Radar system and method for detecting and discriminating targets from a safe distance

• US 5,592,170 A
• Filed: 06/06/1995
• Issued: 01/07/1997
• Est. Priority Date: 04/11/1995
• Status: Expired due to Term

• Current Assignee: L-3 Communications Corporation (L3Harris Technologies, Inc.)
• Original Assignee: Jaycor, Inc. (Titan Corporation)
• Inventors: Davis, Herbert T. III, Dunn, Scott A., Price, Robert H.
• Primary Examiner(s): Pihulic, Daniel T.
• Application Number:
  US08/466,938
• Time in Patent Office: 581 Days
• Field of Search: 342/22, 342/90, 342/133, 342/146, 342/27, 342/129, 342/130, 342/131, 342/132, 342/200, 342/201, 342/202, 342/203
• US Class Current: 342/22
• CPC Class Codes: F41H 11/16 Self-propelled mine-clearing vehicles; Mine-clearing devices attachable to vehicles
• CPC Class Codes: G01S 13/24 using frequency agility of carrier wave
• CPC Class Codes: G01S 13/885 for ground probing prospecting or detecting using electromagnetic waves G01V3/12
• CPC Class Codes: G01S 7/2883 using FFT processing
• CPC Class Codes: G01S 7/412 based on a comparison between measured values and known or stored values

Abstract

A frequency-agile, narrow-instantaneous bandwidth radar system detects objects, and discriminates between different types of objects, from a safe stand-off distance. Transmit circuitry transmits a train of continuous wave signals in a multitude of stepped operating frequencies that illuminates the target area. Return signals from the target area are received through at least a pair of spaced-apart receive antennas. Signal receive/processing circuitry coupled to the spaced-apart receive antennas selectively combines and processes the return signals to identify variations in the received signals indicative of the presence of a specific type of object. At each of the stepped frequencies, the system noise and the clutter of the signals is reduced by averaging and smoothing the incoming data and the cross-power spectrum at each frequency is calculated. Using the information of the power spectra of all frequencies, the Mahalanobis distance is defined and the presence and classification of a target is determined. Using the information of the cross-power spectra of all frequencies, the location of the mine is determined by the azimuth angle and echo time.

Claims

1. A method of detecting the presence of a buried object within a target area from a probing location that is a prescribed stand-off distance away from the target area, the method comprising the steps of:

(a) irradiating the target area with a plurality of incident pulses of microwave power from the probing location, the incident pulses having a prescribed waveform signature;

(b) receiving a plurality of return pulses of microwave power reflected from the target area at two spaced-apart locations, the two spaced-apart locations having a prescribed orientation relative to the probing location; and

(c) processing the return pulses received at the two spaced-apart locations in step (b) to determine the presence and location of the object.

2. The method of claim 1 wherein the step of irradiating the target area with an incident pulse of microwave power from the probing location further comprises the steps of:

(a1) producing a frequency adjustable continuous wave signal over a range of frequencies in prescribed increments;

(a2) modulating the continuous wave signal to produce short duration radar pulses to be transmitted;

(a3) transmitting the short duration radar pulses towards the target area;

(a4) adjusting the continuous wave signal frequency by the preselected increment; and

(a5) repeating steps (a2) through (a4) concurrently with the step (b) and step (c) until the range of frequencies have been transmitted.

3. The method of claim 1 wherein the step of receiving the plurality of return pulses of microwave power reflected from the target area at two spaced-apart locations further comprises the steps of:

(b1) receiving the plurality of return pulses reflected from the target area;

(b2) detecting In-phase and Quadrature signals within each return pulse at each of the two spaced-apart locations;

(b3) conditioning the In-phase and Quadrature signals for each returned pulse;

(b4) digitizing the conditioned In-phase and Quadrature signals for each return pulse; and

(b5) reducing system noise and clutter present in the digitized signals to produce output signals.

4. The method of claim 1 wherein the step of processing the plurality of return pulses received at the two spaced-apart locations to determine the presence and location of the object further comprises the steps of:

(c1) computing a power spectrum and a cross-correlation of the plurality of return pulses;

(c2) computing a decision statistic based on the power spectrum of the return pulses over a range of frequencies near a resonant frequency of the object to ascertain whether the particular object is present within the target area; and

(c3) determining a range and an azimuth angle of the particular object present within the target area to ascertain the location of the detected object.

5. The method of claim 4 further comprising the steps of:

(c4) identifying a particular set of attributes associated with the power spectrum of the return pulses representative of a particular target type; and

(c5) comparing the particular set of attributes associated with the power spectrum of the particular object present within the target area with a library of stored identification data representative of the particular set of attributes associated with the power spectrum of prescribed objects to ascertain the type of object detected.

6. The method of claim 1 wherein the probing location is contained on a mobile vehicle.

7. A method of detecting the presence of an object within a target area from a probing location that is a prescribed stand-off distance away from the target area, the method comprising the steps of:

(a) producing a frequency adjustable continuous wave signal over a range of frequencies in prescribed increments;

(b) modulating the continuous wave signal to produce short duration radar pulses to be transmitted;

(c) transmitting the short duration radar pulses from the probing location towards the target area;

(d) receiving the plurality of return pulses reflected from the target area at two spaced-apart locations, the two spaced-apart locations having a prescribed orientation relative to the probing location;

(e) detecting In-phase and Quadrature signals within each return pulse at each of the two spaced-apart locations;

(f) conditioning the In-phase and Quadrature signals for each returned pulse;

(g) digitizing the conditioned In-phase and Quadrature signals for each return pulse;

(h) reducing system noise and clutter present in the digitized signals to produce output signals;

(i) adjusting the continuous wave signal frequency by the preselected increment;

(j) processing the output signals to determine the presence and location of the object; and

(k) repeating steps (b) through (j) until the range of frequencies have been transmitted.

