Radar and ARPA Manual

9 ARPA

—

accuracy and

errors

9.1 Introduction

Errors present in the data displayed on the ARPA screen

or by the alphanumeric read-out will affect decision

making. The observer must therefore have a knowledge

of the level of accuracy that can be expected and the

errors which will affect it. It is not a simple matter to

specify the accuracy because it depends on, among other

Table 9.1 ARPA accuracy values (95% probability)

required after one minute

Scenario Relative

course

Relative

speed

CPA

(degrees) (knots) (nautical

miles)

1

2

3

4

11

7

14

15

2.8

0.6

2.2

1.5

1.6

1.8

2.0

things, the geometry of the plotting triangle. For this

reason, the IM