ERAS Sonar Test System - Low Frequency

ERAS Low Frequency Overview

What is ERAS?

eras sonar calibration test and training system — ERAS sonar calibration test and training system

Chelsea Technologies’ Echo Repeater Acoustic Source (ERAS) is a self-contained sonar calibration, test and training system for use on small vessels. An included ruggedised laptop computer is used to provide all signal selection and control, via a bespoke graphical user interface that can be easily operated, without the need for specialist training.

“a self-contained sonar calibration, test and training system for use on small vessels”

The only other units are a deck unit containing the signal conversion and amplification and a hand-deployable transducer. The system is useful for testing active and passive sonar range, bearing accuracy and target identification. Two frequency bands are offered in the standard ERAS system:

Band 1 Low Frequency (LF) – 3 kHz to 23 kHz
Band 2 High Frequency (HF) – 23 kHz to 50 kHz
There is also a low frequency variant – 280Hz to 2600Hz

ERAS can transmit at up to 171 dB re 1 µPa@1m with a flat transmit response to within ±1.5 dB across these two frequencies bands. The LF source level can be increased to 180 dB re 1µPa@1m between 7 kHz and 19 kHz.

Dual Band Acoustic Source – part of Chelsea Technologies’ acoustic design heritage

Dual Band ERAS Transducer in Transit case — Dual band ERAS transducer in transit case

As a calibrated acoustic transmitter (source mode) ERAS can generate complex test signals. This mode is aimed at testing passive sonar. The test signals can also be used to simulate some active sonar pings and approximate acoustic signatures of known targets by combining noise and tones. An external input is also provided for replaying pre-recorded acoustic signatures through the system. In summary:

Up to 24 tones and 5 bands of band limited noise (white, pink or PRN)
- Each with a selectable source level and frequency
- Each tone selectable as pulsed or CW
AM or FM modulated Signals, (24 Tones and 5 bands of band limited
noise)
Sweeps, LPM or LFM
Pulse trains up to 1000 pulses with stepped source level
Broadband noise (white, pink or PRN)

Dual Band Echo Repeater – part of Chelsea Technologies’ acoustic design heritage

The Echo Repeater Acoustic Source - Transducer Deck Cable — The echo repeater acoustic source – transducer deck cable

In “Echo Repeat” mode, ERAS can repeat signals received from a hydrophone contained in the hand-deployable, transducer head. It does this in response to a trigger event, based either on the incoming acoustic signal, an external input, or under operator control. The repeated signal can have a highlight structure imposed upon it to mimic the reflections from a target. A programmed sequence of echo repeated signals can be configured to simulate a moving target by appropriate addition of Doppler frequency shift and monotonically changing time delay. A transpond pulse can also be tagged onto the signal to indicate that the sonar ping was detected and repeated. This function is used to calibrate active sonar systems by providing a controlled acoustic target.

ERAS Low Frequency Features

ERAS Sonar Test System – Low Frequency Features:

Compact and lightweight system, ideal for transportation
Hand deployable from a range of ocean vessels
Acoustic source and echo repeat functions for generating and receiving signals
Part of Chelsea’s heritage in marine sonar test systems

ERAS Test System – Low Frequency Applications:

Sonar test and calibration
Underwater target detection
Sonar operator training
Surveillance
Noise signature simulation
At sea, acceptance trials

Low Frequency Operating Modes:

Complex Signal Source
Sequence
Echo Repeater
Transponder
Received Signal Monitor
Slant range Measurement

ERAS Low Frequency Specifications

ERAS Low Frequency Source Modes:

Source Transmit Generation Bandwidth 280Hz to 2600Hz
Pulse Lengths 3ms to 10s or CW
Number of Pulses Up to 1000
Pulse Intervals Up to 60s
Variable Step Levels -10 to +10 dB
Tones Up to 24 (each with definable source levels & frequencies – CW or pulsed
Sweeps LFM or LPM
Noise Either Broadband or up to 5 user definable bands
Noise Types White, Pink or Pseudo-Random
Modulated Signal AM or FM, user definable carrier and modulating
signal

ERAS Low Frequency Transpond Modes

Frequency Range 280Hz to 2600Hz
Pulse Length 0.010s to 10.00s (0.001s step)
Variable Step Levels -10 to +10 dB
Trigger Types Acoustic, TTL pulse or manual
Trigger Level & Averaging Fully user definable
Transpond Types LFM or LPM sweep, Monotone or Source Mode

ERAS Low Frequency Operating Modes: