**5. Potential of radar and microwave techniques for detecting oil spills**

Oil on the sea surface dampens some of the small capillary waves that occur naturally in clean seas. Capillary waves reflect radar energy, producing a "bright" area in radar imagery. The presence of an oil slick can be detected as a "dark" area or one that has an absence of sea clutter. In this regard, Synthetic Aperture Radars (SARs) and Side-Looking Airborne Radars (SLARs) are the two primary types of radars used for environmental remote sensing and oil spill response. SLARs, despite being an older technology, are less expensive to purchase and use long antennas to improve alongtrack resolution. SARs achieve along-track resolution by using the forward motion of the sensor (an aircraft or spacecraft) to generate a very long antenna (which is range independent). A SAR signal requires sophisticated electronic processing to extract images. SARs are more expensive than SLARs but have a wider field of view and higher resolution. Comparative tests reveal that SAR is significantly better. Because

they are made to identify complex targets, search, and rescue radar systems have little to no use for locating oil spills [16–22].

Radar detection of oil slicks is limited by sea state, low sea states will not produce sufficient clutter in the surrounding sea to contrast with the oil, and very high seas will scatter radar sufficiently to block detection inside the troughs. Indications are that wind speeds of at least 1.5 m/s are required as a minimum to allow detectability. Beyond this, wind speeds higher than 6 m/s will again remove the effect of an oil slick being distinguishable from the surrounding sea [9, 22–24].

Microwave radiation is emitted by the ocean. Because oil emits more microwave radiation than water, it appears as a "bright" area on a darker sea because oil is a stronger microwave emitter than water. Oil has a higher emissivity than water, which has a 0.4 emissivity factor. This difference in emissivity can be picked up by a passive device, which could act as a method of oil detection. The device could theoretically be used to measure the thickness of a slick because there is also a change in signal with thickness. This method has been very effective [20, 22, 24].

The methodology is dependent on prior knowledge of a range of environmental and oil-specific parameters, and the signal return is periodically influenced by oil thickness. Any one of two or three film thicknesses can be inferred from a given signal strength for a specified slick. When the effective thickness is an odd multiple of a quarter wavelength of the observed energy, microwave emission is at its highest. Additionally, the signal-to-noise ratio is low and biogenic materials interfere. Achieving high spatial resolution is challenging [1, 22, 24].
