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thomas712
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Originally Posted by wattsupdoc
.Also how the refraction of light through water comes into play here and why at18 inches this isnt discussed much but with a tall 65 which is 24 in it seems to be an issue..
I can't post the link or all of the articl cause it has too many adds and things that will not copy here, but this may help answer that quesion. It starts before this and ends well afterwards, quite technical.
Excerpt:
Underwater Light Field in Nature
Once the photons of light have made it all the way from the sun and across the air-water surface on the coral reefs, lets see what happens to them when they get into the water. The light traveling from the top of the water surface toward the bottom is called downwelling light. Some of the downwelling light gets absorbed, and some is scattered by the dissolved and particulate matter in the water and by the water molecules themselves. Turbidity is a term used to describe the amount of particulate matter. The higher the turbidity, the more light that is absorbed and scattered. The absorption and scattering result in reduction in the quantity of downwelling light as the depth increases (Kirk, 1994). Once the photons enters the water, most photos are eventually absorbed - either by the light absorbing molecules of the water, the optically active dissolved substances, the particulate matter, and eventually by the photosynthetic process that occurs in the corals and the suspended phytoplankton in the water column.
Further, the scatter also creates some upwelling light (backscattering of light). Some of this upwelling light escapes out of the water back into the air and is the reason for the color of the ocean. On coral reefs, the upwelling irradiance is also increased by reflection from the "white" calcium carbonate substrate found on the reef floor. In fact, on coral reefs this upwelling irradiance may be a significant portion of the total irradiance (Dustan 1982). This upwelling light plays a critical role in allowing the growth of corals on the under storey of the reefs. Thus, the addition of a white calcium carbonate substrate in a reef aquarium also helps in increasing the upwelling irradiance, while simultaneously increasing the biodiversity. Rather than covering all the sand with live rock, a good strategy would be to provide large open sand areas to increase upwelling irradiance.
Natural waters have what are often referred to as inherent and apparent optical properties. Inherent optical properties (IOP) are a function of the water and optically active substances in it and are not influenced by the geometric structure of the light fields. IOP were usually determined in the laboratory but now routinely measured in situ too and include the following (all units are m-1):
absorption coefficient (a) - fraction of the incident flux absorbed divided by
the thickness of an infinitesimally thin layer of medium
scattering coefficient (b) - fraction of the incident flux scattered divided by
the thickness of an infinitesimally thin layer of medium
beam attenuation coefficient (c) - fraction of incident flux which is absorbed
and scattered divided by the thickness of an infinitesimally thin layer. The beam
attenuation coefficient is the sum of the absorption and scattering coefficients:
c = a + b
Apparent optical properties (AOP) are derived from measurements of natural light fields in a water body. They depend on the geometry of the light fields and are related to absorption and scattering. The most common of these properties is the diffuse attenuation coefficient for downwelling irradiance (Kd). Irradiance at a given depth (EZ) is a function of the irradiance at the surface (E0), the diffuse attenuation coefficient, and the depth interval (Z) according to the following relationship, where e is the base of the natural logarithms:
.Also how the refraction of light through water comes into play here and why at18 inches this isnt discussed much but with a tall 65 which is 24 in it seems to be an issue..
I can't post the link or all of the articl cause it has too many adds and things that will not copy here, but this may help answer that quesion. It starts before this and ends well afterwards, quite technical.
Excerpt:
Underwater Light Field in Nature
Once the photons of light have made it all the way from the sun and across the air-water surface on the coral reefs, lets see what happens to them when they get into the water. The light traveling from the top of the water surface toward the bottom is called downwelling light. Some of the downwelling light gets absorbed, and some is scattered by the dissolved and particulate matter in the water and by the water molecules themselves. Turbidity is a term used to describe the amount of particulate matter. The higher the turbidity, the more light that is absorbed and scattered. The absorption and scattering result in reduction in the quantity of downwelling light as the depth increases (Kirk, 1994). Once the photons enters the water, most photos are eventually absorbed - either by the light absorbing molecules of the water, the optically active dissolved substances, the particulate matter, and eventually by the photosynthetic process that occurs in the corals and the suspended phytoplankton in the water column.
Further, the scatter also creates some upwelling light (backscattering of light). Some of this upwelling light escapes out of the water back into the air and is the reason for the color of the ocean. On coral reefs, the upwelling irradiance is also increased by reflection from the "white" calcium carbonate substrate found on the reef floor. In fact, on coral reefs this upwelling irradiance may be a significant portion of the total irradiance (Dustan 1982). This upwelling light plays a critical role in allowing the growth of corals on the under storey of the reefs. Thus, the addition of a white calcium carbonate substrate in a reef aquarium also helps in increasing the upwelling irradiance, while simultaneously increasing the biodiversity. Rather than covering all the sand with live rock, a good strategy would be to provide large open sand areas to increase upwelling irradiance.
Natural waters have what are often referred to as inherent and apparent optical properties. Inherent optical properties (IOP) are a function of the water and optically active substances in it and are not influenced by the geometric structure of the light fields. IOP were usually determined in the laboratory but now routinely measured in situ too and include the following (all units are m-1):
absorption coefficient (a) - fraction of the incident flux absorbed divided by
the thickness of an infinitesimally thin layer of medium
scattering coefficient (b) - fraction of the incident flux scattered divided by
the thickness of an infinitesimally thin layer of medium
beam attenuation coefficient (c) - fraction of incident flux which is absorbed
and scattered divided by the thickness of an infinitesimally thin layer. The beam
attenuation coefficient is the sum of the absorption and scattering coefficients:
c = a + b
Apparent optical properties (AOP) are derived from measurements of natural light fields in a water body. They depend on the geometry of the light fields and are related to absorption and scattering. The most common of these properties is the diffuse attenuation coefficient for downwelling irradiance (Kd). Irradiance at a given depth (EZ) is a function of the irradiance at the surface (E0), the diffuse attenuation coefficient, and the depth interval (Z) according to the following relationship, where e is the base of the natural logarithms:
hotsynthetic available radiation
