depths of 1000 meters (3000 feet). It is suitable for mid-size ROV. The surface station is
connected to a Microsoft Windows PC running the DiveBase software.
Figure 1.1 shows how PILOT works. The surface station is on the boat. The three cabled sonar
transducers (acoustic antennas) are lowered over the side. The ROV transponder is mounted on the
underwater vehicle.
Figure 1.1: Target Position Determined By ‘Short Baseline’ Method
To find the ROV position, the surface station will transmit an interrogate signal (two pings) through
transducer #1. This signal travels through the water and eventually reaches the ROV mounted
transponder, which replies with a message that includes its current depth. The reply travels back to
all three surface station transducers. The surface station now measures the time elapsed between
the transmission of the interrogate and the reception of the ROV reply at transducers #1, #2 and #3.
Because the speed of sound in water is fairly well known, these signal run times are easily converted
into distances (d1, d2, d3). Finally, a little trigonometry yields the position of the ROV.
This method of tracking is commonly known as short baseline tracking. The word ‘baseline’ refers to
the imaginary lines that connect the sonar transducers at the surface. The baseline is the reference
for navigation. It is helpful to remember a few characteristics of short baseline tracking.
Characteristics PILOT 'Short Baseline' Tracking
●
PILOT shows the position of the target (ROV) relative to the position of the boat or more
specifically relative to the location of the three surface station sonar transducers. If the
boat rotates, the target will appear to move in a circle around the tracking screen.
●
PILOT measures the distance of the target with a repeatability of about 0.15 meters,
independent of how far the transducers are spaced apart.
