Principles
In the broadest sense, remote sensing is the measurement or acquisition of information of an object or phenomenon, by a recording device that is not in physical or intimate contact with the object. In practice, remote sensing is the utilization at a distance (as from aircraft, spacecraft, satellite, or ship) of any device for gathering information about the environment. Passive optical sensors detect natural energy (radiation) that is emitted or reflected by the object or scene being observed. Reflected sunlight is the source of radiation measured by passive optical sensors.
In marine and aquatic environments, the sunlight spectrum is modified on its way through the atmosphere, the water surface, and the water body. In each of these boundary layers sunlight is absorbed, scattered, and reflected in a specific manner, depending on the wavelength. As a result, the reflected light carries spectral information about the particular composition of these matters.
Data processing
Different remote sensing data processing methods are available to retrieve thematic information from remote sensing data. With mathematical and statistical methods the spectral information is analysed. Pixels are compared to specific class signatures and assigned depending on the similarity. Physics-based retrieval algorithms model the complex light interactions with the atmosphere and the water body based on physical principles. Once set up, these optical models do not require manual adaptation in order to generate map products and are often independent of ground truth measurements. These algorithms are very flexible and may be applied worldwide and are very under all conditions covered by the optical models upon which they are based. |