Edgetech Model 3100P Sub-bottom Sonar System, Hardware Manual

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2-7
a. Vertical resolution is the smallest distinguishable distance between the peaks of two reflections
that can be displayed on the screen as separate reflectors. Sound energy is reflected back to the
sonar system when the transmitted pulse encounters a change in density. The resolution of a
sonar system is measured by its ability to distinguish between two adjacent targets. The vertical
resolution is dependent on the transmitted chirp pulse bandwidth. It is theoretically calculated by
the product of the transmitted pulse length (inverse of the bandwidth) and half the speed of
sound in water (approximately 750 m/s). For example, a full bandwidth pulse from an SB-424 Tow
Vehicle has a vertical resolution of 3.75 cm (1/20,000 x 750).
b. The value for sub-bottom penetration is the maximum distance beneath the sea floor that a step
change of 10% in density can be seen on the sub-bottom display. This assumes that the sediment
is gas free (no organic materials), that the lowest frequency of the pulse spectrum is transmitted
and that the vehicle is within 5 meters of the seabed (range for maximum penetration). Lower
frequencies reduce attenuation (absorption of sound). Towing the vehicle close to the sea floor
reduces the acoustic footprint thereby reducing scattering (interfering reflections) from the sea
floor and within the sediments.
c. At the -3 dB points, depending on the center frequency.
2.2 Mechanical Drawings
The following pages contains Drawings for the SB-216 and SB-424.