Wideband frequency select
The operator creates a single frequency echogram by suppressing all other frequency components from a wideband acoustic variable. The virtual variable has the equivalent single frequency data type of operand 1.
The pulse length is not adjusted in the calculation for this operator, so when used with Sv data, it will result in lower Sv values.
Echoview accepts operands of the following data types as input:
Operand 1 |
|
Settings
The Wideband Frequency Select Variable Properties dialog box pages include (common) Variable Properties pages and these operator pages:
Operands page
Wideband Frequency Select page
Settings |
Description |
Frequency (kHz) |
This is the center frequency in kHz for the virtual variable. |
Notes:
- The Wideband Frequency Select operator calculates the result using a 5kHz bandwidth. It will produce a result if the selected frequency is within the frequency range of the input data.
- No data samples in the operand are handled as -999 dB for use in Fourier calculations. See also Wideband frequency response note.
- Operand samples with values of -999 dB or 9.9e+37 dB are handled as (0,0i) in Fourier calculations.
- Sv, TS and TVG calculations use the operand's center frequency and the resultant frequency dependent absorption coefficient.
- The frequency displayed in the echogram's title bar is the center frequency, as the values used for the Sv and TS calculations remain the same all the way down the virtual variable chain.
- Frequency values can be specified using the LocalCal.
- Calculation precision when converting between dB and linear units
Algorithm
The band pass filter input is the data from operand 1, the specified Frequency and a fixed bandwidth of 5 kHz. The output data type is the single frequency equivalent of operand 1. The virtual variable retains the calibration of operand 1.