Page 50 - The ROV Manual - A User Guide for Remotely Operated Vehicles 2nd edition

38 CHAPTER 2 The Ocean Environment
2.2.9 Viscosity
Viscosity is a liquid’s measure of internal resistance to flow or resistance of objects to movement within the fluid. Viscosity varies with changes in temperature/salinity, as does density. Seawater is more viscous than fresh water, which will slightly affect the computations of vehicle drag.
2.2.10 Water flow
Water flow is the rate at which a volume of water moves or flows across a certain cross-sectional area during a specified time and is typically measured in cubic feet per second/cubic meters per second (cfs/cms). The flow rate changes based upon the amount of water and the size of the river or stream being monitored. Environmental researchers monitor water flow in order to estimate pol- lutant spread, to monitor groundwater flow, to measure river discharge, to manage water resources, and to evaluate the effects of flooding.
2.2.11 Turbidity
Turbidity (which causes light scattering—see Section 2.2.17.3), the measure of the content of sus- pended solids in water, is also referred to as the “cloudiness” of the water. Turbidity is measured by shining a beam of light into the solution. The light scattered off the particles suspended in the solution is then measured, and the turbidity reading is given in nephelometric turbidity units. Water quality researchers take turbidity readings to monitor dredging and construction projects, examine microscopic aquatic plant life, and monitor surface, storm, and wastewater.
2.2.12 Chlorophyll
In various forms, chlorophyll is bound within the living cells of algae and other phytoplankton found in surface water. Chlorophyll is a key biochemical component in the molecular apparatus that is responsible for photosynthesis, the critical process in which the energy from sunlight is used to produce life-sustaining oxygen. In the photosynthetic reaction, carbon dioxide is reduced by water, and chlorophyll assists this transfer.
2.2.13 Water quality
Water quality researchers count on sensors and computer software to sense environmental waters and
log and analyze data. Factors to be considered in water quality measurement are discussed below.
2.2.13.1 Alkalinity and pH
The acidity or alkalinity of water is expressed as pH (potential of hydrogen). This is a measure of the concentration of hydrogen (H1) ions. Water’s pH is expressed as the logarithm of the reciprocal of the hydrogen ion concentration, which increases as the hydrogen ion concentration decreases (and vice versa). When measured on a logarithmic scale of 0
14, a pH of 0 is the highest acidity, a pH of 14 is the highest alkalinity, and a pH of 7 is neutral (Figure 2.11). Pure water is pH neutral, with seawater normally at a pH of 8 (mildly alkaline).