BOUNCE

 

BOUNCE computes the reflection coefficient for a stack of acoustic media optionally overlying elastic media. The reflection coefficient is written to both a '.IRC' file (internal reflection coefficient) and to a '.BRC' file (bottom reflection coefficient).  These files can be used by KRAKEN, SCOOTER, and BELLHOP to provide a boundary condition, or plotted using PLOTRTH.

 

The input structure is identical to that used by KRAKENC although the input lines for source and receiver depth are not read and can be omitted.  Furthermore, the surface boundary condition is ignored and, in effect, replaced by a homogeneous halfspace where the incident wave propagates.

 

If you are interested in getting a reflection coefficient for a bottom which is being used in a KRAKENC, SCOOTER, or BELLHOP run, you will need to delete the layers corresponding to the water column.  Otherwise you will get a reflection coefficient corresponding to a wave incident from above the ocean surface.

 

The angles used for calculating the reflection coefficient are calculated based on the phase-velocity interval [CMIN, CMAX].  For a full 90 degree calculation set CMIN to the lowest speed in the problem (say 1400.0) CMAX to 1.0E9.  The actual number of tabulated points is then determined by RMAX.

 

If you are using the reflection coefficient for a coherent TL calculation then RMAX should be the maximum range to which you are propagating. The further you go, the finer the sampling that is needed in the reflection coefficient. Run time is usually not an issue; however, if you pick an RMax that is insanely large then it could be.


Note that a reflection coefficient depends on the impedance contrast between the halfspace from which the field is incident and the reflecting medium. Therefore BOUNCE must know the sound speed and other properties of the upper halfspace. If you're using the reflection coefficient to replace the sub-bottom in the ocean then you must set the speed of that upper halfspace to match the sound speed at the bottom of the ocean.


If you set the number of finite-difference grid points (NPTS) to zero, then BOUNCE automatically calculates a value to have 20 points per wavelength. If there is shear in a certain layer, then the shear wave will have a shorter wavelength than the P-wave speed. Then the smaller shear wavelength will be used to calculate the default. In some cases, 20 points per wavelength does not provide sufficient accuracy and you may need to increase that to as much as 100 points per wavelength.
 

Files:

 

        Name           Unit         Description

Input

        *.ENV            1       ENVironmental data

        *.BRC           10       Bottom   Refl. Coef.  (optl)

 

Output

        *.PRT            6       PRinT file

        *.BRC           10       Bottom   Refl. Coef.

        *.IRC           12       Internal Refl. Coef.

 

 

EXAMPLE OF ENV FILE:

 

'Refl. coef. test problem'

50.0

1

'NAW'
0.0  1500.0  0.0  1.0 0.0 0.0/        ! Z(m) CP CS (m/s) RHO (g/cm3) AP AS
100 0.0 20.0

    0.0 1600.0 400.0 1.8 0.2 0.5

   20.0 /

'A' 0.0

   20.0 1800.0 600.0 2.0 0.1 0.2

1400.0 19000.0

10.0                  ! RMAX (km)

1                     ! NSD

50.0 /                ! SD(1:NSD)

501                   ! NRD

0.0 150.0 /           ! RD(1:NRD)

 

 

The above example (taken from the SAFARI reference manual) involves two elastic layers.