من طرف Hanan 1/4/2009, 14:53Remote Sensing and Surveillance of Oil Spills
Remote sensing is useful in several modes of oil spill control, including large area surveillance, site specific monitoring and tactical assistance in emergencies. It is able to provide essential information to enhance strategic and tactical decision-making .
Remote sensing devices used include the use of infra-red (IR) video and photography from airborne platforms, thermal infrared imaging, airborne laser fluouro sensors, airborne and satellite optical sensors, as well as airborne and satellite Synthetic Aperture Radar (SAR). SAR sensors have an advantage over optical sensors in that they can provide data under poor weather conditions and during darkness .
oil spills verification has based on two main parts:
1.Detection of dark spot - Locate all dark spots that can possible be oil slicks in the image and extracted the features. The dark spot are then classified into possible oil slicks and "look-alike" based on the extracted features. Verification of dark spots is based on adaptive threshold. This threshold is based on an estimate of the typical grey level (DN value). The adaptive threshold is set and moved across the image in small steps to threshold all pixels in the scene.
2.Feature extraction - For each dark spot, a set of features is computed. The features constitute of general, standard descriptions often applied for regions, and additional features particularly suited for oil slick detection. Examples of features are the contrast of the dark spot area to the surrounding sea, and the shape of the spot. These features are then calculated for each of the dark spots in order to determine the total area of oil spills by detector.
Oil Spill Remote Sensing
A common passive sensor is an infrared camera or an IR/UV (infrared/ultraviolet) system. The inherent weaknesses include the inability to discriminate oil on beaches, among weeds or debris.
Among active sensors, the laser fluorosensor is a most-useful instrument because of its unique capability to identify oil on backgrounds that include water, soil, ice and snow. It is the only sensor that can positively discriminate oil on most backgrounds.
Optical Sensors – Visible
In the visible region of the electromagnetic spectrum (approximately 400 to 700 nm), oil has a higher surface reflectance than water, but also shows limited
Oil spill surveillance
Oil spill surveillance constitutes an important component of oil spill disaster management. Advances in remote sensing technologies can help to identify parties potentially responsible for pollution and to identify minor spills before they cause widespread damage.
Ultraviolet
Ultraviolet sensors can be used to map sheens of oil as oil slicks display high reflectivity of ultraviolet (UV) radiation even at thin layers (<0.01 μm).
combining IR and UV can provide a more positive indication of oil than using either technique alone.
Infrared
Oil, which is optically thick, absorbs solar radiation and re-emits a portion of this radiation as thermal energy, primarily in the 8 to 14 μm region. In infrared (IR) images, thick oil appears hot, intermediate thicknesses of oil appear cool, and thin oil or sheens are not detected
Satellite Remote Sensing
Recently, it has been strongly suggested that satellite remote sensing could replace airborne remote sensing. However, current technologies do not support this claim. The use of satellite remote sensing for oil spills has been attempted several times
Remote sensing is useful in several modes of oil spill control, including large area surveillance, site specific monitoring and tactical assistance in emergencies. It is able to provide essential information to enhance strategic and tactical decision-making .
Remote sensing devices used include the use of infra-red (IR) video and photography from airborne platforms, thermal infrared imaging, airborne laser fluouro sensors, airborne and satellite optical sensors, as well as airborne and satellite Synthetic Aperture Radar (SAR). SAR sensors have an advantage over optical sensors in that they can provide data under poor weather conditions and during darkness .
oil spills verification has based on two main parts:
1.Detection of dark spot - Locate all dark spots that can possible be oil slicks in the image and extracted the features. The dark spot are then classified into possible oil slicks and "look-alike" based on the extracted features. Verification of dark spots is based on adaptive threshold. This threshold is based on an estimate of the typical grey level (DN value). The adaptive threshold is set and moved across the image in small steps to threshold all pixels in the scene.
2.Feature extraction - For each dark spot, a set of features is computed. The features constitute of general, standard descriptions often applied for regions, and additional features particularly suited for oil slick detection. Examples of features are the contrast of the dark spot area to the surrounding sea, and the shape of the spot. These features are then calculated for each of the dark spots in order to determine the total area of oil spills by detector.
Oil Spill Remote Sensing
A common passive sensor is an infrared camera or an IR/UV (infrared/ultraviolet) system. The inherent weaknesses include the inability to discriminate oil on beaches, among weeds or debris.
Among active sensors, the laser fluorosensor is a most-useful instrument because of its unique capability to identify oil on backgrounds that include water, soil, ice and snow. It is the only sensor that can positively discriminate oil on most backgrounds.
Optical Sensors – Visible
In the visible region of the electromagnetic spectrum (approximately 400 to 700 nm), oil has a higher surface reflectance than water, but also shows limited
Oil spill surveillance
Oil spill surveillance constitutes an important component of oil spill disaster management. Advances in remote sensing technologies can help to identify parties potentially responsible for pollution and to identify minor spills before they cause widespread damage.
Ultraviolet
Ultraviolet sensors can be used to map sheens of oil as oil slicks display high reflectivity of ultraviolet (UV) radiation even at thin layers (<0.01 μm).
combining IR and UV can provide a more positive indication of oil than using either technique alone.
Infrared
Oil, which is optically thick, absorbs solar radiation and re-emits a portion of this radiation as thermal energy, primarily in the 8 to 14 μm region. In infrared (IR) images, thick oil appears hot, intermediate thicknesses of oil appear cool, and thin oil or sheens are not detected
Satellite Remote Sensing
Recently, it has been strongly suggested that satellite remote sensing could replace airborne remote sensing. However, current technologies do not support this claim. The use of satellite remote sensing for oil spills has been attempted several times
