Block II: OASP options

The significance of the single-letter OASSP options are:

C

Creates an representation of the field in the form of contours of integration kernels as function of horizontal wavenumber (slowness if option B is selected) and frequency (logarithmic y-axis). All axis parameters are determined automatically.

G

Rough interfaces are assumed to be characterized by a Goff-Jordan power spectrum rather than the default Gaussian.

H

Horizontal (radial) particle velocity calculated.

J

Complex wavenumber contour. The contour is shifted into the upper halfpane by an offset controlled by the input parameter COFF (Block III). NOTE: If this option is used together with automatic sampling, the complex frequency integration (option O) is disabled, allowing for computation of complex CW fields or transmission losses (plotted using PP).

K

Computes the bulk stress. In elastic media the bulk stress only has contributions from the compressional potential. In fluid media the bulk stress is equal to the negative of the pressure. Therefore for fluids this option yields the same result as option N or R.

L

Linear vertical source array.

N

Normal stress (=-p in fluids) calculated.

O

Complex frequency integration contour. This new option is the frequency equivalent of the complex wavenumber integration (J option in OAST). It moves the frequency contour away from the real axis by an amount reducing the time domain wrap-around by a factor 50 [3]. This option can yield significant computational savings in cases where the received signal has a long time duration, and only the initial part is of interest, since it allows for selection of a time window shorter than the actual signal duration. Note that only wrap around from later times is reduced; therefore the time window should always be selected to contain the beginning of the signal!

P

Plane geometry. The sources will be line-sources instead of point-sources as used in the default cylindrical geometry.

R

Computes the radial normal stress (or for plane geometry).

S

Computes the stress equivalent of the shear potential in elastic media. This is an angle-independent measure, proportional to the shear potential, with no contribution from the compressional potential (incontrast to shear stress on a particular plane). For fluids this option yields zero.

T

The new option `T' allows for specification of an array tilt in the vertical plane containing the source and the receivers. See below for specification of array tilt parameters.

U

Decomposed seismograms. This option generates 5 transfer function files to be processed by PP:

File name	Contents
input.trf	Complete transfer functions
input.trfdc	Downgoing compressional waves
input.trfuc	Upgoing compressional waves
input.trfds	Downgoing shear waves alone
input.trfus	Upgoing shear waves

V

Vertical particle velocity calculated.

Z

Plot of SVP will be generated.

d

Radial Doppler shift is accounted for by specifying this option, 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). Since this option requires incorporation of the source function in the wavenumber integral, the PP post-processor must be used with source pulse -1 (impulse response).

f

Full Bessel function integration. This new option does not apply the asymptotic representation of the Bessel function in the evaluation of the inverse Hankel transforms. The implementation is very efficient, and the integral evaluation is performed just as fast as the asymptotic evaluations. It is more sensitive to truncation, however, and therefore usually requires a much larger wavenumber interval to avoid truncation arrivals. Further, the Bessel function represents both outgoing and incoming waves, such that the periodicity of the discrete integral transforms introduces false arrivals from the periodic sources. It is therefore recommended to solely apply this option for cases where very steep propagation angles are important, e.g. short offset VSP computations. For all other cases the asymptotic Filon (option F) is highly recommended.

g

Rough interfaces and volume inhomogeneities are assumed to be characterized by a Goff-Jordan power spectrum rather than the default Gaussian (Same as G).

l

User defined source array. This new option is similar to option L in the sense that that it introduces a vertical source array of time delayed sources of identical type. However, this option allows the depth, amplitude and delay time to be be specified individually for each source in the array. The source data should be provided in a separate file, input.src, in the format described in Section 8.5.3.

p

The perturbed Green's functions will be used for the waveguide propagation of the scattered field. This corresponds to applying scattering loss to the propagation and therefore constitutes a higher order scattering term, representing multiple scattering. In general p will yield a lower bound for the scattered field, while the default yields an upper bound. Option p has no effect for volume scattering, which is always computed in the Born approximation.

s

OASSP will compute the scattered field perturbation alone. By default the total field will be calculated.

t

Eliminates the wavenumber integration and computes transfer functions for individual slowness components (or plane wave components). The Fourier transform performed in PP will then directly compute the slowness/intercept-time or response for each of the selected depths. When option t is selected, the range parameters in the data file are insignificant.

v

As option l this option allows for specifying a non-standard source array. However, it is more general in the sense that different types of sources can be applied in the same array, and the sources can have different signatures. The array geometry and the complex amplitudes are specified in a file input.strf which should be of trf format as described in Section 8.5.3.

#

Number (1-5) specifying the source type (explosive, forces, seismic moment) as described in Section 8.5.3