SONAR AND RADAR 



equation which will evaluate the combination of these 

 four important factors. Such an index should have a 

 high value for the most efficient systems and should be 

 roughly proportional to the relative efficiencies of the 

 various systems of echolocation that we compare. As 

 will become clear a Uttle later, this is not as simple as 

 it might seem, but the process of attempting to define 

 such an index, and then modifying it as may seem nec- 

 essary, will in itself prove to be helpful in calling atten- 

 tion to the various quantitative considerations that are 

 important for echolocation. 



TABULAR COMPARISONS OF BATS AND RADAR 



AN/APS - 10 



radar 

 system 



Big 



brown 

 bat 



Target detected 

 Target diameter, d 



(cm) 

 Range of detection, R 



(cm) 

 Weight of apparatus, W 



(grams) 

 Emitted power, P 



(watts) 

 R/PWd 

 RVPWd^ 

 RVPWd^ 



Airplane Insect 



300 



8X10^ 



9X10* 



10* 



2.9 X 10-^ 



5 X 10^3 



5.5 X 108 



200 

 0.1 



Little 



brown 



bat 



Wire 



1.8 X 10-2 



90 



0.05 



10-5 10-6 



2 X 108 iQii 



1.6X10^5 3.8X10^^ 

 1.6X1015 1.2X1022 



The above table Usts the range of detection, R, 

 the diameter of the target, d, (both in centimeters), the 

 power emission, P (watts) , and the weight of the system, 

 W (grams). For the bats, 10 per cent of the weight of a 

 fasting animal seems a generous allowance for the lar- 



123 



