182 THE CANADIAN SURVEYOR May, 1960
of Shoran-controlled photography has been discontinued, chiefly because of the very
high cost involved in Shoran operations.
Use or Rapar PROFILE AS AUXILIARY DATA
Aerial triangulation based on radar profile data is probably the most advanced and
efficient method of aerial triangulation at present. The methods and equipment
developed in Canada since 1947 have undergone further refinements and improvements
during the period under review. The capsule-type altimeter has been replaced by an
altimeter which derives the differences in flying heights from the temperature differ-
ences of a boiling liquid exposed to atmospheric pressure at the flying altitude. This
new instrument allows operational radar profile flights up to 9000 m over sea level.
The sensitivity and the stability of the equipment was further increased, and the
profiles are now recorded at a vertical scale of about 1:1000 (one interval equals 5 ft)
which permits the profile points to be read with a precision of # 30 cm. Very detailed
investigations were carried out on profiles 20 km long over rolling terrain with 300 m
relative elevation differences, and Table I shows the accuracy for profile points within
flat areas.
TABLE I
Flying height | 3000 m | 6000 m
No. of points | 177 75
Mean square elevation
error mn 16m +1.7m
The accuracy of radar profiles, several hundred kilometers in length, encountered
in mapping operations, is naturally somewhat lower than the accuracy noted above.
However, when using the radar profile information is used as auxiliary data in aerial
triangulation, excellent results are obtained in elevations as well as in x-determination.
The bridging and adjustment procedure was refined during the reviewing period
and the National Research Council carried out successful experiments over mountainous
and hilly terrain, using flights up to 9000 m in altitude. The results of two typical
experiments over well-controlled areas are shown in Table Il.
TABLE II
: |
Length of | |
triangulated Flying | |
Type of terrain strip height | mz | Mx
|
Rugged mountains, elevation | |
differences about 1000 m 60 km 6000 m | +2.2m | +2.8 m
Rolling terrain, elevation |
differences about 600 m 200 km 9000 m | +2.5m | +—7.5m
In the official mapping program, large projects in particularly difficult areas are
based on radar profile data, and photographic flights with simultaneous radar profiles
were and are being carried out. The great advantage of this technique is that all the
necessary data are recorded in the aircraft simultaneously with aerial photography and
no contact with the ground is necessary. As a result the operational decisions rest
