Multifrequency radar imagery and characterization of hazardous and noxious substances at sea

Abstract

The increase in maritime traffic, particularly the transport of hazardous and noxious substances (HNSs), requires advanced methods of identification and characterization in environmental chemical spills. Knowledge about HNS monitoring using radar remote sensing is not as extensive as for oil spills; however, any progress on this issue would likely advance the monitoring of both chemical and oil-related incidents. To address the need for HNS monitoring, an experiment was conducted in May 2015 over the Mediterranean Sea during which controlled releases of HNS were imaged by a multifrequency radar system. The aim of this experiment was to establish a procedure for collecting evidence of illegal maritime pollution by noxious liquid substances using airborne radar sensors. In this paper, we demonstrate the ability of radar imagery to detect and characterize chemicals at sea. A normalized polarization difference parameter is introduced to quantify both the impacts of released product on the ocean surface and the relative concentration of the substance within the spill. We show that radar imagery can provide knowledge of the involved HNS. In particular, one can distinguish a product that forms a film on the top of the sea surface from another that mixes with seawater, the information that is critical for efficient cleanup operations.

SAR Imagery for Detecting Sea Surface Slicks: Performance Assessment of Polarization-Dependent Parameters

“…In the second case (film), radar backscattered power is mainly diminished through mechanical damping of Bragg-wavelength gravity-capillary waves. The capability of radar imagery to distinguish between substances that manifest as a thin film on the sea surface or that mixes with seawater near the surface has already been demonstrated in the case of mineral oil [26] and chemicals [27]. If the thickness of the film on the top of the sea surface is small compare to the penetration depth, δ p , the EM wave will penetrate the film to scatter from the water below the film, so the effective dielectric constant will be that of seawater, and not that of the product which forms the film.…”

“…Because of their physico-chemical properties, these two substances have different behaviors once released into the ocean. FAME forms a cloud in the water column composed by micro-droplets while rapeseed oil remains above the surface and produce a film [27]. These two behaviors have been highlighted in [27], using the oilwater mixing index introduced in [26].…”

“…FAME forms a cloud in the water column composed by micro-droplets while rapeseed oil remains above the surface and produce a film [27]. These two behaviors have been highlighted in [27], using the oilwater mixing index introduced in [26]. oil by the green box, the blue box corresponds to a mixture between the two products.…”

Marine Oil Slicks Quantification From L-band Dual-Polarization SAR Imagery

“…The most relevant radar parameters for marine oil slicks detection have been recently identified in [25] together with the most appropriate imaging mode in the context of marine pollution detection. Different studies have concentrated their efforts to characterize and discriminate oil spills from look-alike phenomena [26], [27] while others have investigated the mixing of oil and seawater from SAR sensors [28]- [30]. Up to now, only an oil/seawater mixing classification have been proposed, namely, the oil/seawater mixing index M (−1 ≤ M ≤ 1) [28].…”

“…Positive values indicate an attenuation mostly due to surface roughness damping from a surface film whereas negative values indicate an attenuation mostly due to a modification of the relative complex permittivity from a mixture of oil and seawater. This index has been used later in [30] where a methodology has been proposed based on dual co-polarized (HH and VV ) SAR images to detect and quantify the relative concentration of pollutant on the ocean surface.…”