# FIELDS

#

The FIELDS program uses the Green's functions calculated by SCOOTER or SPARC and produces a shade file that contains a sequence of snapshots of the acoustic field as a function of range and depth.

Files:

Name Description

Input

*.FLP FieLd Parameters

*.GRN GReen's function

Output

*.PRT PRinT file

*.SHD SHaDe file

## EXAMPLE AND DESCRIPTION OF FLP FILE:

'RP' ! 'R/X (coord), Pos/Neg/Both'
1001 ! NRr number of receiver ranges
0.0 100.0 / ! Rr( 1 : Nrr ) receiver ranges (km)

(1) - OPTIONS

Syntax:

OPT

Description:

OPT(1:1): Coordinates

'R' Cylindrical (R-Z) coordinates using the far-field approximation to the Hankel functions.

'X' Cartesian (X-Z) coordinates.
'H' Hankel functions used to provide the exact transform (a bit slower but more accurate)
(only available in the Matlab fieldsco.m)

OPT(2:2): Spectrum

'P' Positive (recommended)

'N' Negative

'B' Both positive and negative

The spectral integral should formally be done from all along the real k-axis, however the negative portion contributes significantly only in the near-field. Run-time is less if it is neglected.

OPT(3:3): Interpolation type

'O' POlynomial (for broadband runs) (default)

'A' PAde (can produce better results for CW runs but is less reliable)

The Pade option (OPT(3:3)) is less robust. Use polynomial interpolation if an underflow/overflow occurs ...

OPT(4:4): Selects a source beam pattern

'*' Read in a source beam pattern file.

'O' Omnidirectional (default).

(3) - NUMBER OF RECEIVER RANGES

Syntax: NRr

Description:

NRr: Number of receiver ranges

In the Fortran field routine, the actual number of ranges used may be increased to satisfy FFT sampling requirements.

(3) - RECEIVER RANGES

Syntax: Rr( 1 : NRr )

Description:

Rr: Vector of receiver range (km)
If the vector is terminated with a '/', then a uniformly spaced vector of ranges is generated between Rr( 1 ) and Rr( 2 )