Transient Noise Ping Removal
This operator identifies pings which show an amplified signal strength when compared to the surrounding pings, typically associated with transient noise.
The operator is based on the "attenuated signal filter" algorithm and definitions described in Ryan et al. (2015).
It accepts operands with the following data types:
- Complex power dB
- Complex Sv
- Complex TS
- Power dB
- Pulse compressed complex power dB
- Pulse compressed complex Sv
- Pulse compressed complex TS
- Sv
- TS
- Unspecified dB
This operator compares the values of the samples in a given ping Vij at the Pth percentile against the values of the samples in its adjacent pings Vmn at that percentile.
If the difference between Vij and Vmn exceed a given ThresholdAmplified signal, the operator replaces that ping with No data, or the value as a percentile of the row of samples at the intersection between Vij and Vmn.
For a full description of the algorithm, refer to the Context window for attenuated signal detection and sample replacement section of the Attenuated Signal Removal page.
Also refer to the Notes section below for more information on this operator.
Settings
The Transient Noise Ping Removal Variable Properties dialog box pages include (common) Variable Properties pages and these operator pages:
Operands page
Transient Noise Ping Removal page
Detection
|
Exclude above |
Choose an exclusion line (refer to Exclude-above and Exclude-below lines) from the drop-down menu. The operator will ignore ping samples above this line. |
|
Exclude below |
Choose an exclusion line from the drop-down menu. The operator will ignore ping samples below this line. |
|
Context window size (pings) |
Specify an odd number of pings in the context window (refer to Context window for attenuated signal detection and sample replacement). Default 31. The algorithm compares the ping in the center of this window, against the other pings in this window to determine if the samples in a particular ping are noise. |
|
Percentile |
Percentile level for the pings in the context window (excluding the center ping). This value corresponds to what you deem to be the base signal level. Samples in the center ping which exceed this value are tested against the Threshold (below) to determine if they are noise. |
|
Threshold |
Ping samples in the center ping that exceed the percentile by this value are treated as transient noise. Default 10. |
Replacement
|
Replacement value |
The operator replaces pings which meet the noise criteria by this value. Choose between
|
|
Percentile |
Specify the value for the Percentile option for the Replacement value. |
Notes
- It is advised to use great care with this operator because legitimate biological and bottom signal can be mistakenly changed. Study your echogram data and use the Exclusion settings Exclude above and Exclude below to protect legitimate data. The use of no data as a Replacement method may be able to visually highlight where legitimate data is adversely affected by this operator. After studying their data Ryan et al reason that TVG amplification of transient noise is not significant at depths above 250m and that the biological echo is strong above 250m and may be mistakenly identified as transient noise.
- No data samples within the Context Window are not used in percentile calculations and are not replaced.
- The operator algorithm may fail to identify amplified noise in the set of start and end pings of the echogram. This is due to the handling of boundary samples with respect to the Context window. To address this issue, you can inspect the set of first and last pings and use regions and/or advanced operators to deal with manually identified amplified noise.
- In Ryan et al (2015), transient noise sample values are replaced with "no data". The algorithm offers two noise sample replacement methods, No data or Percentile of samples in the Context Window.
- Transient noise example.
- Samples in adjacent pings may shift in depth under heave compensation and this may affect the amplified noise.
- In Ryan et al (2015) TS and complex data are not considered.
- Complex and pulse compressed complex acoustic variables are largely handled in a manner similar to single frequency power, Sv or TS variables. When a new sample value is required, it is assumed that the complex phase for the sample is unchanged and the complex magnitude of the sample is calculated as for ComplexMagnitudeNew.
- 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.
See also
About virtual variables
Background noise in Echoview
Background noise calculation on the Analysis page