Minimize Oil Pollution

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Introduction

Mineral oil spilled by ships or offshore oil platforms or due to natural oil seepage from subsea deposits becomes visible on SAR images because it damps short surface waves and thus reduces the backscattered radar power over these areas. Such slicks therefore show up as dark areas on SAR images. However, dark patches on SAR images of the ocean surface do not always originate from mineral oil films. They can originate, e.g., (1) from natural surface films which are produced by plankton or fish and which also strongly damp the surface waves, (2) from low winds which are often encountered in the lee of islands or coastal mountains, and (3) from cold water, as encountered, e.g., in upwelling areas which changes the stability of the air-sea interface and thus the ability of the wind to generate small-scale ocean waves.

But often mineral oil spills released from ships can be identified by their location and by their shape. When released from traveling ships, they form elongated trails.

Figure 1

Figure 1: Ocean currents and winds sometimes deform the shape of the oil trail. The wind often gives rise to a "feathered" structure of the trail. The "feathered" side is always located upwind as depicted in the figure.

Figure 2

Figure 2: Section of an ERS-2 SAR image from the Indian Ocean (6 April 1999, 4:58 UTC, orbit: 20700, frame: 3393, frame center: 10° 36'N, 81° 49'E) showing a "feathered" structure of an oil trail. By the action of the wind the heavy components of the mineral oil film accumulate at the downwind side (dark line in the image). The "feathered" side is always located upwind.

References

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