Method and apparatus for creating and processing universal radar waveforms

• US 7,800,529 B2
• Filed: 02/05/2008
• Issued: 09/21/2010
• Est. Priority Date: 02/05/2008
• Status: Active Grant

• Current Assignee: Arete Associates
• Original Assignee: Arete Associates
• Inventors: Pohlman, Matthew Michael, Farris, Michael Howard, Burri, Jeremy Francis, Potter, Randall Edward
• Primary Examiner(s): Tarcza; Thomas H
• Assistant Examiner(s): Brainard; Timothy A
• Application Number:
  US12/026,508
• Publication Number:
  US 20090195442A1
• Time in Patent Office: 959 Days
• Field of Search: 342/174
• US Class Current: 342/194
• CPC Class Codes: G01S 13/9029 specially adapted for moving target detection within a single SAR image or within multiple SAR images taken at the same time
• CPC Class Codes: G01S 13/904 SAR modes
• CPC Class Codes: G01S 7/2923 based on data belonging to a number of consecutive radar periods

Abstract

A new approach to radar imaging is described herein, in which radar pulses are transmitted with an uneven sampling scheme and subsequently processed with novel algorithms to produce images of equivalent resolution and quality as standard images produced using standard synthetic aperture radar (SAR) waveform and processing techniques. The radar data collected with these waveforms can be used to create many other useful products such as moving target indication (MTI) and high resolution terrain information (HRTI). The waveform and the correction algorithms described herein allow the algorithms of these other radar products to take advantage of the quality Doppler resolution.

Claims

1. A method for processing a waveform comprising:

receiving a first data set having a plurality of values based on a radar waveform return from a set of transmitted radar pulses in which the time separation between at least two neighboring pulses is at least equal to twice the shortest time separation between all of the other neighboring pulses in the set; and

creating a second data set comprising the first data set minus at least one significant value from the first data set and its effects on other values within the first data set.

2. The method of claim 1, further comprising:

creating a third dataset comprising the at least one significant value from the first data set; and

combining the second and third datasets.

3. The method of claim 1, wherein the first data set comprises a plurality of transformed values.

4. The method of claim 3, wherein the plurality of transformed values are frequency values.

5. The method of claim 1, wherein the significant values comprise peak values in a frequency domain.

6. The method of claim 1, wherein the plurality of values comprise an uneven sampling pattern.

7. The method of claim 1 wherein the second data set comprises a number of peak values from the first data set chosen based on a predetermined selection criteria.

8. The method of claim 7, wherein the predetermined selection criteria is a threshold.

9. The method of claim 1, further comprising determining the effects of the at least one significant value by calculating a plurality of propagated effects from the at least one significant value.

10. The method of claim 1 wherein the time separation between at least two neighboring pulses is at least equal to four times the shortest time separation between all of the other neighboring pulses in the set.

11. A computer-program product comprising:

computer-readable storage medium comprising codes executable by at least one computer to implement a method for processing a waveform, comprising;

code for receiving a first data set having a plurality of values based on a radar waveform return from a set of transmitted radar pulses in which the time separation between at least two neighboring pulses is at least equal to twice the shortest time separation between all of the other neighboring pulses in the set; and

code for creating a second data set comprising the first data set minus at least one significant value from the first data set and its effects on other values within the first data set.

12. The computer-program product of claim 11, wherein the computer-readable medium further comprising:

code for creating a third dataset comprising the at least one significant value from the first data set; and

code for combining the second and third datasets.

13. The computer-program product of claim 11, wherein the first data set comprises a plurality of transformed values.

14. The computer-program product of claim 13, wherein the plurality of transformed values are frequency values.

15. The computer-program product of claim 11, wherein the significant values comprise peak values in a frequency domain.

16. The computer-program product of claim 11, wherein the plurality of values comprise an uneven sampling pattern.

17. The computer-program product of claim 11, wherein the second data set comprises a number of peak values from the first data set chosen based on a predetermined selection criteria.

18. The computer-program product of claim 17, wherein the predetermined selection criteria is a threshold.

19. The computer-program product of claim 11, wherein the computer-readable medium further comprising code for determining the effects of the at least one significant value by calculating a plurality of propagated effects from the at least one significant value.

20. The computer-program product of claim 11 wherein the time separation between at least two neighboring pulses is at least equal to four times the shortest time separation between all of the other neighboring pulses in the set.

21. A method for processing a waveform comprising:

receiving a first data set comprising a plurality of transformed values of a set of transmitted radar pulses in which the time separation between at least two neighboring pulses is at least equal to twice the shortest time separation between all of the other neighboring pulses in the set;

identifying at least one peak value in the first data set;

creating a peak correction function approximation using the at least one peak value; and

,

removing the peak correction function approximation from the first data set. to create another data set.

22. The method of claim 21, further comprising creating the plurality of transformed values by:

receiving a plurality of samples of the waveform; and

,

performing an FFT on the plurality of samples.

23. The method of claim 22, wherein the temporal relationship between at least three of the samples in the plurality of samples of the waveform is uneven.

24. The method of claim 22, wherein the waveform is represented by a full set of samples, and the plurality of samples contains only a subset of the full set of samples.

25. The method of claim 22, wherein performing the FFT comprises transforming the plurality of samples from a time domain to a frequency domain.

