R2Sonic 2026, Руководство по эксплуатации

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Page 175 of 254
Version 6.3 Rev r012
Date 05-11-2022
12.2.1 Salinity
Generally, salinity ranges from 32 – 38 parts per thousand (ppt) in ocean water. A change in salinity
will create density changes, which affect the velocity of sound. As a general rule, a change in salinity
of only 1 ppt can cause a sound velocity change of 1.4m/sec. There are many influences on the
salinity concentration in seawater.
1. Evaporation
2. Precipitation
3. Freshwater influx from rivers
4. Tidal effects (salt wedges)
12.2.2 Temperature
Temperature is the major influence on sound velocity in water. A 1°C change is equal to
approximately a 4m/sec change in velocity. Once the upper layer is passed, the temperature
normally decreases until the pressure becomes the more dominating influence on the velocity of
sound, which is approximately at 1000 metres. The normal influences on the temperature
component of sound velocity include:
1. Solar heating
2. Nighttime cooling
3. Rain/runoff
4. Upwelling
12.2.3 Refraction Errors
Refraction errors occur due to the wrong sound velocity profile being applied to the data. The error
increases away from nadir and, as such, is more apparent in the outer beams. The visual effect is
that the swath will curl up (smile) or curl down (frown). The actual representation is that the
soundings are either too shallow or too deep.
Figure 186: Refraction Error indication
At an angle of 45 ° in 10 meters of water, a ±10 meters per second velocity error will result in a depth
error on the order of ± 4.6 cm.
• Convex (smiley face) = Sound velocity profile used higher than the real profile
• Concave (frown face) = Sound velocity profile used lower than the real profile