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A method of controlling a radar system by receiving a radar return signal from a target and generating a range-Doppler target image signature of the target; selecting a spectral line within the range-Doppler target image signature from a modulation feature on the target which includes an effective p

A method of controlling a radar system by receiving a radar return signal from a target and generating a range-Doppler target image signature of the target; selecting a spectral line within the range-Doppler target image signature from a modulation feature on the target which includes an effective point scatterer; providing a range profile for the spectral line; obtaining a reference range profile of a reference point scatterer; determining a difference between a power at a range shorter than a peak corresponding to the modulation feature in the range profile and a power at a corresponding range of the reference range profile; and generating a first control signal or a second control signal arranged to provide or prevent provision of the range-Doppler target image signature based on the difference.

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1. A method of controlling a radar system, the method comprising: a. receiving a radar return signal from a target and generating a range-Doppler target image signature of the target;b. selecting a spectral line within the range-Doppler target image signature from a modulation feature on the target

1. A method of controlling a radar system, the method comprising: a. receiving a radar return signal from a target and generating a range-Doppler target image signature of the target;b. selecting a spectral line within the range-Doppler target image signature from a modulation feature on the target which comprises an effective point scatterer;c. providing a range profile for the spectral line;d. obtaining a reference range profile of a reference point scatterer;e. determining a difference between a power at a range shorter than a peak corresponding to the modulation feature in the range profile and a power at a corresponding range of the reference range profile;f. determining whether the difference is above a threshold value; andg. where the difference is not above the threshold value, generating a first control signal arranged to cause provision of the range-Doppler target image signature, and, where the difference is above the threshold value, generating a second control signal arranged to prevent provision of the range-Doppler target image signature. 2. A method as claimed in claim 1, wherein b. comprises: i. identifying one or more spectral lines comprising a signal power peak;ii. generating a range profile for each said spectral line;iii. selecting a said spectral line having a range profile comprising a primary power peak and one or more secondary power peaks, and each said secondary power peak located at a shorter range that the primary power peak having a substantially lower power that the primary power peak. 3. A method as claimed in claim 2, wherein i. comprises: selecting the or each of the identified spectral lines corresponding to a modulation feature not located on a skin of the target. 4. A method as claimed in claim 2, wherein iii. comprises: selecting the spectral line comprising the highest signal power peak and the said range profile. 5. A method as claimed in claim 2, wherein the spectral line is identified as being from a modulation feature comprising an effective point scatterer by: determining a difference between a range width of a primary power peak of a range profile of the spectral line and a range width of a corresponding power peak of the reference range profile;determining whether the difference is above a threshold value; andif the difference is not above the threshold value, identifying the said spectral line as being from a modulation feature comprising an effective point scatterer. 6. A method as claimed in claim 5, wherein the range width comprises: a full width of the power peak at a 3 dB power point of the peak and the threshold value comprises 10 percent of the range width of the power peak of the reference range profile. 7. A method as claimed in claim 1, wherein the spectral line comprises: one of a jet engine modulation spectral line, a rotor chopping line, a propeller chopping line and a reflection from a scanning antenna. 8. A method as claimed in claim 1, wherein the reference range profile comprises: a range profile of a spectral line from a modulation feature of a reference target comprising an effective point scatterer. 9. A method as claimed in claim 1, wherein e. comprises: determining a mean difference between powers at a plurality of range cells at ranges shorter than a peak corresponding to the modulation feature in the range profile and powers at a corresponding plurality of range cells of the reference range profile. 10. A method as claimed in claim 1, wherein in a., generating the range-Doppler target image signature comprises: applying a gain and the method comprises:generating and transmitting a third control signal arranged to change the gain to reduce power of returns in a subsequent range-Doppler target image signature. 11. A method as claimed in claim 10, wherein e. comprises: generating and transmitting a gain re-set signal arranged to re-set the gain to a default value following generation of each RDI signature and the third control signal is transmitted after the gain re-set signal so that a gain variation value is applied following re-setting of the gain. 12. A method as claimed in claim 10, comprising: providing an overdriven reference range profile generated from a reference radar return signal having a power arranged to cause a radar receiver to operate in saturation, and wherein generating the third control signal comprises:determining a difference between a power at a range shorter than a peak corresponding to the modulation feature in the range profile and a power at a corresponding range of an overdriven reference range profile;obtaining a gain value in dependence on the difference; andgenerating and transmitting a third control signal arranged to cause the gain to be changed by a gain variation value before generation of a subsequent range-Doppler target image signature. 13. A method as claimed in claim 1, wherein the range-Doppler target image signature comprises: a high range resolution range-Doppler target image signature. 14. A method of controlling provision of a range-Doppler target image signature of a target, the method comprising: a. receiving a range-Doppler target image signature of a target;b. identifying a spectral line within the range-Doppler target image signature from a modulation feature on the target which comprises an effective point scatterer;c. providing a range profile for a return from the modulation feature;d. obtaining a reference range profile of a reference point scatterer;e. determining a difference between a power at a range shorter than a peak corresponding to the modulation feature in the range profile and a power at a corresponding range of the reference range profile;f. determining whether the difference is above a threshold value; andg. where the difference is not above the threshold value, generating a first control signal arranged to cause provision of the range-Doppler target image signature, and, where the difference is above the threshold value, generating a second control signal arranged to prevent provision of the range-Doppler target image signature. 