noise.echogram {echogram}

Modelling ambient noise in echograms

Description

This function allows to estimate a model of the background noise in an echogram by fitting the equation proposed by De Robertis and Higginbottom (2007).

Usage

noise.echogram(echogram, ping = NULL, dB1m = NULL, alpha = NULL, plot = TRUE, out = FALSE)

Arguments

echogram

an object of class “echogram”.

ping

ping number for which the Sv values are to be modeled.

dB1m

noise level at 1m from the face of the transducer.

alpha

absortion coefficient of sound in sea water for echogram's frequency.

plot

logical. If TRUE (the default) a plot of the data and adjusted model is produced.

out

logical. If TRUE an echogram with the modeled noise is returned.

Details

The estimation of an ambient noise model for a particular acoustic frequency, eventually allows the “cleaning” of echograms by subtracting this noise.

Value

When plot = TRUE and out = FALSE (the default), only a plot is produced. With out = TRUE, the function returns an object of class “echogram” with the noise modelled.

Author(s)

Héctor Villalobos

References

De Robertis, A. and I. Higginbottom. 2007. A post-processing technique to estimate the signal-to-noise ratio and remove echosounder background noise 64:1282–1291.

Examples

# load echogram for noise estimation at 120 kHz (deep waters, no scatterers)
data("echo.noise")
attr(echo.noise$Sv, "frequency")
echogram(echo.noise, xref = "ping")

# a first look to the Sv values at ping 2
noise.echogram(echo.noise, ping = 2)

# To better adjust the model, we need to provide the absortion coefficient for 120 kHz and adjust
# the dB1m parameter. For this example, using data from a nearby CTD profile, alpha was calculated
# as being 0.03550554, while -131 dB is choosen for dB1m
noise <- noise.echogram(echo.noise, ping = 2, dB1m = -131, alpha = 0.03550554, out = TRUE)
echogram(noise)