„3. 
in this country in research and discover, work of natural 
recources, in ground investigation for road and highway 
planning, in the protection of cultural and architectural 
monuments, in environment protection and national economy 
planning. 
The acquiring of initial data for photogrammetric work 
in the People's Republic of Bulgaria is performed by object 
photography from airborne vehicles of ground stations. 
Air photography for cartographic purposes is carried 
out from planes of the type An-14, IL-14, An-50 etc. 
The planes are equipped with various cartographic aerocameras 
such as RCB, RC10, produced by the firm Wild (Switzerland), 
MRB21, MRB 11,5, MRB15 Zeiss Jena (GDR), RMK21, RMK15, - 
Zeiss OPTON (GFR) and AFA41/7,5, AFA41/20, made in the USSR. 
Aerofilms with high sensitivity and decisive ability 
are used in air photography. The aerofilms Izopanchrom 15- 
800H with sensitiveness 700, made in the USSR and Aviphot- 
PAN 33 with sensitiveness 21 Din made in the GFR and Belgium 
are mainly used in our photos. 
There sas started in 1975 an aerial photography utilising 
the spectrozonal and multispectral photos for an expedient 
research work of geological and geophysical resources in 
this country. The multizonal aerophotographic apparatus con- 
sists of five aerocameras. Every aerocamera takes aerofilm 
sensitive to the different zone of the specter. The spectral 
sensitivity of these aerofilms varies within the limits of 
0,48 mc to 0,58 mc. 
A multispectral system for optical scanning is used 
also in getting information of a given district. The district