# Improving the RST-OIL Algorithm for Oil Spill Detection under Severe Sun Glint Conditions
## 1 Introduction
Furthermore, they are also primarily designed to provide detailed mapping of the affected areas only once oil presence is known, which results in them not being particularly useful for providing the first alert. The suitable spectral region for oil recognition ranges from the visible (VIS)-near infrared (NIR), namely the VNIR region, to the thermal infrared (TIR). In the TIR region, oil is discriminated against surrounding water due to the different brightness temperatures of the two elements directly related to their own thermal inertia characteristics and the oil type and thickness [5; 14; 25; 26; 27; 28; 29; 30]. In the VNIR, discrimination is based on the different oil and water reflectance properties. However, this difference is not unique and it is possible that the oil presence on the sea surface produces both an increase (positive contrast) and a decrease (negative contrast) in reflectance due to the different unpredictable factors related to the acquisition geometry (zenith and azimuth sun-sensors angles) as well as oil and environmental characteristics [31; 32; 33; 34]. Among the optical methods, the Robust Satellite Technique (RST) [35] specifically applied to oil spill detection, namely RST-OIL [27; 28; 36; 37; 38], has been demonstrated to detect the oil presence, using both TIR (in terms of brightness temperature) and VNIR (in terms of Rayleigh-corrected reflectance) data using automatic, self-adaptive thresholds. The methodology identifies significant statistical deviation of the measured signal on the basis of its preliminary characterization in terms of the expected value (temporal mean) and normal variability (standard deviation). To this aim, historical long-term time series of satellite data that are homogeneous in the spectral, spatial, and temporal domains are analyzed. In this work, an advanced RST-OIL configuration is proposed, especially for data acquired in the NIR band (i.e., 0.8 \(\upmu\)m) by the Moderate Resolution Spectroradiometer (MODIS) with the main goal being to face some limits appearing when the sun glint affects the investigated scene. For a differential approach like RST, the random appearance of glint/no-glint conditions may have a negative impact on the characterization of the expected signal (i.e., on the temporal mean and standard deviation computation). Thus, the proposed new RST-OIL configuration aims to extend its application to different observation conditions in order to further enlarge its range of applicability. The spill event caused by the explosion and sinking of the DeepWater Horizon Platform (DWH) in the Gulf of Mexico has been selected as a test case. The accident started on 20 April 2010 and continued up until 15 July 2010, and produced a total of about 5 million barrels of spilled oil. This event prompted scientists, the academic community, and the private sector to spend their work and time finding modern technologies to map the spilled oil and simulate its transport over the sea in order to give a rapid response and manage the effects on the environment [39]. One of the peculiarities of the area is that, at the time of Aqua and Terra satellites overpass (i.e., the two satellites carrying MODIS onboard), it can exhibit different sun-satellite geometry acquisitions up to severe sun glint conditions, which represents a suitable case study for testing the new proposed RST-OIL configuration.