KRAKEN is the main program. It takes an environmental file, computes the modes, and writes them to disk for use by other modules. A print file is also produced, echoing the user input.
KRAKENC is a complex arithmetic version (hence the C in KRAKENC) of KRAKEN. By working in the complex domain, loss mechanisms such as ice scatter and material absorption may be included 'exactly' rather than perturbatively. In addition, leaky modes may be computed. The price of this non-perturbative treatment is a slowdown in speed by approximately a factor of 4. This factor principally represents the difference between complex and real arithmetic.
A further slow down by a factor of 2 or more may occur it the Twersky scatter option is used in KRAKENC. The calculation of the Twersky scatter function can require significant CPU time; enough to actually be a dominant part of the cost of computing the modes. KRAKEN incorporates the scatter perturbatively and is much less sensitive to the cost of Twersky scatter.
KRAKEN does not at allow for losses in elastic media due to material attenuation. Thus, for attenuating elastic media, KRAKENC should be used.
Files:
Name Unit Description
Input
*.ENV 1 ENVironmental data
*.BRC 10 Bottom Refl. Coef. (optl)
*.TRC 11 Top Refl. Coef. (optl)
*.IRC 12 Internal Refl. Coef. (optl)
Output
*.PRT 6 PRinT file
*.MOD 20 MODe file
---------------------------------------------------------
EXAMPLE AND DESCRIPTION OF ENV FILE:
'FRAMIV Twersky S/S ice scatter' ! TITLE
50.0 ! FREQ (Hz)
4 ! NMEDIA
'NSF' ! OPTIONS
0.0092 8.2 5.1 ! BUMDEN (1/m) ETA (m) XI (m)
750 0.0 3750.0 ! NMESH SIGMA (m) Z(NSSP)
0.0 1436.0 0.0 1.03/ ! Z(m) CP CS(m/s) RHO(gm/cm3)
30.0 1437.4 /
50.0 1437.7 /
80.0 1439.5 /
100.0 1441.9 /
125.0 1444.6 /
150.0 1450.0 /
175.0 1456.1 /
200.0 1458.4 /
250.0 1460.0 /
300.0 1460.5 /
350.0 1460.6 /
400.0 1461.0 /
450.0 1461.5 /
500.0 1462.0 /
600.0 1462.9 /
700.0 1463.9 /
800.0 1464.8 /
900.0 1465.8 /
1000.0 1466.7 /
1100.0 1467.0 /
1200.0 1469.0 /
1300.0 1469.5 /
1400.0 1471.8 /
1600.0 1474.5 /
1800.0 1477.0 /
2000.0 1479.6 /
2500.0 1487.9 /
3750.0 1510.4 /
35 0.0 3808.33
3750.0 1504.6 0.0 1.50 .15 0.0
3808.33 1603.07 /
35 0.0 3866.66
3808.33 1603.07 0.0 1.533 .15 0.0
3866.66 1701.53 /
35 0.0 3925.0
3866.66 1701.53 0.0 1.566 .15 0.0
3925.0 1800.0 /
'A' 0.0 ! BOTOPT SIGMA (m)
3925.0 1800.0 0.0 1.60 .15 0.0
0.0 1504.0 ! CLOW CHIGH (m/s)
300.0 ! RMAX (km)
1 100.0 / ! NSD SD(1:NSD) (m)
1 200.0 / ! NRD RD(1:NRD) (m)
---------------------------------------------------------------
DESCRIPTION OF INPUTS:
(1) - TITLE
Syntax:
TITLE
Description:
TITLE: Title of run enclosed in sinqle quotes.
(2) - FREQUENCY
Syntax:
FREQ
Description:
FREQ: Frequency in Hz.
(3) - NUMBER OF MEDIA
Syntax:
NMEDIA (<20)
Description:
NMEDIA: Number of media.
The problem is divided into media within which it is
assumed that the material properties vary smoothly. A new
medium should be used at fluid/elastic interfaces or at
interfaces where the density changes discontinuously. The
number of media in the problem is defined excluding the
upper and lower half-space.
