An automated technique for estimating the signal-to-noise ratio and subtracting background noise
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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 technique page 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.
The authors 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).
Literature and other resources
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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
- 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
- Simmonds J and MacLennan D (2005) Fisheries Acoustics: Theory and Practice (Second Edition). Blackwell Publishing
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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
Echoview templates and documentation
Templates are saved as EV (Echoview) files and are named according to a defined naming convention.
Also view the notes sections of each template for further information:
- View > EV File Properties: Notes
- Object > Variable Properties: Notes
Template 1 - Alex De Robertis 
Description
This template is provided as supplementary information to De Robertis & Higginbottom (2007) by the authors.
View the data flow for this template.
Downloads
Echoview template version 4.90.48 (12 KB, 2nd Jun 2010)
Data (2.1 MB, 3rd Sep 2009)
Documentation (729 KB, 3rd Sep 2009)
Note: In version 5.1 onwards a 'Background Noise Removal' operator has been added to Echoview that replaces the above chain of 13 operators with a single, faster variable.
