Integration of backscatter thresholds from Sentinel-1 with spectral indices and signatures from Sentinel-2 for the detection of oil spills at sea: The case of Lima, Peru

Abstract

The detection and monitoring of oil spills at sea (OSS) are essential for environmental disaster management and the protection of marine ecosystems. The objective was to integrate scattering coefficient (σ⁰) data from Sentinel-1 (S1) with multispectral images from Sentinel-2 (S2) for OSS detection, as in the case that occurred on January 15, 2022, at the La Pampilla refinery in Ventanilla, Lima, Peru. To achieve this, the σ⁰ values in VV polarization from S1-GRDH were analyzed, establishing characteristic threshold ranges of −21 dB to −13 dB for fresh oil (January 25) and −19 dB to −13 dB for weathered oil (February 2). This 3 dB shift in the median quantifies the weathering and emulsification processes of the hydrocarbon. The methodology employed includes the calculation of spectral indices (OSI, VNRI, IVI, Zakzouk) and the evaluation of S2 spectral signatures. The OSI, with a range of 1.1 to 1.5, achieved the highest agreement (κ = 0.808, “Very good”), establishing itself as the most reliable indicator for operational binary detection. Although OSI is optimal for binary detection, net area quantification was performed by spectral unmixing, yielding 6818 ha (∼68 km²). Validation using the Kappa index and Mann-Whitney-Wilcoxon U test (p < 0.05) demonstrated statistical significance and confirmed the spectral homogeneity of the signatures. The findings include this oil spill map, which establishes the Ventanilla spill as the largest ecological disaster in Peruvian history. This methodological framework is effective for the studied event and provides a reference that can be adapted to future oil spill events, contributing to the development of capabilities for rapid response to marine environmental disasters.