* SPARC*
(SACLANTCEN Pulse Acoustic Research Code) is an experimental
time-marched FFP. It treats problems with broadband or transient
sources, that is, pulses. The environmental file is patterned after
that used for * KRAKEN*
and * SCOOTER*
. The mathematical basis and
numerical algorithm is described in:

Michael B. Porter, ``The Time-Marched FFP for Modeling Acoustic Pulse Propagation,'' J. Acoust. Soc. Amer. 87, 2013--2023 (1990).

Files: Name Unit Description Input *.ENV 1 ENVironmental data *.STS 10 Source Time Series Output *.PRT 6 PRinT file *.GRN 20 GReen's function *.RTS 35 Receiver Time Series --------------------------------------------------------- EXAMPLE AND DESCRIPTION OF ENV FILE: 'Munk profile' 5.0 2 'NVWS' 500 0.0 5000.0 0.0 1548.52 0.0 1.0 0.0 0.0 200.0 1530.29 / 250.0 1526.69 / 400.0 1517.78 / 600.0 1509.49 / 800.0 1504.30 / 1000.0 1501.38 / 1200.0 1500.14 / 1400.0 1500.12 / 1600.0 1501.02 / 1800.0 1502.57 / 2000.0 1504.62 / 2200.0 1507.02 / 2400.0 1509.69 / 2600.0 1512.55 / 2800.0 1515.56 / 3000.0 1518.67 / 3200.0 1521.85 / 3400.0 1525.10 / 3600.0 1528.38 / 3800.0 1531.70 / 4000.0 1535.04 / 4200.0 1538.39 / 4400.0 1541.76 / 4600.0 1545.14 / 4800.0 1548.52 / 5000.0 1551.91 / 500 0.0 10000.0 5000.0 1551.91 0.0 1.00 1.0 0.0 10000.0 / 'R' 0.0 1500.0 1550.0 10.0 ! RMAX (km) 1 250.0 / ! NSD SD(1:NSD) (m) 26 0.0 5000.0 / ! NRD RD(1:NRD) (m) 'PH' 0.0 15.0 ! PULSE FMIN FMAX (Hz) 1 60.0 0.200 / ! NRR RR(1:NRR) (km) 6 1.0 3.0 5.0 10.0 20.0 30.0 ! NTOUT TOUT(1:NTOUT) -0.1 0.9 0.0 0.0 0.0 ! TSTART (s) TMULT ALPHA BETA V (m/s) The input structure is identical to KRAKEN except for additional option in line 4 and 4 additional lines at the end. OPT(4:4): Type of calculation 'S' for Snapshot. FIELDS must be run afterwards to convert the '.GRN' file to a '.SHD' file containing the pressure field. The shade file can then be plotted using PLOTFIELD. 'R' for Range stack (horizontal array). The time series is written in a '.RTS' (Receiver Time Series) file which can be plotted using PLOTTS 'D' for Depth stack (vertical array). The resulting time series can also be plotted using PLOTTS. Additional lines: (1) - SOURCE PULSE INFORMATION: Syntax: PULSE FMIN FMAX Description: PULSE(1:1): Type of interpolation to be used for the SSP 'P' Pseudo-Gaussian 'R' Ricker wavelet 'A' Approximate Ricker wavelet 'S' Single sine 'H' Hanning weighted four sine 'N' N-wave 'G' Gaussian 'F' From a '.STS' (Source Time Series) file. 'B' From a '.STS' file Backwards PULSE(2:2): Hilbert transforming. 'H' perform a Hilbert transform of the source 'N' don't Hilbert transforming is used to eliminate the left travelling wave. PULSE(3:3): Source sign flipping. '+' don't flip it (recommended) '-' flip it PULSE(4:4): Source filtering. 'L' low cut filter 'H' high cut filter 'B' both high and low cut filter 'N' no cut FMIN: Low cut frequency (Hz) FMAX: High cut frequency (Hz). This should be no higher than necessary since the CPU costs are proportional to the bandwidth. (3) - RECEIVER RANGES Syntax: NRR RR(1:NRR) Description: NRR: Number of receiver ranges RR(): Receiver ranges (km) This line is ignored unless option 'R' has been selected for a range-stack. (3) - OUTPUT TIMES Syntax: NTOUT TOUT(1:NTOUT) Description: NTOUT: Number of output times TOUT(): Output times (s) (3) - TIME INTEGRATION PARAMETERS Syntax: TSTART TMULT ALPHA BETA V Description: TSTART: Starting time for the march. This should always be earlier than the time at which the source begins to rise. TMULT: Time step multiplier. Specifying TMULT = 1.0 means that the maximum stable time step is used. ALPHA: Lumping parameter BETA: Explicitness parameter V: Convection velocity

A good check of convergence can be done by running an isovelocity problem with a gaussian pulse. The pulse should, of course, be undistorted at the receivers. Remember that Hilbert transforming the source causes it to rise early so TSTART has to be adjusted accordingly.

It's a good habit to plot the source function using PLOTTS before running SPARC. This is done by providing the same source information to PLOTTS that is used to drive SPARC. Thus, if you are using a pseudo-gaussian pulse in SPARC you specify a pseudo-gaussian in PLOTTS and look at the time series.

Tue Oct 28 13:27:38 PST 1997