Konsberg EM 124, Руководство по установке

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Technical details
The EM 124 operates at sonar frequencies in the 10.5-13.5 kHz range. The transmit fan
is divided into 4 sectors in shallow modes (8 sectors in deep modes) to maximize range
capability but also to suppress interference from multiples of strong bottom echoes.
The sectors are transmitted sequentially within each ping, and uses distinct frequencies
or waveforms.
The nominal sonar frequency is 12 kHz with an angular coverage sector of up to 150
degrees and 1600 beams per ping. Achievable swath width on a flat bottom will normally
be up to 6 times (143 degrees) the water depth. The angular coverage sector is operator
controllable or may be set to a fixed range. It may also be set to vary automatically with
depth according to achievable coverage. This maximizes the number of usable beams.
The beam spacing is normally high density equidistant with equiangle available.
The transmit fan is split in several individual sectors with independent active steering
according to vessel roll, pitch and yaw. This place all beams on a “best fit” to a line
perpendicular to the survey line, thus ensuring a uniform sampling of the bottom and
100% coverage.
In dual swath mode the transmit fan is duplicated and transmitted with a small difference
in alongtrack tilt. The applied tilt takes into account depth, coverage and vessel speed to
give a constant beam separation alongtrack.
The sectors are frequency coded or have FM chirps, and they are transmitted sequentially
at each ping. The sector steering is fully taken into account when the position and depth
of each beam is calculated, as is the refraction due to the sound speed profile, vessel
attitude and installation angles. The pulse length and range sampling rate are variable
with depth (auto or manual) for best resolution.
In shallow waters due care is taken to the near field effects through nearfield focusing
individually applied in the different sectors.
EM 124 applies one focus range for each of the transmit sectors which are used for
shallow water environment. Dynamic beam focusing is used for the reception beams.
The ping rate is mainly limited by the round trip travel time in the water up to a ping
rate of more than 5 Hz.
The number of individual TX and RX modules in the two arrays depends on the chosen
configuration. The standard types identified by "transmission x reception" beamwidth
are:
•
0.5 x 1 degree system
: 96 transmit transducer modules and 16 receive transducer
modules
•
1 x 1 degree system
: 48 transmit transducer modules and 16 receive transducer modules
•
1 x 2 degrees system
: 48 transmit transducer modules and 8 receive transducer modules
•
2 x 2 degrees system
: 24 transmit transducer modules and 8 receive transducer modules
•
2 x 4 degrees system
: 24 transmit transducer modules and 4 receive transducer modules
•
4 x 4 degrees system
: 12 transmit transducer modules and 4 receive transducer modules
Kongsberg EM 124