022, mining operations compromised 2,879.72 m of active stream lines from 26 different segments at the peak of the expansive mining expansion. Conversely, while there was an apparent stabilization of absolute surface area in 2024, the stream network had a record number of 31 compromised drainage fractures, indicating a shift towards a highly dispersed, decentralized extraction footprint that increases the potential for downstream channel destabilization. After 2025, there were no longer any recorded active specular anomalies to validate the abrupt cessation of operations or the rapid recovery of pioneer canopy cover. This research provides evidence that comprehensive automated linear radar workflows will produce objective, cloud-free monitoring metrics essential for computational watershed management and compliance monitoring/enforcement.