A pair of oceanographic transects were obtained by JEHC on the 3rd of
August 2006 onboard the CCGS Frederick G. Creed. The data were obtained
using a BOT-MVP-100 outfitted with an AML Sv,T & Z probe. The MVP
was set to cycle automatically, achieving a depth of ~ 80m on average
at 12 knots with an inter-dip spacing of ~ 500m.
Outbound profile (Saint John Harbour to Gulf of Maine) - dips 005 - 173
Inbound profile (Gulf of Maine to Approaches to Digby Basin) dips 174 -
By inverting the Chen and Millero relationship, one can estimate the
salinity from the temperature, sound speed and depth of the sensor
output. Using the temperature, depth and derived salinity, the density
can in-turn be derived using the UNESCO formulae.
LABORATORY EXERCISE - GGE5013 - Autumn 2006
- Outward bound dips only (005-173)
- download the data
- plot up the locations (see if you can find a suitable
cartographic backdrop image)
- calculate the time and distance (and speed) between dips and make
a plot to see what penetration an MVP-100 can achieve as function of
speed and depth.
- plot the bottom depth along the profiles by distance (can be
found in each ascii file)
- plot up the temperature and sound speed profiles of the outward
bound profiles - show the 0-120m depth range
- using the T, Vp and Z, try to estimate the Salinity for
- draw a distance - profile of the near surface (1-3m) temperature,
salinity and sound speed along the transect.
- using the T, Z and derived Salinity, try to estimate the Density for
- plot up the salinity and density profiles of the outward
bound profile - show the 0-120m depth range
- make a display of the cross section profiles of Vp, T, S and density by distance
along the outward profile
- Calculate and plot a section of the Brunt Vaisala
(buoyancy) frequency profile for each dip.
8/20 for the above.....
To help you get going a skeleton C program is available here.
This should speed up the manipulation of the raw data to make useful
Significance to the Oceanographic
Explain the main oceanographic features visible in the profile.
Try to obvtain a SST image of the region. Go to :
Try to find cloud free images as close in time to the profile observed.
You may have to go forward or back a few days.
- Try to plot the profile across the image (can you register the
- Can you see any resemblence between the SST image and the surface
temperature plot that you made .
- Can you see any differences?
- How variable is the SST inthat area from image to image and from
day to day ?
- Would the profile have been similar if the section had been made
further to the north or south?
Consequences for Hydrographic Survey
Controls on Sound Speed
Compare and contrast the relative importance of temperature versus
salinity in influencing the sound speed cross-section.
Estimating the Sensitivity of
the refracted ray path to water column structure:
Pick 5 end-member Vp profiles that are representative of the main
Pick one and do a ray trace for a beam (starting at a depth of
with the following launch angles of 0, 30 50 65 & 70 degrees until
you reach a depth of 75m.
Extract the TWTT to reach that depth for that profile for each of the
angles (and record the across-track distance achieved).
For each of the other 4 profiles, using the same TWTT, see what depth
and across-track distance you would achieve.
- What is the range of depth and across-track errors ?
- What does this mean in terms of IHO acceptance ?
Ascii Listing of Geographic Coordinates of each dip HERE
gzipped tarfile of each MVP dip for outbound
gzipped tarfile of each MVP dip inbound
generated by JEHC on September 25th 2006