echoview

Background Noise (1): Single Beam

Removing background noise by subtracting a time-varying noise estimate

Contents
# Background information
# Links to literature and other resources
# Echoview templates and documentation
# Link to this technique on the Hydroacoustics User Forum

Related links
> About data-processing procedures and techniques
> Share techniques and/or templates
> Disclaimer

Keywords
Background-noise removal; single-beam echosounder; scrutinization; post-processing; scrutiny; signal-to-noise ratio; SNR; echo integration; effective data range

Background information

How does the technique work?

This is based on the published technique by De Robertis & Higginbottom (2007). The background-noise level is automatically estimated from the data itself and subtracted from the raw signal. De Robertis and Higginbottom calculate the noise estimate for a user-defined time period as the minimum sample power value during that period, where the data are first resampled into bins with dimensions on the order of 20 pings in the horizontal and 10 m in range.

What does the technique achieve?

This technique enables you to obtain usable data from samples with a low signal-to-noise ratio (SNR), e.g. weak scattering targets such as krill detected towards the maximum effective range of the transducer. It also enables you to calculate the SNR of each sample, and thereby make an objective decision as to which data to reject on the basis of a threshold SNR.

Definition of background noise

Simmonds and MacLennan (2005) define signal as transmitted sound backscattered onto a transducer, and noise as all other contributions to the acoustic energy received. Background noise is generally understood to refer to noise of a lower amplitude (around -140 dB) that persists for longer (on the order of minutes or longer), while intermittent noise refers to higher-amplitude noise (around -90 dB or more) that lasts for only a short time (on the order of seconds).

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Literature and other resources

Journal articles, reports etc.

• De Robertis A and Higginbottom I (2007) A post-processing technique to estimate the signal-to-noise ratio and remove echosounder background noise. ICES Journal of Marine Science, 64: 1282-1291
  
• Korneliussen RJ (2000) Measurement and removal of echo integration noise. ICES Journal of Marine Science, 57: 1204-1217
• Watkins JL and Brierley AS (1996) A post-processing technique to remove background noise from echo-integration data. ICES Journal of Marine Science, 53: 339-344
• Nunnallee EP (1990) An alternative to thresholding during echo-integration data collection. Rapports et Proces-verbaux des Reunions du Conseil International pour l'Exploration de la Mer, 189: 92-94

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Echoview templates and documentation

Please read about the Echoview-template naming convention here.

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