Ground clutter suppression technique

• US 4,628,318 A
• Filed: 12/02/1983
• Issued: 12/09/1986
• Est. Priority Date: 12/02/1983
• Status: Expired due to Term

• Current Assignee: Rockwell International Corporation
• Original Assignee: Rockwell International Corporation
• Inventors: Alitz, Orville J.
• Primary Examiner(s): Tarcza, Thomas H.
• Assistant Examiner(s): Hayes, Jr., Donald E.
• Application Number:
  US06/557,679
• Time in Patent Office: 1,103 Days
• Field of Search: 343/5 W, 343/17.1 R, 343/7.7, 343/5 DP, 343/5 CE, 343/7 A
• US Class Current: 342/26.00D
• CPC Class Codes: G01S 13/5242 with means for platform motion or scan motion compensation, e.g. airborne MTI
• CPC Class Codes: G01S 13/951 ground based
• CPC Class Codes: Y02A 90/10 Information and communication technologies [ICT] supporting adaptation to climate change, e.g. for weather forecasting or climate simulation

Abstract

A ground clutter suppression technique is disclosed utilizing two parallel return signal processing paths, both utilizing linear-to-logarithmic conversion capability and one having a signal delay capability for one pulse repetition. The outputs are subtracted and are subsequently compared with a factor related to the root-mean-square (rms) of two deviation inputs, one input functionally related to apparatus limitations and one deviation input functionally related to antenna position (step between samples) for each signal received. The Doppler frequency standard deviation inputs are then summed rms and used to select an amplitude standard deviation which is compared with the amplitude difference between successive return signals. Thereafter, the logic decision output is operated on utilizing a digital filter to essentially eliminate ground clutter or small variance (PRF to PRf) return signals from the display.

Claims

1. In a pulsed Doppler radar, a ground clutter identification circuit comprising:

a bifurcated parallel return signal processing circuit, one branch having a signal delay capability and both branches having linear-to-logarithmic conversion capability and respective outputs;

a deviation generator circuit for generating at least one deviation input functionally related to apparatus limitations for each signal received; and

means for summing said outputs of said processing circuit, coupled to both branches and to said deviation generator circuit.

2. A circuit as in claim 1 further comprising a second deviation generator for generating at least one deviation input functionally related to antenna positioning for each signal received, in parallel with said first deviation generator, and coupled to said means for summing the outputs of said processing circuit.

3. A circuit as in claim 2 further comprising means coupled to said deviation generators for summing and correlating said deviation inputs.

4. A circuit as in claim 3 further comprising means, coupled to said means for summing outputs of said processing circuit and coupled to said means for summing and correlating said deviation inputs, for indicating signals exceeding a predetermined threshold.

5. A circuit as in claim 4 further comprising a digital filter coupled to said means for indicating signals, for determining the ratio of signals exceeding a predetermined threshold to the number of samples and thereby indicate clutter as a function of said ratio.

6. A circuit as in claim 4 further comprising means for detecting signal magnitude and generating a noise alarm as a function of correlated signal magnitude above a predetermined threshold level.

7. A circuit as in claim 4 further comprising an alien radar blanking circuit for detecting large signal magnitudes relative to average returns, and for so indicating at an output.

8. In a pulsed Doppler radar, a ground clutter indication circuit comprising:

a deviation generator for generating in parallel at least one deviation input functionally related to apparatus limitations for each signal received, and for generating at least one deviation input functionally related to antenna scan position and rate for each signal received; and

means coupled to said deviation generator for summing and correlating said deviation inputs.

9. A circuit as in claim 8 further comprising:

a bifurcated parallel return signal processing circuit, one branch having a signal delay capability and both branches having linear-to-logarithmic conversion capability; and

means for summing the outputs of said processing circuit coupled thereto, and coupled to said means for summing and correlating said deviation outputs.

10. A circuit as in claim 9 further comprising means, coupled to said means for summing outputs of said processing circuit and coupled to said means for summing and correlating said deviation inputs, for indicating signals exceeding a predetermined threshold.

11. A circuit as in claim 10 further comprising a digital filter, coupled to said means for indicating signals, for determining the ratio of signals exceeding a predetermined threshold to the number of samples and thereby indicate clutter as a function of said ratio.

12. A circuit as in claim 10 further comprising means for detecting signal magnitude and generating a noise alarm as a function of correlated signal magnitude above a predetermined threshold level.

13. A circuit as in claim 10 further comprising an alien radar blanking circuit for detecting single large signal magnitudes over a sequence of returns, and for so indicating at an output.

14. A digital pulse radar apparatus for use with an antenna and having a ground clutter suppression circuit and a plurality of range cells comprising in combination:

a. first means for receiving a first sequentially ordered plurality of returned signals, said signals received in a cyclic manner controlled by the pulse repetition rate of said apparatus;

b. second means, coupled to said first means, for converting said first ordered plurality of signals from a linear to a logarithmic representation;

c. third means, coupled to said first means, for delaying said first ordered plurality of signals for one pulse repetition;

d. fourth means, coupled to said third means, for converting said delayed plurality of signals from a linear to a logarithmic representation;

e. fifth means, coupled to said second means and to said fourth means, for summing said converted first ordered plurality of signals and said converted delayed plurality of signals;

f. sixth means, coupled to said first means, for generating a signal deviation as a fixed function of the capability of said apparatus and providing a first deviation output;

g. seventh means for coupling to said antenna and for generating a signal deviation as a variable function of antenna scan position, scan rate and antenna beamwidth for each of said plurality of range cells, and providing a second deviation output;

h. an eighth means, coupled to said sixth means and to said seventh means, for summing said first deviation output and said second deviation output;

i. ninth means, coupled to said eighth means, for correlating the Doppler frequency standard deviation of said summed deviations to the amplitude standard deviation; and

j. tenth means, coupled to said fifth means and to said ninth means, for summing said summed converted signals with said summed deviations to provide binary outputs indicating which of said received signals exceed a predetermined threshold.

15. An apparatus as in claim 14 further comprising a digital filter, coupled to said tenth means, for determining the ratio of said binary outputs to the number of samples and thereby indicate clutter as a function of said ratio.

16. An apparatus as in claim 15 further comprising means for detecting signal magnitude and generating a noise alarm as a function of correlated signal magnitude above a predetermined threshold level.

17. An apparatus as in claim 15, further comprising an alien radar blanking circuit for detecting single large signal magnitudes over a sequence of returns, and for so indicating at an output.