Background Noise Estimation

This operator estimates the background noise level. Background noise manifests as a 'TVG rainbow' on an echogram.

The operator is based on the algorithm and definitions described in De Robertis and Higginbottom (2007).

Notes:

See also: The Data thresholding section on the Noise, background object and signal removal in Echoview page.
See also: The Effect of No data samples on the Wideband Frequency Response graph page.
The output unit for wideband operands is the corresponding continuous wave unit. See also: Wideband considerations.
When the estimated noise is greater than the signal, Echoview outputs a value of no data.
TVG is not applied at ranges less than 1 meter from the transducer.

Echoview accepts operands of the following data type as input:

Complex power dB
Complex Sv
Complex TS
Multibeam Sv
Multibeam TS
Power dB
Pulse compressed complex power dB
Pulse compressed complex Sv
Pulse compressed complex TS
Sv
TS

Settings

The Background Noise Estimation Variable Properties dialog box pages includes (common) Variable Properties pages and these operator pages:

Operands page

Background Noise Estimation page

The following settings are used to configure the Averaging cell for this operator.

Note: If the calibration of the selected beam differs from that of beam 0 then the correct values should be supplied using an ECS file. Unintended values may otherwise result.

Settings	Description
Horizontal extent (pings)	Specifies the horizontal size of the averaging cell (number of pings). The cell width defines an averaging ping interval that examines samples for the noise estimate for the middle ping of the interval. The default value is 20 pings. The value is cited in the Sensitivity to grid size discussion in De Robertis and Higginbottom (2007).
Vertical units	Specifies the units for the vertical axis of the averaging cell. Available units are Samples or Meters. Notes: Under Meters, a value for samples per meter is evaluated once (only), for the first group of calibrated pings and is applied to all pings in the echogram. In the case where the ping calibration changes within the data, the evaluated value may be inaccurate. Meters are used in De Robertis and Higginbottom (2007).
Vertical extent (samples) Vertical extent (meters)	Specifies the vertical size of the averaging cell. Notes: De Robertis and Higginbottom (2007) use a vertical cell size of 10 m for their data. The number of samples within the Vertical extent of the averaging cell can affect the statistics of the noise estimate. Too few samples may result in a poor noise estimate. Be aware that too few samples may result in a poor noise estimate.
Vertical overlap (%)	Specifies the percentage vertical overlap of the averaging cell down the samples of the averaging ping interval. Notes: The default overlap is zero. De Robertis and Higginbottom (2007) use non-overlapping averaging cells. Calculation time increases with an increase in Vertical overlap. The maximum overlap that can be entered is 99%. Specify an overlap when the calculated noise estimate is too high and erodes the wanted signal. Echogram results may change for dataflows that use Vertical overlap (%) due to a fix for this setting from Echoview 10.
Apply TVG to output	Applies time varied gain (TVG) to the Sv or TS output of the background noise estimation variable. The setting is selected by default for new virtual variables. When TVG is not added to the output, the background noise estimation Sv or TS value is similar to a single Powercal value per ping.

Algorithm

For the pings in an interval k, the background noise is estimated as

The term on the right-hand side of the equation is the minimum of the averaged Power_cal value computed for each ping interval.

Power_cal is nominally the logarithmic measure of received power (adjusted for the echosounder-specific calibration coefficients) used in echo integration.

For full details refer to the Estimate the noise section of the Background Noise Removal operator page and De Robertis and Higginbottom (2007).

Background Noise Estimation

Settings

Operands page

Background Noise Estimation page

Algorithm

See also