26. The method of claim 21, wherein creating the peak correction function approximation using the at least one peak value comprises creating a collection of peak values having the at least one peak value.

27. The method of claim 21, wherein creating the peak correction function approximation comprises determining any peak effects on the first data set based on the at least one peak value.

28. The method of claim 27, wherein determining any peak effects on the first data set based on the at least one peak value comprises creating a plurality of transformed samples using the at least one peak value.

29. The method of claim 21 wherein the time separation between at least two neighboring pulses is at least equal to four times the shortest time separation between all of the other neighboring pulses in the set.

30. A waveform generator for generating a plurality of pulses to be transmitted comprising:

a processing system configured to generate a binary sequence representing a transmission of pulses from a plurality of pulses, wherein the binary sequence comprises a sampling pattern of a fully transmitted stream of pulses comprising a first underlying pulse repetition frequency, the sampling pattern having a time separation between at least two neighboring pulses that is at least equal to twice the shortest time separation between all of the other neighboring pulses in the sampling pattern; and

,

a transmitter coupled to the processing system, the transmitter configured to transmit a coded sequence of pulses based on the binary sequence.

31. The waveform generator of claim 30, where the coded sequence comprises a temporally coded sequence.

32. The waveform generator of claim 30, where the sampling pattern consists of a sampling pattern chosen from a quadratic residue (QR) pattern and a pseudo-random pattern.

33. The waveform generator of claim 30, where the sampling pattern comprises a second underlying pulse repetition frequency combined with the first underlying pulse repetition frequency.

34. The waveform generator of claim 30, wherein the coded sequence of pulses has a frequency response comprising a narrow main lobe and small sidelobes.

35. The waveform generator of claim 30 wherein the time separation between at least two neighboring pulses is at least equal to four times the shortest time separation between all of the other neighboring pulses in the set.

36. A method for generating a plurality of pulses to be transmitted comprising:

generating a binary sequence representing a transmission of pulses from a plurality of pulses, wherein the binary sequence comprises a sampling pattern of a fully transmitted stream of pulses comprising a first underlying pulse repetition frequency, the sampling pattern having a time separation between at least two neighboring pulses that is at least equal to twice the shortest time separation between all of the other neighboring pulses in the sampling pattern; and

,

creating a coded sequence of pulses based on the binary sequence.

37. The method of claim 36, where the coded sequence comprises a temporally coded sequence.

38. The method of claim 36, where the sampling pattern consists of a sampling pattern chosen from a quadratic residue (QR) pattern, and a pseudo-random pattern.

39. The method of claim 36, where the sampling pattern comprises a second underlying pulse repetition frequency combined with the first underlying pulse repetition frequency.

40. The method of claim 36, wherein the coded sequence of pulses has a frequency response comprising a narrow main lobe and small sidelobes.

41. The method of claim 36 wherein the time separation between at least two neighboring pulses is at least equal to four times the shortest time separation between all of the other neighboring pulses in the set.

42. A method for generating, transmitting, receiving, and processing a plurality of pulses comprising:

generating a binary sequence representing a transmission of pulses from the plurality of pulses, wherein the binary sequence comprises a sampling pattern of a fully transmitted stream of pulses comprising a first underlying pulse repetition frequency, the sampling pattern having a time separation between at least two neighboring pulses that is at least equal to twice the shortest time separation between all of the other neighboring pulses in the sampling pattern;

creating a coded sequence of pulses based on the binary sequence;

transmitting the coded sequence of pulses;

receiving a scattering of the coded sequence of pulses;

receiving a first data set having a plurality of values based on the scattered coded sequence of pulses that are received; and

creating a second data set comprising the first data set minus at least one significant value from the first data set and its effects on other values within the first data set.

43. The method of claim 42 where the sampling pattern comprises a second underlying pulse repetition frequency combined with the first underlying pulse repetition frequency.

44. The method of claim 43 wherein the second data set comprises a number of peak values from the first data set chosen based on a predetermined selection criteria and wherein the predetermined selection criteria is a threshold.

45. The method of claim 42 wherein the time separation between at least two neighboring pulses is at least equal to four times the shortest time separation between all of the other neighboring pulses in the set.

46. A radar system comprising:

a processing system configured to generate a binary sequence representing a transmission of pulses from the plurality of pulses, wherein the binary sequence comprises a sampling pattern of a fully transmitted stream of pulses comprising a first underlying pulse repetition frequency, the sampling pattern having a time separation between at least two neighboring pulses that is at least equal to twice the shortest time separation between any of the other neighboring pulses in the sampling pattern;

a transmitter coupled to the processing system, the transmitter configured to transmit a coded sequence of pulses based on the binary sequence;

a receiver configured to receive a scattering of the transmitted coded sequence of pulses; and

a signal processor configured to process a first data set having a plurality of values based on the scattered coded sequence of pulses that are received and to create a second data set comprising the first data set minus at least one significant value from the first data set and its effects on other values within the first data set.

47. The radar system of claim 46 where the sampling pattern comprises a second underlying pulse repetition frequency combined with the first underlying pulse repetition frequency.

48. The radar system of claim 46 wherein the second data set comprises a number of peak values from the first data set chosen based on a predetermined selection criteria and wherein the predetermined selection criteria is a threshold.

49. The radar system of claim 46 wherein the time separation between at least two neighboring pulses is at least equal to four times the shortest time separation between all of the other neighboring pulses in the set.