(4) - OPTIONS
Syntax:
OPTION
Description:
OPT(1:1): Type of interpolation to be used for the SSP.
'C' for C-linear,
'N' for N2-linear (n the index of refraction),
'S' for cubic Spline,
'A' for Analytic. The user must modify the
analytic formulas in PROFIL.FOR then
compile and link.
If your not sure which option to take, I'd suggest
you use 'C' or 'N'. Practically, you can pick
either one: the choice has been implemented to
facilitate precise intermodel comparisons.
Option 'S' is a little dangerous because splines
yield a poor fit to certain kinds of curves,
e.g. curves with sharp bends. If you insist
on splines, you can fix a bad fit by dividing the
water column into two 'media' at the bend.
Run PLOTSSP to check that the SSP looks the way you
thought it should. Apart from potential typos,
this will also show up fit-problems.
OPT(2:2): Type of top boundary condition.
'V' VACUUM above top.
'A' ACOUSTO-ELASTIC half-space.
Requires another line as described in
block (4a).
'R' Perfectly RIGID.
'F' Reflection coefficient from a FILE
(available in KRAKENC only). Requires
additional lines as described in
block (4c).
'S' for Soft-boss Twersky scatter.
'H' for Hard-boss Twersky scatter.
'T' for Soft-boss Twersky scatter, amplitude
only.
'I' for Hard-boss Twersky scatter, amplitude
only. The Twersky scatter options require
another line as described in block
(4c). Mnemonically, T, I options are one
letter after S, H in the alphabet. Current
wisdom is that option T is most
appropriate for ice scatter.
For open ocean problems option 'V' should be
used for the top BC. The Twersky options
are intended for under-ice modeling.
OPT(3:3): Attenuation units.
'N' Nepers/m.
'F' dB/(kmHz) (F as in Freq. dependent)
'M' dB/m (M as in per Meter)
'W' dB/wavelength (W as in per Wavelength)
'Q' quality factor.
'T' Thorp attenuation formula. This overrides
any other attenuations specified.
KRAKEN ignores material attenuation
in elastic media. (KRAKENC treats
it properly).
OPT(4:4): Slow/robust root-finder.
'.' As in: I want all the modes and I don't
care how long it takes. Period.
(Available in KRAKENC only.)
In certain problems with elastic layers
the old root-finder has been known to
skip modes.
(4a) - TOP HALFSPACE PROPERTIES
Syntax:
ZT CPT CST RHOT APT AST
Description:
ZT: Depth (m).
CPT: Top P-wave speed (m/s).
CST: Top S-wave speed (m/s).
RHOT: Top density (g/cm3).
APT: Top P-wave attenuation. (units as given in Block 2)
AST: Top S-wave attenuation. ( " " " " " ")
This line should only be included if OPT(2:2)='A', i.e.
if the user has specified a homogeneous halfspace for
the top BC.
(4b) - TOP REFLECTION COEFFICIENT
Syntax:
NTHETA
THETA(1) RMAG(1) RPHASE(1)
THETA(2) RMAG(2) RPHASE(2)
.
.
.
THETA(NTHETA) RMAG(NTHETA) RPHASE(NTHETA)
Description:
NTHETA: Number of angles.
THETA(): Angle.
RMAG(): Magnitude of reflection coefficient.
RPHASE(): Phase of reflection coefficient (degrees).
Example:
3
0.0 1.00 180.0
45.0 0.95 175.0
90.0 0.90 170.0
These lines should be contained in a separate '.TRC' file.
This file is only required if OPT(2:2)='F', i.e. if the
user has specified that the top BC is read from a '.TRC'
(Top Reflection Coefficient) file.
This option for tabulated reflection coefficients is
somewhat experimental at this time. I haven't worried about
the multivalued character of the phase function: choose
your reference and make sure the phase varies continuously.
A complicated reflection coefficient may well cause
problems for the mode-finder.