8. The method of claim 7 wherein the step of processing the output signals to determine the presence and location of the object further comprises the steps of:

(l) computing a power spectrum and a cross-correlation of the output signals;

(m) computing a decision statistic based on the power spectrum of the output signals over the range of frequencies to ascertain whether the particular object is present within the target area; and

(n) determining a range and an azimuth angle of the particular object present within the target area to ascertain the location of the detected object.

9. The method of claim 8 further comprising the steps of:

(o) identifying a particular set of attributes associated with the power spectrum of the output signals representative of a particular target type; and

(p) comparing the particular set of attributes associated with the power spectrum of the particular object present within the target area with a library of stored identification data representative of the particular set of attributes associated with the power spectrum of prescribed objects to ascertain the type of object detected.

10. A radar system comprising:

frequency-agile transmitting means for transmitting an incident pulse of microwave power having an adjustable frequency;

receiving means for receiving a return pulse of the microwave power from a target area, the return pulse representing the reflection of the incident pulse of microwave power from at least one object located within the target area, the receiving means including means for receiving the return pulse at a plurality of spaced-apart locations relative to the location of the transmitting means;

first processing means for processing the return pulse received at each of the plurality of spaced-apart locations in respective processing channels, and for producing output signals based on said processing; and

second processing means responsive to the output signals for indicating the presence and location of a particular type of object within the target area.

11. The radar system as set forth in claim 10 wherein the receiving means includes first and second receiving antennas spaced a prescribed distance apart, and wherein the frequency-agile transmitting means includes a transmit antenna, and further wherein the transmit antenna is positioned substantially equidistant from each of the receiving antennas.

12. The radar system as set forth in claim 11 wherein the transmit antenna and the first and second receiving antennas are mounted to the same support structure.

13. The radar system as set forth in claim 12 wherein the support structure is portable.

14. The radar system as set forth in claim 11 wherein the frequency-agile transmitting means includes first and second transmit antennas spaced a prescribed distance apart and having a fixed relationship relative to the first and second receiving antennas.

15. The radar system as set forth in claim 14 wherein the first transmit antenna and the first receiving antenna comprise the same antenna, and wherein the second transmit antenna and the second receiving antenna comprise the same antenna.

16. The radar system as set forth in claim 10 wherein the first processing means further comprises an In-phase and Quadrature detector means for detecting In-phase and Quadrature signals within the return pulse, means for conditioning the In-phase and Quadrature signals, and means for digitizing the conditioned In-phase and Quadrature signals.

17. The radar system as set forth in claim 10 wherein the second processing means further includes means for reducing system noise.

18. The radar system as set forth in claim 17 wherein the second processing means further includes means for reducing system clutter.

19. The radar system as set forth in claim 10 wherein the second processing means further includes means for computing a cross-power spectrum and a cross-correlation of the output signals.

20. The radar system as set forth in claim 19 wherein the second processing means further includes statistical means for computing a decision statistic based on the cross-power spectrum of the output signals over a range of frequencies near a resonant frequency of a particular target type, the decision statistic providing an indication as to whether the particular target type is present within the target area.

21. The radar system as set forth in claim 20 wherein the second processing means further includes identification means for identifying a particular set of attributes associated with the cross-power spectrum of the output signals representative of a particular target type.

22. The radar system as set forth in claim 21 wherein the second processing means further comprise:

storage means for storing identification values representative of the particular set of attributes associated with the cross-power spectrum of particular target types; and

comparison means for comparing the particular set of attributes associated with the cross-power spectrum of the identified target with the stored identification values.

23. The radar system as set forth in claim 20 wherein the second processing means further includes location identification means for identifying a range and an azimuth angle of the particular target present within the target area.

24. Detection apparatus for detecting the presence of an object within a target area from a probing location located a prescribed stand-off distance away from the target area comprising:

irradiating means for irradiating the target area with an incident pulse of microwave power from the probing location, the pulse having a prescribed waveform signature;

receiving means for receiving a return pulse signal of microwave power reflected from the target area at two spaced-apart locations, the two spaced-apart locations having a prescribed orientation relative to the probing location;

receiving circuitry means for processing the return pulse received at each of the plurality of spaced-apart locations in respective processing channels, and for producing output signals therefrom; and

processing means responsive to the output signals for statistically determining whether the return pulse signal thus received indicates the presence of an object within the target area, and if so, the location of the object.

25. The detection apparatus as set forth in claim 24 wherein the processing means further comprises means for reducing system noise and clutter in the output signals.

26. The detection apparatus as set forth in claim 25 wherein the processing means further comprises means for computing a cross-power spectrum and a cross-correlation of the output signals.

27. The detection apparatus as set forth in claim 26 wherein the processing means further includes statistical means for computing a decision statistic based on the cross-power spectrum of the output signals over a range of frequencies near a resonant frequency of a particular object, the decision statistic providing an indication as to whether the particular object is present within the target area.

28. The detection apparatus as set forth in claim 27 wherein the processing means further includes location identification means for identifying a range and an azimuth angle of the particular object present within the target area.