OF 03-150 Home
Sound Velocity Profiles
When acquiring bathymetric data, the time of travel of
an acoustic wave from the transducer to the seafloor and back (two-way
travel time) is measured; depth is not directly measured. In order to convert
travel time to depth, the speed of sound in the water column must be
measured (Fig. 8). The depth measurements, or soundings, will be limited
by the accurate measurement of the speed of sound profile in space and time.
Any changes in temperature (thermolcine), salinity (halocline), and/or
pressure (pycnocline) with depth will result in refraction (ray bending) of non-normal acoustic
ray paths (Fig. 9). In order to calculate a correct depth at the proper position
on the seafloor, the ray paths must be accurately modeled. Thus, if the velocity structure of the water column is not properly modeled, incorrect
depth measurements will be recorded due to inaccurate time-to-depth convsersions and inaccurate modeling of non-normal
8. Diagram showing two-way travel of an acousitc ray,
normal to the transdcuer.
|Figure 9. Diagram showing the two-way travel of a non-normal acoustic ray.
Eighteen sound velocity profiles were collected throughout
Bear Lake using an
Applied Microsystems SVP Plus sound velocimeter. The locations
of the profiles are displayed within Figure
4. Thumbnails of the sound veloicty profiles are listed below.
Click on a thumbnail to view a full resolution version of
the sound velocity profile. These data are also stored within
the ArcView project file and as an MS Excel spreadsheet in
the svp directory. See GIS Data
and CD Contents for more information.
|Figure 4. Map showing
location of grab samples and sound velocity profiles.
To view files in PDF format, download free copy of Adobe Acrobat Reader www.adobe.com/products/acrobat/alternate.html.