(4) 
the 141st meridian (the Alaska-Yukon boundary) and from Seven Islands, 
Quebec, northerly to Ungava Bay, this latter net lying some 2,500 miles east of 
the former. The northern areas, east of the Rocky Mountains, thus lack precise 
control in the form of either triangulation or levelling, and in this great area, 
astronomic positions have provided what control we have. With the introduction 
of electronic methods of distance measurement in recent years, the use of astro 
nomic positions for mapping control will decrease. Economic development has 
demanded better maps, and since time is a factor, electronic methods of estab 
lishing control furnish the answer in both speed and accuracy. 
Basic Operations 
The operations involved in a shoran-geodetic survey are not only extensive 
but complicated, and require the knowledge and co-operation of many organiza 
tions. A reconnaissance is made by air and then by ground to select antenna sites 
of sufficient height to provide straight-line clearance of ray paths to the plane 
engaged on line-measurement. For ease in transport these sites should be close 
to fairly large, deep lakes, with good landing beaches, thus reducing the lengths 
of trails and providing safety for the supply planes. Each site is permanently 
marked by a monument or tablet, and in wooded areas is cleared to form a 100' 
square. In the more northern interior regions basic elevations are non-existent. 
It is thus necessary to establish the elevation of Jake surfaces by barometric means 
over a period of 14 days, readings of wet-and-dry bulbs and barometer being 
taken every three hours at specified times to allow correlation of the data with 
the weather maps of the Meteorological Service. The elevation of the antenna 
site is obtained by spirit levelling from the lake surface. Radar altimetry would 
be of great assistance to this end and it would also provide numerous spot eleva 
tions, but at present it is not in use. An exploratory astronomic fixation is made 
at each site. From this, the navigator on line-crossing measurements is provided 
with information as to the approximate length and direction of each radiating 
line; azimuth is also calculated and marked on the ground for the antenna orienta 
tion. Subsequent comparison of exploratory with shoran values of fixation gives 
an approximate indication of the deflection of the vertical existing at each station. 
To perform these operations an extensive organization is required and the 
work has been done as a co-operative venture by personnel of the Royal Canadian 
Air Force, National Research Council, Meteorological Service and the Geodetic 
Survey of Canada. When it is realized that the field season is only about three 
months due to lakes not being open more than four months in the lower latitudes 
and progressively less as one approaches higher latitudes, one gains an apprecia 
tion of the necessity of personnel being highly trained in order to take full 
advantage of the short period of operation. The transportation of equipment and 
some 160 personnel 2,500 miles by air, the provision of food and shelter for them, 
the maintenance and operation of the antenna stations, and the servicing and 
operation of both line-measuring and supporting aircraft, coupled with the need 
for a high order of accuracy in the work, tend to make the operation a challenge 
to all concerned.