US 4,549,184 A · Moving target ordnance control

Abstract

In an airborne radar system, moving ground targets are identified on a cathode ray tube (CRT) display and their motion tracked to allow precise delivery of air-to-ground weapons. Target location errors, due to the effect of target motion upon the doppler frequency of the received signals, and consequent angle measurement ambiguities introduced by the presence of clutter are significantly reduced. The target's radial velocity with respect to the electrical boresight of the system antenna is determined and a corresponding frequency adjustment is made to the processed signal in order to accurately locate the target on the display to lie in precise correspondence to its displayed stationary surroundings. The determination of target radial velocity also provides the measurement of target radial velocity also provides a precise interferometer antenna referenced azimuth angle estimate to be used for relative range and azimuth weapon guidance, independent of usually large angle errors arising from clutter effects within the field of view of the antenna, and of other hardware and navigational error sources associated with absolute angle measurement systems.

Claims17

Dependent claims

In conjunction with an AMTI synthetic aperture radar system having an interferometer antenna and a range versus azimuth angle display, a method for determining with improved accuracy the azimuth angle of a moving target having a radial component of velocity relative to the electrical boresight of the interferometer antenna comprising the steps of:

(a) calculating the radial component of velocity Vm of the moving target;
(b) shifting the observed net doppler frequency of the moving target by the quantity ##EQU8## where .lambda. is the operating wavelength of the radar system, so that the moving target resides in a doppler cell whose frequency corresponds to that of clutter in the immediate vicinity of the moving target;
(c) plotting the data obtained from interleaved interferometric measurements on the received signals from stationary clutter and fixed targets as doppler frequency versus interferometer azimuth angle;
and
(d) obtaining from the plot of doppler frequency versus interferometer azimuth angle for the stationary clutter and fixed targets the azimuth angle relative to the electrical boresight of the antenna of clutter in the immediate vicinity of the moving target.

2 more elements

In combination with an AMTI synthetic aperture radar system having an interferometer antenna and a range versus azimuth angle display, signal processing means for determining with improved accuracy the azimuth angle of a moving target having a radial component of velocity relative to the electrical boresight of the interferometer antenna comprising:

(a) means for calculating the radial component of velocity Vm of the moving target, and shifting the observed net doppler frequency of the moving target by the quantity ##EQU17## where .lambda. is the operating wavelength of the radar system, so that the moving target resides in a doppler cell whose frequency corresponds to that of clutter in the immediate vicinity of the moving target;
(b) means for plotting the data obtained from interleaved interferometric measurements on the received signals from stationary clutter and fixed targets as doppler frequency versus interferometer azimuth angle;
and
(c) means for obtaining from the plot of doppler frequency versus interferometer azimuth angle for the stationary clutter and fixed targets the azimuth angle relative to the electrical boresight of the antenna of clutter in the immediate vicinity of the moving target.

1 more element

In combination with an AMTI synthetic aperture radar system including a three phase center interferometer antenna operatively connected to the input to a two channel receiver and processing system, and a real-time display of range versus azimuth angle operatively connected to the output of said two channel receiver and processing system, signal processing means for determining with improved accuracy the azimuth angle of a moving target having a radial component of velocity relative to the electrical boresight of the interferometer antenna comprising:

(a) means for compensating for phase variations in the received signals due to motion of the AMTI radar bearing aircraft, said motion compensating means including means for accurately determining the component of aircraft velocity parallel to the antenna boresight direction V cos .theta. in order to motion compensate the received signals on a pulse-to-pulse basis;
(b) means for calculating the radial component of velocity Vm of the moving target, said velocity calculating means including:
(1) means for estimating the component of aircraft velocity perpendicular to the antenna boresight direction V sin .theta. from a composite plot generated by averaging the slopes of the individual plots of doppler frequency versus interferometer azimuth angle of each of the range bins processed;
(2) means for determining the phase advance .phi. from a series of vector substractions, .DELTA.1=A2-A1 and .DELTA.2=A3-A2, where A1, A2, and A3 are coherent integration vector sums and setting .phi.=.intg., where .intg. is the measured phase angle between .DELTA.1 and .DELTA.2;
and
(3) means for calculating the value of Vm from the expression ##EQU18## where .lambda. is the operating wavelength of the radar and d is the spacing between the interferometer antenna phase centers;
and for shifting the observed net doppler frequency of the moving target by the quantity ##EQU19## so that the moving target resides in a doppler cell whose frequency corresponds to that of clutter in the immediate vicinity of the moving target;
(c) means for plotting the data obtained from interleaved interferometric measurements on the received signals from stationary clutter and fixed targets as doppler frequency versus interferometer azimuth angle;
and
(d) means for obtaining from the plot of doppler frequency versus interferometer azimuth angle for the stationary clutter and fixed targets the azimuth angle relative to the electrical boresight of clutter in the immediate vicinity of the moving target.

7 more elements

Dependencies are inferred from the claim text.

Moving target ordnance control

Life of this patent

Moving target ordnance control

Life of this patent

Abstract

Claims17