[COMMISSION III Rs 
| Appendix 16 the INT. ARCHIVES OF 
| PHOTOSTAMNMUIEY, Yol. XIiba, 1956 
  
   
  
  
Airborne Control Method of Aerial Triangulation 
by T. J. BLACHUT, 
Photogrammetric Research, Division of Applied Physics, National Research 
Council of Canada, Ottawa. 
tion. 
Eus summation of various quantitatively unknown errors in a bridged strip, which 
„ade the law of propagation of errors, and the occurrence of sudden breaks caused by 
tumental or human failures, represent not only a very serious limitation to the 
bili of aerial triangulation but also undermine confidence in this method. 
This situation is especially noticeable in the mapping operations of vast, under- 
igeloped areas, where no net of ground control points exists or only a very sparse net. 
An attempt to include additional ground control points in order to make the use of the 
rial triangulation method reliable or at all possible would under certain circumstances 
uke the mapping operation impracticable because of the time and cost requirements. 
Introduction of electronic means opened new possibilities in this field. It became 
pssible to establish quickly a primary net of ground control points even in difficult terrain. 
The meshes in this net, however, seem to be too wide to be used directly for photogrammetric 
mpping. Using the same techniques the primary net can be densified, but electronic 
jerations require the setting of the field stations on all the points to be determined. Such 
qeations are by no means simple and unexpensive. 
(msequently a relatively simple and reliable method of aerial triangulation which would 
dw bridging of the longer distances would be the answer. The distances in question 
ue of the order of 300—400 km. A solution to this problem was made possible by the 
ivelopment of two new techniques which proved to by very useful in their photogrammetric 
gpiation. We are referring to the radar profile technique and to the use of infrared 
ilique photographs in order to determine a direction on the earth surface. This com- 
mnication will give a short description of the method developed and of the results obtained 
far À full account will be found in a later publication on this subject now being 
| nepared. 
ladar profile and infrared oblique photographs. 
From the very beginning of the investigation on the radar profile technique its import- 
ice was realized not only as a means to establish vertical control within a mapped area 
lit also as a means for carrying forward the scale. In consequence, the APR (Airborne 
Mile Recorder) equipment was modified to provide, in addition to the ground profile, 
àgraphical recording of ground clearances (distances between the aircraft and the ground 
face reflecting electromagnetic pulses). The radar profile of the terrain is the difference 
leen flying heights and ground clearances. Flying height is determined barometrically 
ad ground clearance is determined electronicly by measurement of the time for a pulse 
im the aireraft to reach the ground and return (Fig. 1). Therefore, if two of the three 
Wanities (eround profile, ground clearance and flying height) are recorded, the third 
île can be easily derived. 
lle accuracy of radar profile points depends, first of all, upon the type of terrain. In 
{at and rolling country where the elevation points can be selected within relatively flat 
af pen areas, the mean square error in elevation may vary from €t 2 m to 3 m 
Bending upon general conditions. 
Experimental work covered flying heights from 1500 metres to 6000 metres and very 
“factory results were obtained. At present experimental flights at 9000 m altitude are 
tng carried out, 
  
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