Jerlov water types
The Jerlov water types are used for the optical classification of water in open oceans and in coastal waters. The water types according to Nils Gunnar Jerlov (Denmark) are a phenomenological water type classification.
Jerlov was the first to propose a classification of water masses by optical properties. Jerlov's empirical classification of the water types refers to the top 10 m of the water column of the ocean. He suggested a wavelength of 475 nm for the water analysis. In 1976, Jerlov divided seawater into water types I to III, and coastal water into water types 1 to 9, based on the spectral transmission properties of the water.
A distinction is made between the Jerlov water types:
- oceanic waters: water types I, IA, IB, II and III
- I - extremely clear sea water;
- II - tropical / subtropical sea water,
- III - sea water from the middle latitudes,
- Coastal water with different degrees of turbidity: water types 1 to 9
In his work, Jerlov found a certain attenuation coefficient for each type of water. The attenuation (German: attenuation) is the measure of the clarity of the water. The attenuation reflects the attenuation of light when passing through the body of water.
The measurement of optical components in the water column has been part of oceanography since the beginning of the 20th century . In the beginning, the measurement was optically and physically motivated, but later it became part of bio-optics in the context of biological oceanography . Bio-optics investigates the interaction of optical parameters with biological processes and the optical properties, such as scattering , absorption , fluorescence , of molecules and particles. These optical-physical examinations (marine physics) allow the determination of substances and their concentration in sea water and thus support the acquisition of information about the ocean ecosystem . The water is examined with fluorometers, turbidity sensors and various measuring methods of spectral radiometry , among other things .
The phytoplankton and resuspended sediments and particles in the water are decisive for the optical properties of the water. The fluorescence and the absorption of light by the water are decisively influenced by the absorption properties of the yellow substances present in the water . The source of the yellow substance is the breakdown of organic matter in the water. The vertical attenuation coefficient fluctuates depending on the algal biomass, which in turn is related to the photosynthetically available radiation.
The questions about the water types, the algae biomass and the photosynthetically available radiation find their applications for marine ecosystem models.
literature
- NG Jerlov: Optical Studies of Ocean Waters . In: Reports of the Swedish Deep-Sea Expedition , 3: 1-59; 1951.
- NG Jerlov: Optical Oceanography , ISBN 978-0-444-40320-9 , Elsevier, 1968. (on google-books )
- NG Jerlov, E. Steemann Nielsen: Optical aspects of oceanography . ISBN 978-0-12-384950-2 , Academic Press, London, New York, 1974.
- NG Jerlov: Marine optics . ISBN 978-0-444-41490-8 , Elsevier, Amsterdam, 1976.
- NG Jerlov: Marine Optics . In: Journal of Organometallic Chemistry Library , 1976.