8.5.2 Time of Flight Probe
The Time of Flight probe incorporates a transducer that transmits an acoustic pulse that reflects
back from a plate that it is at a very precise distance from the transducer. The two-way travel time
is measured, divided by 2, and the sound velocity determined. The Time of Flight probe is usually
considered more accurate for multibeam survey work.
The sound velocity probe that is mounted close to the Sonic 2024/2022 sonar head is a time of flight
probe.
Figure 124: Time of Flight SV probe
8.5.3 XBT Probes
The XBT is a probe which free falls through the water column at a more or less constant speed (the
probe is designed to fall at a known rate so that the depth can be inferred) and measures the
temperature as it passes through the water column. Inside the probe is the thermograph, which is
attached to a spool of very fine wire. Two very small wires transmit the temperature data from the
probe back to a computer. The XBT is not recovered. XBT probes can be launched whilst underway
for depth
Plate
Page 117 of 210
Version 5.0 Rev r002
Date 05-08-2014
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