Teledyne SeaBat T Series Operator's Manual page 50

ACTIVE SONAR USAGE
In each mode (except FlexMode), the surveyor may choose
the number of beams to be formed by using a slider. In Equi-
Distant mode, an additional option is available which allows
the surveyor to set the desired seafloor spacing with the
slider. The system automatically detects the depth and sets
the spacing as required by the surveyor. Adjustments may
take place during survey: there is no requirement to interrupt
the survey.
There is always a minimum number of beams that theoretically ensures "100% insonification" of
the swath, which roughly speaking means that there are no gaps between beams; in other words,
each beam adjoins or slightly overlaps its neighbor. IHO specifications no longer refer to the term
"100% insonification", as it cannot ever be proved conclusively; it is accepted that the situation
may arise where "100% insonification" is not achieved.
6.2.9.1 Equi-Distant, Equi-Angle, and Intermediate Modes
 Equi-Distant mode: Up to 140°/150° coverage angle. Typically the default mode for
general purpose surveys where it is critical to maintain a certain number of hits per
cell across the maximum possible swath. Provides high-density equidistant soundings
across the entire swath.
 Equi-Angle mode: Up to 165° coverage angle. Typically used for tilted heads to
inspect upwards, water column data recording, or for minimizing the amount of data
being recorded. Provides an equiangular distribution with the fewest beams.
 Intermediate: Up to 140°/150° coverage angle. Designed for general purpose
surveys, tilted head modes, or dual-head operations. Provides high-density soundings
over the entire swath.
In Equi-Distant mode the spacing is modified to maintain an equal horizontal distance between
soundings on the seafloor assuming a flat bottom and in Equi-Angle mode the beam center-
center angular spacing is constant across the swath. It is recommended that Equi-Distant mode
be used for general survey applications where the requirement to achieve a specific number of
sounding per cell in the across-track is critical, or where the seafloor is generally flat.
When surveying features such as wrecks and vertical structures such as harbor walls,
Intermediate or Equi-Angle mode should be used in preference to Equi-Distant mode. In extreme
conditions, using Equi-Distant mode over complex structures can cause magnified artifacts due to
the large overlap between beams towards the edge of the sector.
In short, these are the pros and cons for the three modes, keeping in mind that in each case the
negative effect is much more dramatic with a wide swath (see also section 7.2.2 Equi-Distant,
Equi-Angle, and Intermediate Modes):
 Equidistant spacing:
o Constant spacing even at large
 Equiangular spacing:
o Low number of beams
 Intermediate (compromise):
o Moderate beam number
o Moderate spacing at large angles
SeaBat T-Series Subsea Operator's Manual
Version 7
PRO
angles
o Very large number of beams
o Very wide spacing at large angles
Page 38
CON
January 31, 2019