US 5,212,490 A · Echo ranging system for detecting velocity and range of targets using composite doppler invariant-like transmissions with suppression of false targets

Abstract

False target (reverberation, clutter, etc.) detection is suppressed in an echo ranging system (sonar or radar) in which target velocity and range are measured using a composite Doppler invariant-like signal having at least two segments, such as are present in a "rooftop" or "vee" HFM signal, such composite signal having an ambiguity function with two or more ridge lines of different slopes that intersect along the zero-velocity time axis. A bank of matched filters provides a distribution of outputs which has an ambiguity function-like character with intersecting pairs of ridge lines, the intersecting points of said pairs characterizing the range and velocity of the echo returns. This distribution is adjusted so that the intersecting ridge lines of each pair have equal and opposite slopes with respect to the time axis. In particular, fixed reverberators, which would have ridge lines intersecting on the zero-velocity time axis, would be symmetrical about this axis. A target with velocity v would present ridge lines intersecting along the v-velocity time axis and be symmetrical about that axis. Thus, the reverberation and the moving target would each have crossed ridge lines whose characteristic intersecting patterns would each exhibit symmetries, but about separate and distinct axes. False targets, including clutter and reverberation, are suppressed by subtracting from the adjusted output distribution, a replica thereof, folded (rotated) 180.degree. about a time axis containing the intersection of the ridge line pair corresponding to the false target which is to be suppressed. The rotation and subtraction of the replica from the adjusted distribution provides a set of outputs from which the real target velocity and range can be determined. The rotation-subtraction process can be implemented on an on-going basis to suppress a plurality or continuum of false targets and to achieve a desired width of a Doppler notch covering an arbitrary range of velocities.

Claims22

Dependent claims

An echo ranging system for determining simultaneously the range and velocity of moving targets and for suppressing unwanted returns including reverberation, clutter and returns from false targets, said system comprising:

means for transmitting a composite signal comprised of at least two segments, each having Doppler invariant-like characteristics as well as a time-bandwidth product greater than unity, said composite signal also having an ambiguity function in velocity-time space, said space having velocity and time axes that are perpendicular, said ambiguity function having at least a first pair of ridge lines which intersect along the zero-velocity time axis, each ridge line of said at least first pair having a different slope with respect to said zero-velocity time axis;
means for receiving echo returns from said transmitted signal;
a bank of matched filters;
means for passing said echo returns through said bank of matched filters to provide a distribution of outputs which characterize the range and velocity properties of said echo returns;
detection means operative upon said outputs for providing an ambiguity function-like detected output distribution in velocity-time space, said output distribution being formed by intersecting second pairs of ridge lines, said intersections occurring uniquely in time and velocity to define individually the range and velocity of said echo returns;
means for adjusting at least one ridge line of each said second, intersecting ridge line pair of said distribution to make the slopes of said ridge lines of said second, intersecting ridge line pairs equal and opposite with respect to the time axis to provide an adjusted output distribution;
means for providing continuously a replica of said adjusted output distribution rotated 180.degree. about the time-axis containing the intersection of a ridge line pair corresponding to an unwanted return;
means for combining said rotated adjusted replica of said output distribution with said adjusted output distribution in time alignment to obtain a combined distribution in which said unwanted return is suppressed;
and
means responsive to said combined distribution for providing the range and velocity of said moving targets.

7 more elements

An echo ranging system for determining the range and velocity of moving targets, and for suppressing unwanted returns as from reverberation, clutter, or false targets, including reverberation or false targets appearing with a velocity v, where v may be zero or nonzero, said system comprising:

means for transmitting a signal of total duration T having a time-bandwidth product greater than unity and an ambiguity function that is distributed symmetrically about the time axis corresponding to zero velocity in time-velocity space;
means for receiving echo return signals from moving targets as well as unwanted echo return signals from said reverberation, clutter, or false targets appearing with said velocity v, said unwanted return signals having an ambiguity function that is symmetrical about the time axis corresponding to said velocity v in time-velocity space;
a bank of matched filters, each filter of said bank having a signal replica corresponding to a different target velocity;
means for passing said echo return signals through said bank of matched filters to provide a distribution of outputs which characterize the range and velocity of said echo returns;
means for providing continuously a replication of said output distribution rotated 180.degree. about the time axis corresponding to said velocity v;
means for combining said rotated output distribution with said distribution of outputs in time alignment to obtain a combined distribution in which said unwanted returns are suppressed;
and
means responsive to said distribution for providing the range and velocity of said moving targets.

5 more elements

Dependencies are inferred from the claim text.

Echo ranging system for detecting velocity and range of targets using composite doppler invariant-like transmissions with suppression of false targets

Life of this patent

Echo ranging system for detecting velocity and range of targets using composite doppler invariant-like transmissions with suppression of false targets

Life of this patent

Abstract

Claims22