COM-S01R (All Models) Surface Units
11
WHAT TO EXPECT WHEN COMMUNICATING
UNDERWATER
Barriers to Transmission
Several factors can be barriers to sound transmission in the water.
Water density. Sound transmission can be interrupted by a change in water
density, most typically by the thermocline. (The thermocline is a layer of
water located typically within ten feet of the ocean surface; it has a markedly
different temperature than the water below ten feet.)
Important!: It must be understood that it is not always possible for
the Surface Unit transducer, if it is located over the thermocline, to
communicate with divers under the thermocline. In addition, if the
transducer is lowered below the thermocline, it should not be
allowed to touch the ocean floor.
Wave action or sea floor. Sound transmission can be reduced by wave
action at the surface, or by the sea floor.
Background noise. Sound transmission range can be reduced by
“background” noise, which is generated by a rough sea, by rain, by
biological noise such as a snapping shrimp, or by man-made noises such as
engines and high speed propellers.
Body shadow. Long-range sound transmission can be affected by the
position of the diver’s body in relation to the DIVELINK equipment. A range
reduction can occur if the diver’s body is in the line of sight between his/her
equipment and that of another diver or a Surface Unit.
This effect is known as body shadow. It is caused by the absorption of
sound by air inside the diver’s dry suit, or by air in the diver’s lungs. To
prevent body shadow, the diver should turn 45° so that the line of sight
between the DIVELINK equipment is restored.
Factors not affecting sound transmission. On the positive side,
underwater sound transmission is not affected by muddy or turbid water,
and is equally good in fresh and salt water.
