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.
'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.