This document describes a practical system for a user to determine observer-to-aircraft distances. These observer-toaircraft distances can be either closest point of approach (CPA) distances during field measurements or overhead distances during acoustic certification tests. The system uses a digital camera to record an image of the subject aircraft. A method of using commercial software to obtain the distance from such an image is presented. Potential issues which may affect accuracy are discussed.
This revised version replaces AIR902 issued May 1966. This version discusses the use of digital imaging equipment and software which did not exist when the previous AIR902 was written. This version also contains added information on using the distance determination during acoustic tests. The original version used the phrase ‘Minimum Distance’ in the title, but the techniques discussed in this AIR allow users to determine general distances, not just minimums.
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