Extract Bottom Feature

This operator extracts a Bottom Classification feature from an acoustic variable with a specified Bottom line under Bottom settings on the Analysis page of the Variable Properties dialog box.

The output is virtual bottom feature line data that may be viewed as a table, graph or export .csv file. The Extract bottom feature virtual variable is supported by live viewing.

Operand 1

Complex Sv
Pulse compressed complex SvS
Sv

Settings

The Extract Bottom Feature dialog box pages include (common) Variable Properties pages and these operator pages.

Operands page

Display page

Name and Notes page

Bottom Feature page

Feature Extraction Interval

Time/distance grid mode specifies the horizontal interval type used by the bottom classification calculations. The time/distance/ping list offers the following interval types:

Time in (min) or (hours) or (days)
GPS distance (nmi) or (m)
Vessel log distance (nmi) or (m)
Water current distance (m)
Ping number

Enter the Time per interval or Distance per interval or Number of pings per interval. This is the calculation interval for the bottom feature.

For further information about the feature extraction interval refer to Bottom classification algorithms - Feature extraction interval.

Select Start interval numbering from the first ping outputs intervals that are number from the first ping in the operand.

Clear the setting to base the interval numbering from the operand's Grid page settings. For example, a transect starting at interval 4 will label the first analysis interval as 4.

Feature To Extract

Select a single bottom feature to extract:

Bottom_roughness_normalized
Bottom_hardness_normalized
First_bottom_length_normalized
Second_bottom_length_normalized
Bottom_rise_time_normalized
Bottom_line_depth_mean
Bottom_max_Sv
Bottom_kurtosis
Bottom_skewness

Notes:

Bottom_max_Sv, Bottom_kurtosis, Bottom_skewness are associated with the first bottom echo. These features may reveal useful characteristics of the roughness index that is used to calculate Bottom_roughness_normalized.
When no second bottom echo exists, the calculation for Second_bottom_length_normalized and Bottom_hardness_normalized can't be evaluated.
See also: About bottom classification, Bottom classification algorithms.