Since the late 1970s, reasonably accurate remote sensing of the oceans from aircraft and satellites has been possible. Remote sensing depends on sensors mounted in the aircraft or satellite, picking up naturally occurring electromagnetic
radiation, or generating electromagnetic energy and measuring it after reflection from the sea.
The advantage of these new systems is that large areas can be surveyed at one time. Considerable skill goes into the design of the sensors and the interpretation of the resulting data. The data that such systems can collect are restricted mainly to surface waters and concerns the temperature, colour, roughness and average slope of the sea surface. From these four basic measurements various characteristics can be derived. Perhaps the best known is an estimate of the chlorphyll content of the water which is related to primary production. This is derived from the colour of the surface waters and allows the production of monthly maps of primary productivity throughout the world's oceans. Other applications include investigating ocean currents from the surface slope; deriving wind speed from surface roughness; using temperature patterns to help predict events such as El Niño (see Section 1.3.6) and to provide information regarding boundaries of water masses and mixing processes; and determining the source and extent of sediment and pollution plumes from colour measurements (Robinson and Guymer, 1996). The latter is particularly useful for bodies such as the UK NRA (National Rivers Authority) charged with monitoring the quality of coastal waters.
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Renewable energy is energy that is generated from sunlight, rain, tides, geothermal heat and wind. These sources are naturally and constantly replenished, which is why they are deemed as renewable. The usage of renewable energy sources is very important when considering the sustainability of the existing energy usage of the world. While there is currently an abundance of non-renewable energy sources, such as nuclear fuels, these energy sources are depleting. In addition to being a non-renewable supply, the non-renewable energy sources release emissions into the air, which has an adverse effect on the environment.