Page 416 - The ROV Manual - A User Guide for Remotely Operated Vehicles 2nd edition

(a)
ROV with scanning sonar
(b)
Sonar in polar scan
15.2 Sonar types and interpretation 409
FIGURE 15.20
(c)
Sonar in sector scan
(d)
Sonar in sector scan with 90° train
Scan modes of a mechanically scanning sonar system with (a) profile view, (b) plan view of polar mode, (c) sector scan, and (d) sector scan with train.
15.2.4 Single-/dual-/multifrequency versus tunable frequency
The single-/dual-/multifrequency, CHIRP, and tunable sonars all have their advantages and disad-
vantages. Definitions and discussion for each follows:
1. Single frequency: The single-frequency sonar system transmits and receives on one frequency and is the simplest sonar design due to its transducer selection on its nominal resonance frequency. Unfortunately, only a limited amount of target data can be ascertained from the use of a single-frequency backscatter analysis.
2. Dual frequency: This system arrangement allows gleaning of differing data parameters from the same target area based upon simultaneous or alternating transmissions of dual-frequency acoustic beams, generating each frequency’s backscatter characteristics of the sample area.
An excellent example of the advantages of dual-frequency sonar systems came recently during an oil spill in the Gulf of Mexico. A barge filled with heavy (heavier than water) heating oil struck a submerged unmarked platform destroyed by one of the storms of 2005. The oil sank to the bottom, requiring various governmental agencies to track the plume. To discriminate the submerged oil plume from the loosely consolidated mud bottom, a dual-frequency