5.6 For the same typical survey missions, inertial systems have a higher 
accuracy when aircraft of the 400 kts speed range are used, i.e. jet- 
propelled aircraft. 
b. Cost and operational effort 
5.7  Atthe stage of technology today, as an order of magnitude comparison, 
the investment cost of inertial systems may be approximately twice or 
three times the cost of doppler systems. 
e = 5.8 In today’s technology, the maintenance cost of inertial systems is still 
high, amounting to approximately 10% of the investment per year. 
Also, survey aircraft may be forced to fly to some far-away country for 
the yearly specialized maintenance of her INS system. 
It is probable that this situation will improve in future. 
: us - 1 : 
€. Comparison of efficiency ) for aerial survey 
5.9 When considering the items 5.1 ... 5.6 (performance and accuracy) and 
the items 5.7 and 5.8 (cost), one arrives at the conclusion that — at the 
state of technology today — doppler-based systems are preferable over 
inertial-based systems in propeller-driven aircraft, for survey navigation. 
In jet-propelled aircraft, inertial-based systems have a higher navigation 
accuracy; this, however, is obtained at appreciably higher cost. In some 
cases, the difference in investment may not have a predominant effect 
on the total investment because jet aircraft ask for a high investment 
anyhow; the maintenance aspect, however, may be a more serious 
consideration. 
€ - 5.10 An additional advantage of inertial-based systems over doppler-based 
systems is the fact that inertial is capable of determining the three 
attitude angles — elements of exterior orientation of the aerial camera 
1) the degree of “efficiency” being defined as to be the value of the ratio "quantity 
of benefit derived from the use of a system’ over “extra investment and/or extra 
operational cost needed to acquire and/or to operate that system’.