Page 36 - The ROV Manual - A User Guide for Remotely Operated Vehicles 2nd edition

24 CHAPTER 2 The Ocean Environment
Table 2.2 Ocean Coverage Distribution
106 km2 Percentage of Earth’s Surface Area
Continental margin Deep basins
Total
93 18.2 268 52.6 361 70.8
sediments and are the focus of exploration and production efforts. The general bottom characteris- tics of this shelf are mud and sediment.
2.2 Chemical oceanography
Water is known as the “universal solvent.” While pure water is the basis for life on earth, as more impurities are added to that fluid the physical and chemical properties change drastically. The chemical makeup of the water mixture in which the ROV operates will directly dictate operational procedures and parameters if a successful operation is to be achieved.
Two everyday examples of water’s physical properties and their effect on our lives are (i) ice floats in water and (ii) we salt our roads in wintertime to “melt” snow on the road. Clearly, it is important to understand the operating environment and its effect on ROV operations. To accom- plish this, the properties and chemical aspects of water and how they are measured will be addressed to determine their overall effect on the ROV.
The early method of obtaining environmental information was by gathering water samples for later analysis in a laboratory. Today, the basic parameters of water are measured with a common instrument named the “CTD sonde.” Some of the newest sensors can analyze a host of parameters logged on a single compact sensing unit.
Fresh water is an insulator, with the degree of electrical conductivity increasing as more salts are added to the solution. By measuring the water’s degree of electrical conductivity, a highly accu- rate measure of salinity can be derived. Temperature is measured via electronic methods, and depth is measured with a simple water pressure transducer. The CTD probe measures “conductivity/tem- perature/depth,” which are the basic parameters in the sonic velocity equation. Newer environmen- tal probes are available for measuring any number of water quality parameters such as pH, dissolved oxygen and CO2, turbidity, and other parameters.
The measurable parameters of water are needed for various reasons. A discussion of the most common measurement variables the commercial or scientific ROV pilot will encounter, the infor- mation those parameters provide, and the tools/techniques to measure them follows.
2.2.1 Salinity
2.2.1.1 Salt water
The world’s water supply consists of everything from pure water to water plus any number of dis- solved substances due to water’s soluble nature. Water quality researchers measure salinity to assess the purity of drinking water, monitor salt water intrusion into fresh water marshes and groundwater aquifers, and research how the salinity will affect the ecosystem.