UNDERWATER RADIATION MEASUREMENTS: CONSEQUENCES OF AN INCREASED UV-B RADIATION

摘要

Almost all outdoor living organisms are exposed to ultraviolet radiation (UV). Ecosystems experience from morning to evening a strong variation of UV intensity due to diurnal changes in solar elevation, which depends on latitude and time of the year. These changes are the most dominant factor causing short term variation in UV radiation on Earth. The amount of UV radiation reaching the surface at any time also depends on atmospheric factors. Components such as ozone and particulate matter in the form of clouds and aerosols absorb solar radiation and cause both short term and long term variability. In the UV range scattering processes are also important and reflection from the ground influences radiation levels measured at the surface. All changes in UV caused by atmospheric factors, such as, for instance, ozone depletion, increased amount of aerosols or increased cloud cover, influence of course the amount of UV in water. To assess the amount of radiation into the water one has to consider radiative transfer in the water and particular components which strongly absorb ultraviolet radiation, such as humic substance, also called gelbstoff or CDOM (Chromophoric Dissolved Organic Matter). Moreover at the air-water boundary the index of refraction changes and must be taken into account when penetration of UV into water is investigated.