Simrad EY500, Instruction Manual

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Theory of operation
P3403E/A
5
1 INTRODUCTION
1.1 GENERAL DESCRIPTION
The EY 500 system performs bottom detection, echogram generation and echo
integration, and for split-beam systems also target strength statistics are
estimated. This section gives some theory behind this performance.
1.2 THE TRANSCEIVER
The transceiver contains transmitter, receiver and A/D-conversion circuitry.
The receiver does not contain any TVG (Time Varying Gain) function as the
EY 500 carries out this function solely in software. Instead, the receiving system
is designed as a "power meter" with a large instantaneous dynamic range. Input
power levels from -160 dBW to 0 dBW (dB’s relative 1 W) are measured to a
precision of a fraction of a dB and are output to the signal processor as 16-bit
digital words using the dBW scale for numeric representation. The receiver
includes one receiving channel for single-beam operation and four matched
channels plus phase measurement circuitry for split-beam operation.
1.3 THE SIGNAL PROCESSING
The signal processing is done by software in the PC. It takes care of control of
the transmitter/receiver and processing of received data.
The software generates echograms, and estimates physical parameters (depth,
volume backscattering strength, target strength etc) from the received signal
samples by taking into account instrumental effects, transmission losses and
transmitted power.
2 POWER BUDGET
The EY 500 utilizes a sophisticated receiver design which is characterized by a
very high amplitude measurement accuracy over the entire dynamic input range
(-160 dBW to 0 dBW). The absolute power level of the received signal is
measured enabling the EY 500 to estimate volume backscattering strength and
target strength in the absolute sense. The estimation algorithm is based on a
physical model which accurately accounts for instrumental effects and
propagation losses. This model will be outlined in order to assure that the
measured output scattering parameters are correctly interpreted.
The radiation and receiving properties of a transducer is traditionally stated in
terms of source level, directivity index, receiving response etc. However, the