Page 55 - The ROV Manual - A User Guide for Remotely Operated Vehicles 2nd edition

2.2.15 Ionic concentration
There are four environmentally important ions: nitrate ðNO23 Þ, chloride (Cl2), calcium (Ca21), and ammonium ðNH14 Þ. Ion-selective electrodes used for monitoring these parameters are described below.
• Nitrate ðNO23 Þ: Nitrate ion concentration is an important parameter in nearly all water quality studies. Nitrates can be introduced by acidic rainfall, fertilizer runoff from fields, and plant or animal decay or waste.
• Chloride (Cl2): This ion gives a quick measurement of the salinity of water samples. It can even measure chloride levels in ocean salt water or salt in food samples.
• Calcium (Ca21): This electrode gives a good indication of the hardness of water (as Ca21). It is also used as an end point indicator in EDTA-Ca/Mg hard water titrations.
• Ammonium ðNH14 Þ: This electrode measures levels of ammonium ions introduced from fertilizers. It can also indicate aqueous ammonia levels if sample solutions are acidified to convert NH3 to ðNH14 Þ.
2.2.16 Solar radiation
Solar radiation is the electromagnetic radiation emitted by the sun and is measured in some under-
water scientific applications.
2.2.17 Light and other electromagnetic transmissions through water
Light and other electromagnetic transmissions through water are affected by the following three
factors:
1. Absorption 2. Refraction 3. Scattering
All of these factors, which can be measured by the ROV using light sensors, are normally lumped under the general category of attenuation.
2.2.17.1 Absorption
Electromagnetic energy transmission capability through water varies with wavelength. The best penetration is gained in the visible light spectrum (Figure 2.13). Other wavelengths of electromag- netic energy (radar, very low-frequency RF, etc.) are able to marginally penetrate the water column (in practically all cases only a few wavelengths), but even with very high intensity transmissions only very limited transmission rates/depths are possible under current technologies. Submerged sub- marines are able to get RF communications in deepwater with very low-frequency RF, but at that frequency it may take literally minutes to get through only two alphanumeric characters.
In the ultraviolet range, as well as in the infrared wavelengths, electromagnetic energy is highly attenuated by seawater. Within the visible wavelengths, the blue/green spectrum has the greatest energy transparency, with other wavelengths having differing levels of energy transmission.
2.2 Chemical oceanography 43