| Popis: |
The focus of today's oceanographic research is shifting to shallow water environments. This region of study complicates measurement techniques by forcing the protection of the instruments from bio-fouling. The most common methods of protecting optical surfaces use compounds such as tin and copper. These paints are designed to work most effectively against large fouling organisms. Yet optical degradation also occurs with micro-fouling which is not retarded by these paint compounds. Wet Labs, Inc. recently developed an anti-fouling technique which leaches a bromide compound into a sample chamber and pumps new water into the chamber prior to measurement. This technique was first used on their chlorophyll absorption meters. Several deployments of those instruments were made for the Massachusetts Water Resources Authority (MWRA) at a long term monitoring site off of Boston, MA. The USGS has been able to compare the effectiveness of the pumped bromide technique with that of a ring impregnated with an antifoulant that surrounds the lens of a transmissometer. The results do not indicate that one technique is strongly superior over the other from the standpoint of protection. The primary advantage of using bromide is that it is less toxic than the metal based antifoulants. One other advantage to the bromide technique is the use of the flow tube sample chamber(s). It eliminates sample noise from biological life, such as fish. However, the bromide technique has two drawbacks. First, to allow a sufficient amount of bromide to settle into the sample chamber to be effective, the manufacturer suggests that the maximum sampling frequency be not more than once per hour. This restriction may interfere with the scientific objectives. Second, mesh screening protects the input to the sample chambers. Without some passive anti-fouling protection of those screens, these screens will become clogged with biofouling. |
