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Determining Relative Position and Separation of Two Aircraft

IP.com Disclosure Number: IPCOM000093377D
Original Publication Date: 1967-Sep-01
Included in the Prior Art Database: 2005-Mar-06
Document File: 3 page(s) / 40K

Publishing Venue

IBM

Related People

Gruenberg, EL: AUTHOR

Abstract

The system permits a given aircraft A to establish relative position in bearing, relative velocity at this bearing, relative altitude, and range of another aircraft B within its proximity. It provides such information to the pilot of aircraft A and requires only that a cooperative altimeter beacon is provided on each aircraft. This system is also capable of providing the speed and heading of the aircraft B, i.e., flight path, when used in conjunction with an iterative computer procedure.

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Determining Relative Position and Separation of Two Aircraft

The system permits a given aircraft A to establish relative position in bearing, relative velocity at this bearing, relative altitude, and range of another aircraft B within its proximity. It provides such information to the pilot of aircraft A and requires only that a cooperative altimeter beacon is provided on each aircraft. This system is also capable of providing the speed and heading of the aircraft B,
i.e., flight path, when used in conjunction with an iterative computer procedure.

A narrow beam antenna on aircraft B illuminates the ground directly, i.e., vertically below it. Aircraft A receives signals from the ground point and establishes aircraft B's bearing from the received Doppler frequency shift. If stabilized frequencies are used, this measurement can be made by comparison with a standard frequency in aircraft A. If not, it can be established by comparison with a frequency received by direct path from aircraft B.

The received Doppler shift from ground point G below aircraft B is different from that received directly from aircraft B. The direct Doppler is a measure of the closing rate of the aircraft and includes all motions of aircrafts A and B. The Doppler from G, however, is only a function of the motion of aircraft A with respect to the ground spot. If aircraft B runs parallel to earth, the frequency of the illumination is not shifted from that of aircraft B's transmitter. If the aircraft B is rising, the small error can readily be compensated for. Thus, aircraft A can measure its own velocity with respect to G.

The bearing angle is determined from the Doppler frequency shift of a signal transmitted from aircraft B. A signal at frequency f is transmitted over a highly directional antenna from aircraft B vertically to the ground below. This signal is received in aircraft A and the Doppler shift is measured. It is assumed that the two aircrafts are at the same altitude. From the elevation and plan views, the Doppler shift is given by delta f(B)= (2V(Ar)/lambda(B) Cos alpha, where lambda(B) = the wavelength of the signal transmitted and alpha = the angle shown. Angle alpha, then the two aircrafts are at the same altitude, is given by alpha = tan/-1/ (h/r), where h is the altitude above the ground. The bearing angle is obtained from Omega(A) = Cos/-1/ (V(Ar)/V(A)), since the velocity V(A) is known.

A one-way ranging system can be combined with the bearing measurement. This system computes r...