The Santa Barbara Channel Experiment (SBCX)

Bathymetry

Bathymetric Databases

• Original SAIC-supplied (David Gever) bathymetric database, obtained from Dick Bachman at SPAWAR. This is a 5 MB text file with three columns of data: longitude, latitude, and depth of bottom at mean low tide. Data is arranged in a grid, from 33.75 to 34.5 degrees latitude north, and 118.75 and 120 degrees longitude west. The longitude grid spacing is between 0.003 and 0.004 degrees, while the latitude grid spacing is between 0.0016 and 0.0017 degrees. [sbcxbath.dos] gzip-compressed: [sbcxbath.dos.gz]
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• Above database, with entries converted from lat/long pairs to UTM (WGS-84). This is another large text file, with four columns of data: UTM X coordinate (in meters), UTM Y coordinate (again, in meters), the depth of the bottom at mean low tide (meters), and the UTM grid (11S for the entire SBCX dataset). The transformation from lat/long to UTM results in a bathymetric grid which is no longer orthogonal. [sbcxbath.utm] gzip-compressed: [sbcxbath.utm.gz]
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• Contour database. This is used as input to the plot_bathymetry program listed below. Due to the non-orthogonal grid spacing in the UTM bathymetric database, a special program had to be written to trace contours around the bathymetric points. [sbcxvect.utm] gzip-compressed: [sbcxvect.utm.gz]
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Bathymetric Programs

• Coordinate transformation routines: These C language functions convert lat/long coordinate pairs to/from UTM coordinate pairs. These functions use equations taken from John Snyders' Map Projections: A Working Manual, USGS Professional Paper 1395.
  • convert_datum.h
  • convert_datum.c
• Bathymetric extraction program: This program prints out the bathymetry between two points. The two points can be specified in either lat/long or UTM pairs, and the range step interval can be specified on the command line.
  • bath-util.h
  • bath-util.c
  • extract_bath.c
  This program needs the convert_datum.h and convert_datum.c files to compile correctly. The compilation line is as follows:

  gcc -o extract_bath extract_bath.c bath-util.c convert_datum.c -lm

• Mapping software: This program generates a contour plot, in UTM coordinates, of the SBCX test area. One can interactively select a magnification level, as well as center coordinates. The program accepts coordinate files (in either lat/long or UTM) which can specify lines to be overlaid on the map. This is useful for plotting ship or target tracks.
  • plot_bath.c
  This program needs the convert_datum.h and convert_datum.c files to compile correctly. The compilation line is as follows:

  gcc -o plot_bath plot_bath.o convert_datum.o -L/usr/X11R6/lib -lX11 -lm

  This program uses X windows to display the output. It also requires the UTM bathymetric grid file, sbcxbath.utm and the bathymetric contour file sbcxvect.utm to display.

  One can overlay ship tracks or other lines on the plot, by using a very simple text file. The format of the file is as follows:
  

  Line 1: LL (or) UTM

  Specify LL if the data to be plotted is furnished in lat/long pairs, or UTMif the data is in UTM coordinate pairs.

  Line 2: color

  Specify the color which the coordinate data should be plotted in

  Line 3: width

  Specify the line width (in number of pixels)which should be plotted

  Lines 4 through the end of file: latitude, longitude (or) UTM X, UTM Y

  If one specifies latitude/longitude pairs, they should be in decimal notation separated by commas, not HHMMSS. Characters on the line after the coordinate pairs are ignored.

  Here is an example overlay file, for the A/X 2 Hot Data Set

  
  

The user interface for the plotting program is very simple. There are three controls: the left, middle, and right mouse buttons. Pressing the left mouse button will zoom the contour plot in by a factor of two. Pressing the middle mouse button will zoom the countour plot out by a factor of two. Pressing the right mouse button will redraw the contour plot.

Contour depths are not labeled; however, black contour lines are drawn at 10 meter intervals. Red contour lines are drawn at 50 meter intervals, and dark green contour lines are drawn at 500 meter intervals. By passing the cursor over the contour line in question, one can obtain the depth for that contour line.

The FFP array is always drawn on the plot as a bright green pentagon outline.

Last updated: 991202 change log Comments/Questions: pmd@alum.mit.edu

Ships in the SBCX logo (left to right, from the top) Lockheed P-3 ("Redhook"), Acoustic Explorer, FLIP, Danny C, USS Dolphin.