Water Current Measurement by Tidal Cycle Photography
by
H. L. Cameron
Director, Photogrammetry and Geology Division
Nova Scotia Research Foundation
Introduction:
The strong tidal currents in Petit Passage and
Grand Passage, two narrow straits in western Nova Scotia
near the entrance to the Bay of Fundy make pier and other
harbour construction difficult to plan and maintain (Fig. 1)
As an aid to engineering planning the two straits
were photographed every fifteen minutes throughout a
complete tidal cycle. That is, from low to high tide and
from high to low tide, 86 strips in all being taken. This
required two sorties which were separated by six months in
time, because of the exigencies of weather and availability
of aircraft. The photography was carried out by 408 Squadron
R.C.A.F. Rockcliffe, at the request of the Dominion Public
Works Department of Canada.
The methedyof water current measurement by
anomalous parallax was used to plot the position and
velocities of current maxima. Forty six maps of Petit
Passage have been prepared, and, when taken in groups on a
light table, show the swing of the current at various times
during the tidal cycle. Counter currents and eddies were
mapped and their life spans and positions provide much
interesting and useful data for both engineers and
fishermen. The main value of this technique lies in the
synoptic picture of the currents and eddies, which it
provides.
Equipment and Techniques:
408 Squadron R.C.A.F. Rockcliffe Base carried
out the photography on November 23, 1958 and April 13, 1959,
A Lancaster bomber, modified for long range photography,
was used from R.C.A.F. Greenwood Base, which is located
(1) Cameron, H. L., 1952 "The Measurement of Water Current
Velocities by Parallax llethods™, Photogrammetric
Engineering, (arch 1952, pp 99-104