Radar beam sharpening system and method

• US 9,182,482 B2
• Filed: 10/25/2012
• Issued: 11/10/2015
• Est. Priority Date: 10/25/2011
• Status: Active Grant

• Current Assignee: Navico Incorporated (Brunswick Corporation)
• Original Assignee: Navico Holding A.S. (Brunswick Corporation)
• Inventors: Lilburn, Lindsay
• Primary Examiner(s): Sotomayor, John B
• Assistant Examiner(s): WINDRICH, MARCUS E
• Application Number:
  US13/660,599
• Publication Number:
  US 20130307720A1
• Time in Patent Office: 1,111 Days
• Field of Search: 342 25 R- 25 F, 342/41, 342/175
• US Class Current: 1/1
• CPC Class Codes: G01S 13/42 Simultaneous measurement of distance and other co-ordinates indirect measurement G01S13/46
• CPC Class Codes: G01S 13/9027 Pattern recognition for feature extraction
• CPC Class Codes: G01S 7/046 using an intermediate storage device, e.g. a recording/reproducing device
• CPC Class Codes: G01S 7/12 Plan-position indicators, i.e. P.P.I.

Abstract

A radar beam sharpening system for processing a radar video stream of echo return intensities, sampled in range and azimuth. The system uses a signal processor that is configured to apply beam sharpening to the radar video stream and which selectively varies the level of beam sharpening applied as a function of range and/or a land map generated from the radar video stream so as to generate an output selectively beam sharpened radar video stream.

Claims

1. A radar beam sharpening system for processing a radar video stream of echo return intensities, sampled in range and azimuth, comprising:

a signal processor configured to apply beam sharpening to the radar video stream and to selectively vary the level of beam sharpening applied to samples of the radar video stream based on their respective ranges so as to generate an output range-dependent beam sharpened radar video stream,

wherein the signal processor is configured to reduce the beam sharpening applied for at least a portion of shorter ranges relative to longer ranges.

2. A radar beam sharpening system according to claim 1 wherein the signal processor is configured to selectively suppress the level of beam sharpening applied relative to a maximum limit of suppression based on the range of the sample of radar video stream being processed.

3. A radar beam sharpening system according to claim 2 wherein the signal processor is configured to apply a higher level of beam sharpening suppression at shorter ranges relative to longer ranges.

4. A radar beam sharpening system according to claim 2 wherein the level of beam sharpening suppression applied to each sample in the radar video stream is selected from a range defined between full suppression in which no beam sharpening is present in the output radar video stream and nil suppression in which full beam sharpening is present in the output radar video stream.

5. A radar beam sharpening system according to claim 1 wherein the signal processor comprises:

a beam sharpener that is configured to receive and process the original radar video stream and generate a beam sharpened radar video stream; and

a mixer configured to blend the original radar video stream with the beam sharpened radar video stream based on a variable mixing ratio that is a function of range of the sample of the radar video steam being processed so as to generate the output range-dependent beam sharpened radar video stream, and wherein the mixing ratio defines the proportions of each of the original radar video stream and beam sharpened radar video stream present in the output range-dependent beam sharpened radar video stream.

6. A radar beam sharpening system according to claim 5 wherein the mixer comprises:

a mixer control function that is configured to determine the range of the sample of the original radar video stream being processed and to generate the variable mixing ratio based on that range;

a first multiplier configured to receive the original radar video stream and multiply that stream by the mixing ratio to generate a first multiplier output stream;

a second multiplier configured to receive the beam sharpened radar video stream and multiply that stream by the inverse of the mixing ratio to generate a second multiplier output stream; and

an adder that is configured to combine the first and second output streams from the multipliers to generate the output range-dependent beam sharpened radar video stream.

7. A radar beam sharpening system according to claim 6 wherein the mixer control function is configured to generate a mixing ratio that varies with range such that the proportion of the beam sharpened radar video stream in the output range-dependent beam sharpened radar video stream is reduced for short ranges relative to longer ranges.

8. A radar beam sharpening system according to claim 6 wherein the mixer control function is configured to generate a variable mixing ratio in a range defined between a first maximum limit representing full beam sharpening suppression applied in which the output range-dependent beam sharpened radar video stream comprises only the original radar video stream and a minimum limit representing nil beam sharpening suppression in which the output range-dependent beam sharpened radar video stream comprises only the beam sharpened radar video stream.

9. A radar beam sharpening system according to claim 1 wherein the signal processor is further configured to selectively vary the level of beam sharpening applied based on a land map generated from the radar video stream.

10. A method of beam sharpening a radar video stream of echo return intensities, sampled in range and azimuth, the method implemented by a programmable signal processor and comprising:

receiving the radar video stream;

applying a selectively variable level of beam sharpening to the samples of the radar video stream based on their respective ranges by reducing the beam sharpening applied for at least a portion of shorter ranges relative to longer ranges; and

outputting a range-dependent beam sharpened radar video stream.

