FRC is the source center frequency. As the source convolution is performed in PP, FRC is not used in OASSP, except for cases involving moving sources (option d), but will be written to the transfer function file and become the default for PP.
COFF is the complex wavenumber
integration
contour offset. To be specified in
,
where
is the wavelength at the source
depth SD. As only the horizontal part of
the integration contour is considered, this parameter
should not be chosen so large, that the amplitudes
at the ends of the integration interval become
significant. In lossless cases too small values
will give sampling problems at the normal modes
and other singularities. For intermediate values,
the result is independent of the choice of COFF,
but a good value to choose is one that gives 60 dB
attenuation at the longest range considered in the FFT, i.e.
Doppler shift
By specifying option d in OASP V.1.7 and higher, radial Doppler shift is accounted for using the theory developed by Schmidt and Kuperman [9]. The source pulse and the radial projections of the source and receiver velocities must be specified in the input file following the specification of the centre frequency and the contour offset (Block II), i.e.
| Standard | For option d |
| FRC COFF | IT VS VR |
IT is a number identifying the source pulse as described in Sec.16. VS and VR are the projected radial velocities in m/s of the source and receiver, respectively, both being positive in the direction from source to receiver. Since this option requires incorporation of the source function in the wavenumber integral, the PP post-processor must subsequently be used with source pulse -1 (impulse response).