“Dw 
85 miles from the two passages. A full crew of nine was 
carried, and the writer went along as observer and 
technical advisor. The sorties extended over 8 hours on 
November 22, and 7 1/2 hours on April 15. 
Standard survey techniques were used, the camera 
being a Williamson F224 of 6" focal length and 9" x 9" 
negative format. It was mounted in the rear compartment 
and was switched on and off by intercom orders from the 
navigator in the nose position. Super XX Aero film was 
used for all photography, the developing and printing being 
done at the R.C.A.F. Central Photographic Establishment, 
at Rockcliffe base, Ottawa. 
The scale specified was l" - 1000! requirinc a 
flying height of 6000'. This scale was considered the best 
compromise between the necessity for covering the passages 
from side to side, and the desire for as large a scale as 
possible. However, due to cloud conditions, it was necessary 
to take over 50% of the photography from 3000! giving a 
scale of 1" - 500'. This lower altitude required much 
closer navigation in order to assure lateral coverage, but 
was entirely Successful, no strips being lost due to lack 
of side lap on the land area. Study of the photography 
and later experiments indicate that Still smaller scales 
could be used successfully. Continuous strip coverage from 
medium altitudes offers some interesting possibilities. 
The application of this technique to very large, or long 
wave length waves and currents is discussed in the section 
on continuing research. 
Flight Plan: 
The flight plan (Fig.2) was designed to bring the 
photo aircraft over each passage at fifteen minute intervals, 
Due to the time required to fly from Petit to Grand Passage 
in a left hand circuit it will be notsd that the strips are 
offset by five minutes relative to each other. The ground 
speed and photo time interval were carefully recorded. A 
graphic log of the sorties is given in Fig. 3. 
Results: 
Maps were prepared from the photos by plotting 
the maxima directly on Stereopairs under a mirror 
stereoscope and by form lining the (apparently) elevated 
or depressed surfaces. Velocities were neasured with a 
parallax bar, using a simple graph to eliminate computation. 
This could be done in a Precision plotter, if it were