(4c) - TWERSKY SCATTER PARAMETERS
Syntax:
BUMDEN ETA XI
Description:
BUMDEN: Bump density (ridges/km).
ETA: Principal radius 1 (m).
XI: Principal radius 2 (m).
This line should only be included when one of the
Twersky-scatter options is selected.
(5) - MEDIUM INFO
Syntax:
NMESH SIGMA Z(NSSP)
Description:
NMESH: Number of mesh points to use initially.
The number of mesh points should be about 10
per vertical wavelength in acoustic media. In
elastic media, the number needed can vary quite
a bit; 20 per wavelength is a reasonable
starting point.
The maximum allowable number of mesh points is
given by 'MAXN' in the dimension statements.
At present 'MAXN' is 50000. The number of mesh
points used depends on the initial mesh and the
number of times it is refined (doubled). The
number of mesh doublings can vary from 1 to 5
depending on the parameter RMAX described
below.
If you type 0 for the number of mesh points,
the code will calculated NMESH automatically.
SIGMA: RMS roughness at the interface.
Z(NSSP): Depth at bottom of medium (m).
This value is used to detect the last SSP point
when reading in the profile that follows.
(5a) - SOUND SPEED PROFILE
Syntax:
Z(1) CP(1) CS(1) RHO(1) AP(1) AS(1)
Z(2) CP(2) CS(2) RHO(2) AP(2) AS(2)
.
.
.
Z(NSSP) CP(NSSP) CS(NSSP) RHO(NSSP) AP(NSSP) AS(NSSP)
Description:
Z(): Depth (m).
The surface starts at the first depth point
specified. Thus if you have say, XBT data which
starts at 50 m below the surface, then you'll
need to put in some SSP point at 0 m, otherwise
the free-surface would be placed at 50 m giving
erroneous results. The points Z(1) and Z(NSSP)
MUST correspond to the depths of interfaces
between media.
CP(): P-wave speed (m/s).
CS(): S-wave speed (m/s).
RHO(): Density (g/cm3).
Density variations within an acoustic medium
are at present ignored.
AP(): P-wave attenuation (units as given in Block 2)
AS(): S-wave attenuation ( " " " " " ")
These lines should be omitted when the 'A' option is used
(indicating that an analytic profile is supplied by a user
written subroutine).
The '/' character signals that the remaining data on the
line is the same as in the previous line of SSP data. For
the very first line the default or 'previous' line is:
0.0 1500.0 0.0 1.0 0.0 0.0
This block should be repeated for each subsequent medium.
(6) - BOTTOM BOUNDARY CONDITION
Syntax:
BOTOPT SIGMA
Description:
BOTOPT: Type of bottom boundary condition.
'V' VACUUM below bottom.
'A' ACOUSTO-ELASTIC half-space.
Requires another line with the half-space
parameters. The format is the same as that
used for specifying the top halfspace BC.
'R' Perfectly RIGID.
'F' reflection coefficient from a FILE (available
in KRAKENC only). Requires a Bottom
Reflection Coefficient file with
extension '.BRC'. The format is the same as
that used for a Top Reflection coefficient.
'P' Precaculated internal reflection coefficient
from a FILE (available in KRAKENC only).
These files are generated using BOUNCE.
Option 'A' is generally used for ocean bottom
modeling.
SIGMA: Interfacial roughness (m).
(7) - PHASE SPEED LIMITS
Syntax:
CLOW CHIGH
Description:
CLOW: Lower phase speed limit (m/s).
CLOW will be computed automatically if you set
it to zero. However, by using a nonzero CLOW you
can skip the computation of slower modes. Mainly
this is used to exclude interfacial modes (e.g.
a Scholte wave). The root finder is especially
slow in converging to these interfacial
modes and when the source and receiver are
sufficiently are far from the interface the
interfacial modes are negligible.
CHIGH: Upper phase speed limit (m/s).
The larger CHIGH is, the more modes are
calculated and the longer the execution time.
Therefore CHIGH should be set as small as
possible to minimize execution time.
