The Santa Barbara Channel Experiment (SBCX)

SBCX Tide Information

Matched Field Processing requires extensive knowledge of the ocean environment.  One of these items is waveguide height, or the distance between the surface of the water and the ocean floor.  The bathymetric data supplied on the bathymetry page gives distances at mean low tide.  It is important to correlate the signals played in the water with the relative position in the tide cycle, to obtain the correct waveguide height.

Unfortunately, during the experiment, no one bothered to monitor tide information directly at the array site.  The only recourse is to use tide prediction algorithms to estimate what the tides were during the experiment.   I would suggest using the software package xtide, available freely on the net.  It is a UNIX program which generates both text and graphical tide predictions.  This program uses a published algorithm provided by the National Ocean Service (a division of NOAA), which incorporates field data measured at NOAA monitoring stations.

The next problem is the distance between the closest monitoring stations and the FFP array site.  Consider the following map:

Each grid represents 15.625 kilometers.  The closest NOAA tide survey location is Rincon Island, which is approximately 28.25 kilometers from the FFP array.  Santa Barbara is approximately 45.25 km away, and Santa Monica 78.5 km away.  Tides for the three locations vary accordingly.  For example, consider the tides predicted during the FFP array survey expedition, which took place on April 15, 1998:
 
 

For this interval, tide cycles flowed from east to west.  One could eyeball the actual high and low tides at the FFP array were approximately 5 minutes ahead of the predictions for Rincon Island.  For the A/X 2 HDS, (which took place between 21:10 and 23:10 on April 11, 1998), the low tide (at 0.26 meters above mean low tide) occurred at 23:11 UTC at Rincon Island.  Specific tide levels in five-minute intervals for the duration of the HDS are given here.  The first column is the UNIX "C" time (seconds since 1970) and the second column is the meter offset from mean low tide.  The output was generated with the command:

tide -l "Rincon" -z -u m -b "1998-04-11 21:10" -e "1998-04-11 23:10" -m r -s "00:05"

This shows the depth of the water column during the A/X 2 HDS varied between 0.5 and 0.25 meters more than the derived bathymetric data for the area.

Last updated: 991004 Comments/Questions: pmd@alum.mit.edu

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