Bachman Database

Richard Bachman produced a seabed geologic model that is a gridded database
containing water depth, sediment grain size, sediment thickness, and acoustic
basement type. Grid cells are squares of side length equal to 2 arc seconds.

The gridded database covers the area:

	32 degrees 45 minutes
117 degrees 26 minutes		117 degrees 14 minutes
	32 degrees 33 minutes

Geographic data files are provided for:

	surface sediment grainsize	(grainsiz.xyz)
	sediment thickness	(sedthkms.xyz)
	basement rock type	(basement.xyz)
	water depth	(depth.xyz)

(also needed is a sound speed profile, some are provided in the examples)

Each data file has a companion README file explaining the units, derivation,
and codes for land or null values (if any).

The geographic data files ( *.xyz ) contain (X,Y,Z) triples, where X is the
seconds west of 117 degrees 13 minutes west, and Y is seconds north of 32
degrees 32 minutes north. For example, if {x,y} = {-456,362}, the point is
456 seconds west of 117 degrees 13 minutes and 362 seconds north of 32 degrees
32 minutes.

The examples use a script call 'extract2.scr' that will take in a list of
lat-long positions, will convert the positions into the coresponding arc second
location in the database, and extract out the data corresponding to the lat-long
position.

There are three examples of extracting data from the bachman data base.
All three examples call the script 'extract2.scr' to do the extraction.
( note: matlab mapping toolbox required for range calculation )

Example 1:

The first example extracts the geo-acoustic data for the VLA location
during SWellEx-96. The script to run this example is getVLA_GeoModel.scr

VLA location: 32 40.254 117 21.620

run through extract2.scr produces:

column	1	2	3	4	5
	0.00	219.73	24.39	5.05	1.0

where:

	Column 1: Range (m) from initial point
	Column 2: Water Depth (m)
	Column 3: Two-way travel time in msec for sediment
	Column 4: Sediment Grain size
	Column 5: Basement Type (0-unknown, 1-Tertiary, 2-Cretaceous, 10-Land)

Example 2:

The second example extracts a cut line along the longitude line 117 degrees
20 minutes (for NS track). This is a range independent track line. The script
to run this example is plotBathyNS.scr.

Example 3:

The third example extracts a cut line along the lattitude line 32 degrees
39 minutes (for EW track). This is a range dependent track line. The script
to run this example is plotBathyWE.scr.

Bach2geo_MPL

Each of the above examples demonstrates how to extract data out of the Bachman geographic
data base. But it does not produce a geoacoustic model. The document 'geo_modl.doc'
explains how to construct a geoacoustic model from the output of the database.

The program bach2geo_MPL implements the steps documented in 'geo_modl.doc'. There
are two examples of how to use bach2geo_MPL.

Kraken Example

Using the results from Example 1, bach2geo_MPL is run to generate a kraken input.
Kraken is then run 13 times ( for 13 frequencies ), with a MFP range-depth ambiguity
surface computed from the average result of the 13 range-depth ambiguity surfaces.

RAM example

Using the results from Example 2, bach2geo_MPL is run to generate a RAM input file.
The RAM input file is then used to produce a Transmission Loss plot at 201 Hz.

Note that the computations to produce the geoacoustic model are dependent on the sound
speed profile used as well as the results from the Bachman data base.

Download the Bachman database here: bachmanDB.tar.gz (2 MB)

Download the bach2geo program and examples of how to run it
here: bach2geo.tar.gz (78 MB)

Note this software is compiled for Red Hat Linux, but the
source code is also present.

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