Open-Earth-Monitor Global Workshop 2026

The coastal border of Semarang and Demak in Central Java, Indonesia, faces unprecedented mangrove deforestation driven by rapid land subsidence, sea-level rise, aquaculture expansion, and industrialization. Traditional optical remote sensing approaches are severely constrained by persistent cloud cover in this tropical environment, resulting in detection lags of weeks to months that preclude timely intervention. This study presents an iterative Bayesian updating framework for near-real-time mangrove deforestation monitoring through multi-sensor fusion of Sentinel-1 Synthetic Aperture Radar (SAR) and optical imagery from Landsat-8/9 and Sentinel-2. We formulate a probabilistic change detection model where posterior deforestation probabilities are sequentially updated with each new satellite observation, incorporating VH-polarized backscatter from Sentinel-1 alongside three complementary optical indices: Normalized Difference Vegetation Index (NDVI), Mangrove Vegetation Index (MVI), and Enhanced Mangrove Index (EMI). Four experimental scenarios were evaluated across the 2018-2025 period: (1) SAR-Optical Baseline (VH + NDVI), (2) Structure-Focused (VH + MVI), (3) Moisture/Soil-Focused (VH + EMI), and (4) Full Integrated Suite (VH + EMI + NDVI + MVI). Validation through field surveys, high-resolution imagery, and comparison with existing deforestation maps demonstrated that Scenario 4 achieved the highest F1-score (0.89) and lowest detection lag (8.3 days median), reducing false positives from tidal flooding by 67% compared to single-sensor approaches. The integration of structural information from SAR and MVI with spectral-moisture signals from EMI and NDVI enabled robust discrimination between genuine deforestation events and natural tidal dynamics. Mathematical formulations for prior specification, likelihood functions, and posterior updating are presented in detail, alongside practical implementation considerations for tropical coastal environments. These findings provide actionable guidance for local coastal management agencies in Semarang-Demak to implement operational near-real-time monitoring systems that can trigger rapid response to illegal logging and land conversion.