Best bottom candidate settings
The Best candidate bottom detection algorithm settings can be used to pick an editable bottom line or virtual bottom line for an echogram. The default settings can be optimized to produce a better line pick for your data.
The Best candidate bottom detection settings are entered:
- For an editable line under the Single beam tab on the Lines and Surfaces page of the EV File Properties dialog box.
- For a virtual line on the Best bottom candidate line pick page of the Line Properties dialog box for a virtual line created with the Best bottom candidate line pick operator.
The following settings are available:
|
Setting |
Units |
Default |
Description |
Decrease setting... |
Increase setting... |
|
Minimum Sv for good pick |
dB re 1m-1 |
-70.0 |
If the peak maximum of the candidate peak is less than this value then the bottom line status is set to BAD. |
to ignore weak echoes. The picked bottom line will have fewer segments with a BAD line status. |
to highlight weak echoes. The picked bottom line will have more segments with a BAD line status. |
|
Discrimination level |
dB re 1m-1 |
-50.0 |
The value at which the bottom depth is found on the candidate peak. The bottom depth is the intersection of the Discrimination level with the rise side of the peak. For more information refer to Step 6 of the algorithm. |
to exclude more bottom signal. |
to include bottom-hugging biomass. |
|
Backstep range |
m |
-0.5 |
The offset above the Discrimination level. For more information refer to Step 6 of the algorithm. |
to decrease the offset above the bottom signal. |
to increase the offset above the bottom signal. |
|
Peak threshold |
dB re 1m-1 |
-50.0 |
Samples with values greater than the Peak threshold are considered to be part of a candidate peak. |
if the echoes in the echogram are weak. |
if the echoes in the echogram are strong. |
|
Maximum dropouts |
samples |
2 |
The maximum of number of contiguous samples in a candidate peak allowed to fall below the Peak threshold. More than one group of dropouts can occur in a peak. |
if the signal to noise ratio for the echogram is high. |
if the signal to noise ratio for the echogram is low. |
|
Window radius |
samples |
8 |
The distance on either side of the range for a candidate peak that is searched in the adjacent ping. For more information refer to Step 2 in the algorithm. |
if the bottom is smooth and flat, or the ping rate is high. |
if the bottom is erratic or steep, or the ping rate is low. |
|
Minimum peak asymmetry |
None |
-1.0 |
The ratio of a measure of the gradients of the rise and decay sides of the candidate peak. Candidate peaks that have a ratio less than the Minimum peak asymmetry are rejected. |
if no spurious bottom is detected. |
if spurious bottom is detected. Try values around 0.05. |
See also
About the Best bottom candidate line pick
Best bottom candidate line pick algorithm