11. A radar beam sharpening system for processing a radar video stream of echo return intensities, sampled in range and azimuth, comprising:

a signal processor configured to apply beam sharpening to the radar video stream and to selectively vary the level of beam sharpening applied to the samples of the radar video stream based on land map data generated from the radar video stream by a land map generator so as to generate an output land map dependent beam sharpened radar video stream, the land map generator being configured to generate land map data indicative of whether a sample of the radar video stream is a land-type target or non-land type target, and wherein the signal processor is configured to reduce the beam sharpening applied to samples corresponding to land-type targets relative to non-land type targets.

12. A radar beam sharpening system according to claim 11 wherein the signal processor is configured to selectively suppress the level of beam sharpening applied relative to a maximum limit based on the land map data associated with the sample of radar video steam being processed.

13. A radar beam sharpening system according to claim 12 wherein the signal processor is configured to apply a higher level of beam sharpening suppression to samples corresponding to land-type targets relative to non-land-type targets as determined from, the land map data.

14. A radar beam sharpening system according to claim 12 wherein the level of beam sharpening suppression applied to each sample in the radar video stream is selected from a range defined between full suppression in which no beam sharpening is present in the output radar video stream and nil suppression in which full beam sharpening is present in the output radar video stream.

15. A radar beam sharpening system according claim 14 wherein the signal processor is configured to apply nil suppression to samples corresponding to non-land-type targets, and a level of suppression to samples corresponding to land-type targets that increases with the intensity of the land-type targets based on the land map data.

16. A radar beam sharpening system according to claim 11 wherein the signal processor comprises:

a beam sharpener that is configured to receive the original radar video stream and generate a beam sharpened radar video stream; and

a mixer configured to blend the original radar video steam with the beam sharpened radar video stream based on a variable mixing ratio that is a function of the land map data generated from the original radar video stream so as to generate the output land map dependent beam sharpened radar video stream, and wherein the mixing ratio defines the proportions of each of the original radar video stream and beam sharpened radar video stream present in the output land map dependent beam sharpened radar video stream.

17. A radar beam sharpening system according to claim 16 wherein the mixer comprises:

a mixer control function that is configured to generate land map data for the sample of the original radar video stream being processed and to generate the variable mixing ratio based on that land map data;

a first multiplier configured to receive the original radar video stream and multiply that stream by the mixing ratio to generate a first multiplier output stream;

a second multiplier configured to receive the beam sharpened radar video stream and multiply that stream by the inverse of the mixing ratio to generate a second multiplier output stream; and

an adder configured to combine the first and second output streams from the multipliers to generate the output land map dependent beam sharpened radar video stream.

18. A radar beam sharpening system according to claim 17 wherein the mixing control function is configured to generate a mixing ratio that varies with the land map data such that the proportion of the beam sharpened radar video stream in the output land map dependent radar video stream is reduced for samples of the radar video stream corresponding to land-type targets relative to non-land-type targets.

19. A radar beam sharpening system according to claim 18 wherein the mixer control function is configured to generate a variable mixing ratio in a range defined between a first maximum limit representing full beam sharpening suppression applied in which the output land map dependent beam sharpened radar video stream comprises only the original radar video stream and a minimum limit representing nil beam sharpening suppression in which the output land map dependent beam sharpened radar video stream comprises only the beam sharpened radar video stream.

20. A radar beam sharpening system according to claim 19 wherein the mixer control function comprises the land map generator that is configured to generate land map data from the original radar video stream, and wherein the land map generator comprises a land map filter that is configured to low pass filter the original radar video stream in range and azimuth to generate a land map filtered radar video stream and the mixing ratio is dependent on the land map filtered radar video stream.

21. A radar beam sharpening system according to claim 20 wherein the land map generator of the mixer control function further comprises a land sensitivity time control (STC) function following the land map filter that is configured to apply STC processing to the land map filtered radar video stream based on an STC threshold profile that defines an echo return intensity threshold over range, the STC threshold profile being optimized for land-type target detection, and the mixing ratio is determined based on the output stream from the STC processing.

22. A radar beam sharpening system according to claim 20 wherein the land map filter comprises a two stage low pass filter comprising firstly an azimuth filter configured to low pass filter the radar video stream in azimuth followed by a range filter configured to low pass filter the azimuth filtered stream from the azimuth filter in range to generate the final land map filtered radar video stream.

23. A radar beam sharpening system according to claim 22 wherein the land map filter further comprises a comparator between the azimuth filter and range filter, the comparator being configured to select the minimum value of the original radar video stream and the azimuth filtered stream as input into the range filter, and wherein the azimuth filter is a median filter and the range filter is an averaging filter.

24. A radar beam sharpening system according to claim 11 wherein the signal processor is further configured to selectively vary the level of beam sharpening applied based on range.

25. A method of beam sharpening a radar video stream of echo return intensities, sampled in range and azimuth, the method implemented by a programmable signal processor comprising:

receiving the radar video stream;

applying a selectively variable level of beam sharpening to the samples of the radar video stream based on land map data generated from the radar video stream by a land map generator that is configured to generate land map data indicative of whether a sample of the radar video stream is a land-type target or non-land type target, and reducing the beam sharpening applied to samples corresponding to land-type targets relative to non-land type targets; and

outputting a land map dependent beam sharpened radar video stream.