On the other hand, CHIGH controls the maximum
ray angle included in a subsequent field
calculation-- ray paths are included which turn
at the depth corresponding to CHIGH in the SSP.
Thus a larger CHIGH means more deeply
penetrating rays are included.
Choice of CHIGH then becomes a matter of
experience. In the far-field and at
high-frequencies, rays travelling in the ocean
bottom are severely attenuated and one may set
CHIGH to the sound speed at the ocean bottom. In
the near-field, low-frequency case, rays
refracted in the bottom may contribute
significantly to the field and CHIGH should be
chosen to include such ray paths.
KRAKEN will (if necessary) reduce CHIGH so that
only trapped (non-leaky) modes are computed.
KRAKENC will attempt to compute leaky modes if
CHIGH exceeds the phase velocity of either the
S-wave or P-wave speed in the half-space. Leaky
mode computations are somewhat experimental at
this time.
(8) - MAXIMUM RANGE
Syntax:
RMAX
Description:
RMAX: Maximum range (km).
This parameter should be set to the largest
range for which a field calculation will be
desired.
During the mode calculation the mesh is doubled
successively until the eigenvalues are
sufficiently accurate at this range. If you set
it to zero, then no mesh doublings will be
performed. You don't need to worry too much
about this parameter-- even if you set it to
zero the results will usually be reasonable.
(9) - SOURCE/RECEIVER DEPTH INFO
Syntax:
NSD SD(1:NSD)
NRD RD(1:NRD)
Description:
NSD: The number of source depths.
SD(): The source depths (m).
NRD: The number of receiver depths.
RD(): The receiver depths (m).
This data is read in using list-directed I/O so you can
type it just about any way you want, e.g. on one line or
split onto several lines. Also if your depths are
equally spaced then you can type just the first and last
depths followed by a '/' and the intermediate depths
will be generated automatically.
CPU time is essentially independent of the number of
sources and receivers so that you can freely ask for up
to 4095 depths. However, for high-frequencies the
storage for the mode files can be excessive.
The source/rcvr depths are sorted and merged and then the
modes are calculated at the union of the two sets
of depths. Thus, it doesn't matter if you mix up source
and receiver depths. Furthermore, you can leave out
either the source or receiver specification (but not
both simultaneously) simply by using a '/' for that
line.
Sources and receivers cannot be placed in a half-space.
If you are going to be doing a coupled-mode calculation
then you must specify a large number of receiver depths
spanning the entire column (down to the half-space).
Fine sampling (about 10 points/wavelenght) is needed
to calculate the coupling integrals accurately.
--------------------------------------------------------------
SAMPLE PRINT OUT
The print-out for this deck is shown below
KRAKEN- FRAMIV Twersky S/S ice scatter
Frequency = 20.00 NMEDIA = 4
N2-LINEAR approximation to SSP
Attenuation units: dB/mkHz
TWERSKY SOFT BOSS surface scatter model
Twersky ice model parameters:
Bumden = 0.920000E-02 Eta = 8.20 Xi = 5.10
Z ALPHAR BETAR RHO ALPHAI BETAI
( Number of pts = 750 RMS roughness = 0.000E+00 )
0.00 1436.00 0.00 1.03 0.0000 0.0000
30.00 1437.40 0.00 1.03 0.0000 0.0000
