Page 60 - The ROV Manual - A User Guide for Remotely Operated Vehicles 2nd edition

48 CHAPTER 2 The Ocean Environment
Low water
High water
To High moon
water
FIGURE 2.15
Low water
Tidal movement in conjunction with planets.
On a vertical profile, the tide may interact with the general flow pattern from a river or estuary—the warm fresh water may flow from a river on top of the cold salt water (a freshet, as mentioned above) as the salt water creeps for a distance up the river. According to Van Dorn (1993), fresh water has been reported over 300 miles at sea off the Amazon. If a brackish water estuary is the operating area, problems to be faced will include variations in water density, water flow vector/speed, and acoustic/turbidity properties.
2.3.1.3 Water velocity
Water velocity is the measure of the speed at which water travels, or the distance it travels over a given time, and is measured in meters per second. Hydrologists and other researchers measure water velocity for monitoring current in rivers, channels, and streams, to measure the effect of ves- sel traffic in harbors and ports, and to calculate water flow. To account for drift, water velocity readings are key factors in knowing where and when to deploy buoys and other environmental devices to ensure their correct location.
2.3.1.4 Waves and the Beaufort scale
Most operations manuals will designate launch, recovery, and operational parameters, as they relate to sea state, which is measured in the Beaufort scale (Table 2.5). Waves are measured with several metrics, including wave height, wavelength, and wave period. Wave height, -length, and period depend upon a number of factors, such as the wind speed, the length of time it has blown, and its fetch (the straight distance it has traveled over the surface).
Energy is transmitted through matter in the form of waves. Waves come in several forms, including longitudinal, transverse, and orbital waves. The best example of a longitudinal wave is a sound wave propagating through a medium in a simple back and forth (compression and rarefac- tion) motion. A transverse wave moves at right angles to the direction of travel, such as does a
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To moon