General Description; The Transceiver; The Signal Processing; Power Budget - Simrad EY500 Instruction Manual

Portable scientific echo sounder

Table of Contents

Theory of operation

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.

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.

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.

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

P3403E/A

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