238 EXPLORATION GEOPHYSICS 



The measuring elements have been mounted in blisters on the wing 

 tips, in a special tail extension referred to as a stinger, or in a bomb-like 

 structure, called a bird, which is trailed beneath and behind the aircraft 

 at the end of a cable (Figure 117). In all cases the purpose is to get the 

 measuring element as far as possible from the disturbing magnetic masses 

 (chiefly engines) of the aircraft. No plane is available in which the full 

 inherent sensitivity of the instrument can be realized from an installation 



(Couitc'iy uf tiult Re-.carLh ami Development Co.) 

 Fig. 117. — Magnetometer bird, trailing airplane. 



in the plane itself, and in only very few types will the result be satisfactory 

 after elaborate means have been provided for compensating both the fixed 

 and variable magnetization of the aircraft structure. The navigation equip- 

 ment and the magnetometer electronic controls and amplifiers, together 

 with the recorder, are mounted in the passenger compartment (Figure 118). 

 The equipment is usually installed in line with the wings to give better 

 stability for operator comfort. 



A continuous record is obtained of the magnetic intensity along the 

 flight path of the airplane. To make this record usable, the position of the 

 plane, that is, vertical projection on ground and elevation above ground, 

 must be accurately known for each point on the magnetometer graph. 

 The elevation may be obtained by use of a radio altimeter and may be 

 continuously recorded on a photographic film. In some cases where contact 

 flying may be employed, the position is obtained by photographing the 

 ground beneath, using a slit camera in which the speed of a continuous 

 film is so synchronized that the image and film are instantaneously relatively 



