How much oil is in this area? The inability to accurately measure the volume of oil deposited into the ocean from natural causes or improperly maintained oil platforms has caused the reported amounts of pollution to be inaccurate. The density and hydrophobic properties of oil causes the pollution to float upon the surface of the water, because of this, visual methods have long been the norm for monitoring oil slicks. The estimation of areas covered by oil of such a magnitude leaves a large margin of error. By utilizing satellite images, a more quantitative visual method can be utilized in determining the volume of oil covering an area of water.
Analysis of a SAR image can supply an area of water in which oil rests on the surface (called a slick), causing dark areas in the image where the radio signal does not return strongly to the satellite.
Based on past experience, SkyTruth has determined that a good rule of thumb for estimating the thickness of an oil slick visible in a SAR image is that the total area is about 1µm (one micron) thick. The actual thickness varies across the whole area, as some areas may be thicker than assumed, or undetectable due to being too thin or patchy to consider measurable.
By measuring the area of the visible oil slick in a SAR image, and assuming the average thickness of the oil across the entire area is 1µm the volume of oil in the slick can be calculated.
If there was a slick of oil covering one km2, then
the volume of the oil covering this surface can be calculated:
Conveniently, one square kilometer of oil covering the water,
multiplied by a µm thickness is equal to 1m3
(a measurement of volume).
According to Google, 1 meter3 is equal to 264.17
US gallons, so 264.17 US Gallons of oil at an average thickness of 1µm can cover 1km2 of
Using Dimensional analysis, we determined how much 1 µm thick
oil covers different areas:
With this information, multiplying the amount of area
effected by the oil by the appropriate unit, will supply the total volume of a
slick, in gallons. A 1m2
slick of oil contains 2.64x10-4
If an analyzed image shows a slick that covers 50 mi2:
(683.76 Gallons of Oil/mi2) (50mi2) = 34,188 Gallons of Oil.