ISO 7027-2:2019 pdf free

ISO 7027-2:2019 pdf free.Water quality一Determination of turbidity
The depth at which a matt white, circular disc (5.2.1.1) is no longer visible is taken as a measure of the transparency of surface water bodies. The readings do not provide an exact measure of transparency,as the results are influenced e.g. by sun’s glare on the water, water current and/or individually different eyesight of the staff.
NOTE 1 This method was originally developed by A. Secchi (1865)[4], and modified by George C. Whipple (1899) [5], and is commonly known as Secchi depth.
NOTE 2 For assessments in connection with phytoplankton investigations, the transparency depths are normally used.
NOTE 3 In very tide-influenced coastal waters or in reservoirs with turbidity currents (e.g. from tributaries),the results in relation to phytoplankton are not very informative because the results are influenced by very high concentrations of suspended mineral matter. Humic substances can considerably reduce the transparency.
The transparency depth can be recorded most easily and reliably by looking from a small distance above the water surface into the water. It is highly recommended to use the shaded side of the boat,dock or footbridge to avoid direct sunlight reflections from the water surface. It is essential that no direct sunlight is present. The period for best results is between 10 am and 2 pm. Allow sufficient time when looking at the disc near its extinction point for the eyes to adapt completely to the prevailing luminance level.
Lower the disc (5.2.1.1) into the water and let it sink slowly. Determine the point at which the surface of the disc is just visible. If necessary, slowly move the disc several times up and down, to determine the mean of disappearance and reappearance. Ensure that the visual line is perpendicular to the water surface.
To minimize interferences arising from reflection at the water surface, a sight glass (for example view scope, see A.2) may help. With a view scope, the sunny side of the boat can be used (see Reference [3]).The user of this document shall validate and demonstrate whether the view scope enhances the analysis or not.ISO 7027-2 pdf free download.