82 THE DEVELOPMENT OF WEAPONS SYSTEM REQUIREMENTS 



(Tff = (0.25) (164/) 



= (0.25) (164) (12) = 494 yd = 0.25 n.mi. (independent of range). 



Several factors act to make the effective errors somewhat larger than the 

 basic errors given in Equation 2-5. 



Ouantization Errors. Errors may be introduced by the process of 

 quantizing or "rounding off" measured values of range and angle. This is 

 done both at the AEW radar and in the CIC computer in order to minimize 

 the amount of data which must be processed and transmitted over the as- 

 sociated data links. 



The process may be visualized as follows. The space around a reference 

 point (in this case either the AEW aircraft or the CIC) is broken into "cells" 

 of arbitrary size and shape. An object anywhere in one of the cells is as- 

 signed a position description corresponding to the position of the center of 

 the cell. This process introduces rms errors which are approximately one- 

 quarter of the cell dimensions. These errors are independent of the meas- 

 urement errors. Thus, if the quantization level (cell size) of the AEW 

 system is chosen to be equal to the rms measurement errors (1.25° and 0.25 

 n.mi. in our case), the equivalent rms error in the AEW data will be in- 

 creased by only about 4 per cent. 



The insensitivity of the equivalent errors to the quantization level of the 

 foregoing example shows that coarser range quantization could be employed 

 if desired. For example, if the space around CIC were broken into cells 1 mi. 

 on a side, the equivalent rms range error would be increased by about 40 

 per cent to a value of 0.35 n.mi. when the polar data from the AEW system 

 were transformed to rectangular coordinates in CIC. 



Because the angle measurement is considerably coarser than the range 

 measurement, the 1-n.mi. CIC data quantization cells would make almost 

 no contribution to the rms angular error data received from the AEW air- 

 craft. Accordingly, the following quantization levels may be chosen as 

 reasonable: 



AEW: Azimuth 1.25° 



Range 0.25 n.mi. 



CIC: X coordinate 1 n.mi. 



Y coordinate 1 n.mi. 



These levels are compatible with a range resolution requirement of 

 1 n.mi. (Paragraph 2-13). If finer range resolution were to be employed, 

 the CIC quantization levels would have to be reduced accordingly. 



Stabilization Errors. Another important possible source of error is 

 the rolling and pitching motion of the AEW aircraft due to maneuvers and 

 wind gusts. It was required (Paragraph 2-11 and Fig. 2-15) that AEW 