50.00 1437.70 0.00 1.03 0.0000 0.0000
80.00 1439.50 0.00 1.03 0.0000 0.0000
100.00 1441.90 0.00 1.03 0.0000 0.0000
125.00 1444.60 0.00 1.03 0.0000 0.0000
150.00 1450.00 0.00 1.03 0.0000 0.0000
175.00 1456.10 0.00 1.03 0.0000 0.0000
200.00 1458.40 0.00 1.03 0.0000 0.0000
250.00 1460.00 0.00 1.03 0.0000 0.0000
300.00 1460.50 0.00 1.03 0.0000 0.0000
350.00 1460.60 0.00 1.03 0.0000 0.0000
400.00 1461.00 0.00 1.03 0.0000 0.0000
450.00 1461.50 0.00 1.03 0.0000 0.0000
500.00 1462.00 0.00 1.03 0.0000 0.0000
600.00 1462.90 0.00 1.03 0.0000 0.0000
700.00 1463.90 0.00 1.03 0.0000 0.0000
800.00 1464.80 0.00 1.03 0.0000 0.0000
900.00 1465.80 0.00 1.03 0.0000 0.0000
1000.00 1466.70 0.00 1.03 0.0000 0.0000
1100.00 1467.00 0.00 1.03 0.0000 0.0000
1200.00 1469.00 0.00 1.03 0.0000 0.0000
1300.00 1469.50 0.00 1.03 0.0000 0.0000
1400.00 1471.80 0.00 1.03 0.0000 0.0000
1600.00 1474.50 0.00 1.03 0.0000 0.0000
1800.00 1477.00 0.00 1.03 0.0000 0.0000
2000.00 1479.60 0.00 1.03 0.0000 0.0000
2500.00 1487.90 0.00 1.03 0.0000 0.0000
3750.00 1510.40 0.00 1.03 0.0000 0.0000
( Number of pts = 35 RMS roughness = 0.000E+00 )
3750.00 1504.60 0.00 1.50 0.1500 0.0000
3808.33 1603.07 0.00 1.50 0.1500 0.0000
( Number of pts = 35 RMS roughness = 0.000E+00 )
3808.33 1603.07 0.00 1.53 0.1500 0.0000
3866.66 1701.53 0.00 1.53 0.1500 0.0000
( Number of pts = 35 RMS roughness = 0.000E+00 )
3866.66 1701.53 0.00 1.57 0.1500 0.0000
3925.00 1800.00 0.00 1.57 0.1500 0.0000
ACOUSTO-ELASTIC half-space, ( RMS roughness = 0.000E+00 )
3925.00 1800.00 0.00 1.60 0.1500 0.0000
CLOW = 0.00000E+00 CHIGH = 1504.0
RMAX = 300.0000000000000
Number of sources = 1
100.0000
Number of receivers = 1
200.0000
Mesh multiplier CPU seconds
1 16.4
2 15.1
I K ALPHA PHASE SPEED
1 0.8625082052E-01 -0.8519020992E-06 1456.956646
2 0.8582849772E-01 -0.1302695655E-06 1464.125663
3 0.8562855085E-01 -0.1059327457E-06 1467.544468
4 0.8545402623E-01 -0.1136748056E-06 1470.541667
5 0.8527187871E-01 -0.1192384459E-06 1473.682861
6 0.8510445198E-01 -0.1156165482E-06 1476.582050
7 0.8495255965E-01 -0.1130917467E-06 1479.222129
8 0.8479984039E-01 -0.1185453302E-06 1481.886116
9 0.8465149335E-01 -0.1314814525E-06 1484.483039
10 0.8450452348E-01 -0.1255743704E-06 1487.064845
11 0.8435857532E-01 -0.1276318031E-06 1489.637606
12 0.8421637950E-01 -0.1377681231E-06 1492.152796
13 0.8407780307E-01 -0.1377169389E-06 1494.612151
14 0.8393959060E-01 -0.1339925824E-06 1497.073136
15 0.8380370528E-01 -0.1378254389E-06 1499.500598
16 0.8367091002E-01 -0.1450063419E-06 1501.880476
--------------------------------------------------------------
If the program aborts in some way, examine the print file which is produced. Frequently an expected line has been omitted and the environmental file is therefore misinterpreted.
The message "FAILURE TO CONVERGE IN SECANT" occurs when KRAKEN requires more than 500 iterations to converge to a mode. Usually less than 20 iterations are needed but convergence to interfacial modes (Scholte or Stoneley waves) can be exceptionally slow, especially at higher frequencies. The simplest solution is to exclude interfacial modes by setting the lower phase-speed limit to the minimum p-wave speed in the problem. Alternately, you can increase the value of MAXNIT which controls the MAXimum Number of ITerations in the root finder.