15. A method as claimed in claim 14, wherein b. comprises: i. identifying one or more spectral lines comprising a signal power peak;ii. generating a range profile for each said spectral line;iii. selecting a said spectral line having a range profile comprising a primary power peak and one or more secondary power peaks, and each said secondary power peak located at a shorter range that the primary power peak having a substantially lower power that the primary power peak. 16. A method as claimed in claim 15, wherein i. comprises: selecting the or each of the identified spectral lines corresponding to a modulation feature not located on a skin of the target. 17. A method as claimed in claim 15, wherein iii. comprises: selecting the spectral line comprising a highest signal power peak and the said range profile. 18. A method as claimed in claim 15, wherein the spectral line is identified as being from a modulation feature comprising an effective point scatterer by: determining a difference between a range width of a primary power peak of a range profile of the spectral line and a range width of a corresponding power peak of the reference range profile;determining whether the difference is above a threshold value; andif the difference is not above the threshold value, identifying the said spectral line as being from a modulation feature comprising an effective point scatterer. 19. A method as claimed in claim 18, wherein the range width comprises: a full width of the power peak at a 3 dB power point of the peak and the threshold value comprises 10 percent of the range width of the power peak of the reference range profile. 20. A method as claimed in claim 14, wherein the spectral line comprises one of: a jet engine modulation spectral line, a rotor chopping line, a propeller chopping line and a reflection from a scanning antenna. 21. A method as claimed in claim 14, wherein the reference range profile comprises: a range profile of a spectral line from a modulation feature of a reference target comprising an effective point scatterer. 22. A method as claimed in claim 14, wherein the range-Doppler target image signature comprises: a high range resolution range-Doppler target image signature. 23. A radar system comprising: receiver apparatus arranged to receive a radar return signal and to generate a range-Doppler target image signature; anda controller, and an associated computer program stored in non-transitory form which will configure the controller to:a. select a spectral line within the range-Doppler target image signature from a modulation feature on the target which comprises an effective point scatterer;b. provide a range profile for the spectral line;c. obtain a reference range profile of a reference point scatterer;d. determine a difference between a power at a range shorter than a peak corresponding to the modulation feature in the range profile and a power at a corresponding range of the reference range profile;e. determine whether the difference is above a threshold value; andf. where the difference is not above the threshold value, generate a first control signal arranged to cause provision of the range-Doppler target image signature, and, where the difference is above the threshold value, generate a second control signal arranged to prevent provision of the range-Doppler target image signature. 24. A radar system as claimed in claim 23, wherein the controller will be configured in b. to: i. identify one or more spectral lines comprising a signal power peak;ii. generate a range profile for each said spectral line;iii. select a said spectral line having a range profile comprising a primary power peak and one or more secondary power peaks, such that each said secondary power peak located at a shorter range that the primary power peak will have a substantially lower power that the primary power peak. 25. A radar system as claimed in claim 24, wherein the controller is configured in i. to: select the or each of the identified spectral lines corresponding to a modulation feature not located on a skin of the target. 26. A radar system as claimed in claim 24, wherein the controller is configured in iii. to: select the spectral line comprising the highest signal power peak and the said range profile. 27. A radar system as claimed in claim 24, wherein the controller is configured to identify the spectral line as being from a modulation feature comprising an effective point scatterer by: determining a difference between a range width of a primary power peak of a range profile of the spectral line and a range width of a corresponding power peak of the reference range profile;determining whether the difference is above a threshold value; andif the difference is not above the threshold value, identifying the said spectral line as being from a modulation feature comprising an effective point scatterer. 28. A radar system as claimed in claim 27, wherein the range width comprises: a full width of the power peak at a 3 dB power point of the peak and the threshold value comprises 10 percent of the range width of the power peak of the reference range profile. 29. A radar system as claimed in claim 23, wherein the controller is configured to: select a spectral line comprising one of a jet engine modulation spectral line, a rotor chopping line, and a reflection from a scanning antenna. 30. A radar system as claimed in claim 23, wherein the reference range profile comprises: a range profile of a spectral line from a modulation feature of a reference target comprising an effective point scatterer. 31. A radar system as claimed in claim 23, wherein the controller is configured in e. to: determine a mean difference between powers at plurality of range cells at ranges shorter than a peak corresponding to the modulation feature in the range profile and powers at a corresponding plurality of range cells of the reference range profile. 32. A radar system as claimed in claim 23, comprising: a signal power control apparatus configured to apply a gain to the range-Doppler target image signature, wherein the controller is configured to generate and transmit a third control signal arranged to change the gain applied by the signal power control apparatus to reduce a power of returns in a subsequent range-Doppler target image signature. 33. A radar system as claimed in claim 32, wherein the controller is configured to: generate a re-set signal arranged to re-set the gain to a default value following generation of each RDI signature, and the controller is configured to transmit the third control signal after transmitting the re-set signal so that a gain variation value is applied following re-setting of the gain. 34. A radar system as claimed in claim 32, wherein the controller is configured to: provide an overdriven reference range profile generated from a reference radar return signal having a power arranged to cause a radar receiver to operate in saturation, and the controller is configured to generate the third control signal by:determining a difference between a power at a range shorter than a peak corresponding to the modulation feature in the range profile and a power at a corresponding range of an overdriven reference range profile;obtaining a gain value in dependence on the difference; andgenerating a third control signal arranged to cause the gain to be changed by a gain variation value before generation of the subsequent range-Doppler target image signature. 35. A radar system as claimed in claim 23, configured for a selected range resolution.