Method for sea surface high frequency radar cross-section estimation using Dopler spectral properties

Claim 1

A method for estimating the high frequency radar sea surface cross-section comprising the steps of: scattering high frequency Doppler radar signals onto a sea surface and receiving echo returns in response therto; correlating said echo returns over an integration time period to obtain a Doppler spectrum of said sea surface; identifying an approach Bragg spectral line, a recede Bragg spectral line, and a zero Doppler frequency continuum level in said Doppler spectrum; measuring the amplitude difference between said approach and recede Bragg spectral lines in said Doppler spectrum to determine an approach/recede amplitude ratio ρ; comparing said approach and recede Bragg spectral lines in said Doppler spectrum to determine the Bragg spectral line having the maximum amplitude; measuring the amplitude difference between the maximum amplitude Bragg spectral line and said zero Doppler frequency continuum level in said Doppler spectrum to determine a measured Bragg line/continuum amplitude ration ζ M ; and estimating the sea surface radar cross-section σ° (θ) from said measured approach/recede ratio σ and said measured Bragg line/continuum ratio ζ M by: determining an angle θ between the radar bearing used and the sea surface wind/wave direction using said approach/recede ratio ρ; determining a Bragg line/continuum saturated ratio ζ SAT from said angle θ; determining a difference value Δ M between said saturated ratio ζ SAT and said measured ratio ζ M ; correcting said difference value Δ M for the integration time period used to obtain said Doppler spectrum to obtain a corrected difference value Δ; and estimating the sea surface radar cross-section σ° (θ) from said corrected difference value Δ and said approach/recede ratio ρ.

Claim 2

A method for estimating the high frequency radar sea surface cross-section comprising the steps of: scattering high frequency Doppler radar signals onto a sea surface and receiving echo returns in response therto; correlating said echo returns over an integration time period to obtain a Doppler spectrum of said sea surface; identifying an approach Bragg spectral line, a recede Bragg spectral line, and a zero Doppler frequency continuum level in said Doppler spectrum; measuring the amplitude difference between said approach and recede Bragg spectral lines in said Doppler spectrum to determine an approach/recede amplitude ratio ρ; comparing said approach and recede Bragg spectral lines in said Doppler spectrum to determine the Bragg spectral line having the maximum amplitude; measuring the amplitude difference between the maximum amplitude Bragg spectral line and said zero Doppler frequency continuum level in said Doppler spectrum to determine a measured Bragg line/continuum amplitude ration ζ M ; and estimating the sea surface radar cross-section σ° (θ) from said measured approach/recede ratio σ and said measured Bragg line/continuum ratio ζ M by: determining an angle θ between the radar bearing used and the sea surface wind/wave direction using said approach/recede ratio ρ; determining a Bragg line/continuum saturated ratio ζ SAT from said angle θ; determining a difference value Δ M between said saturated ratio ζ SAT and said measured ratio ζ M ; correcting said difference value Δ M for the integration time period used to obtain said Doppler spectrum to obtain a corrected difference value Δ; and estimating the sea surface radar cross-section σ° (θ) from said corrected difference value Δ and said approach/recede ratio ρ.

Claim 6

A method for estimating the high frequency radar sea surface cross-section comprising the steps of: scattering high frequency Doppler radar signals onto a sea surface and receiving echo returns in response thereto; correlating said echo returns over an integration time period to obtain a Doppler spectrum of said sea surface; identifying an approach Bragg spectral line, a recede Bragg spectral line, and a zero Doppler frequency continuum level in said Doppler spectrum; measuring the amplitude difference between said approach and recede Bragg spectral lines in said Doppler spectrum to determine an approach/recede amplitude ratio ρ; comparing said approach and recede Bragg spectral lines in said Doppler spectrum to determine the Bragg spectral line having the maximum amplitude; measuring the amplitude difference between the maximum amplitude Bragg spectral line and said zero Doppler frequency continuum level in said Doppler spectrum to determine a measured Bragg line/continuum amplitude ratio ζ M ; determining an angle θ between the radar bearing used and the sea surface wind/wave direction using said approach/recede ratio ρ; determining a Bragg line/continuum saturated ratio ζ SAT from said angle θ; determining a difference value Δ M between said saturated ratio ζ SAT and said measured ratio ζ M ; correcting said difference value Δ M for the integration time period used to obtain said Doppler spectrum to obtain a corrected difference value Δ; and estimating the sea surface radar cross-section σ° (θ) from said corrected difference value Δ and said approach/recede ratio ρ.

Claim 7

A method for estimating the high frequency radar sea surface cross-section comprising the steps of: scattering high frequency Doppler radar signals onto a sea surface and receiving echo returns in response thereto; correlating said echo returns over an integration time period to obtain a Doppler spectrum of said sea surface; identifying an approach Bragg spectral line, a recede Bragg spectral line, and a zero Doppler frequency continuum level in said Doppler spectrum; measuring the amplitude difference between said approach and recede Bragg spectral lines in said Doppler spectrum to determine an approach/recede amplitude ratio ρ; comparing said approach and recede Bragg spectral lines in said Doppler spectrum to determine the Bragg spectral line having the maximum amplitude; measuring the amplitude difference between the maximum amplitude Bragg spectral line and said zero Doppler frequency continuum level in said Doppler spectrum to determine a measured Bragg line/continuum amplitude ratio ζ M ; determining an angle θ between the radar bearing used and the sea surface wind/wave direction using said approach/recede ratio ρ; determining a Bragg line/continuum saturated ratio ζ SAT from said angle θ; determining a difference value Δ M between said saturated ratio ζ SAT and said measured ratio ζ M ; correcting said difference value Δ M for the integration time period used to obtain said Doppler spectrum to obtain a corrected difference value Δ; and estimating the sea surface radar cross-section σ° (θ) from said corrected difference value Δ and said approach/recede ratio ρ.

Claim 11

A method for estimating the high frequency radar cross-section of a target comprising the steps of: scattering high frequency Doppler radar signals onto a sea surface including a target and receiving echo returns in response thereto; correlating said echo returns over an integration time period to obtain a Doppler spectrum of said echo returns; identifying a target spectral line, an approach Bragg spectral line, a recede spectral line, and a zero Doppler frequency continuum level in said Doppler spectrum; estimating the radar cross-section σ° (θ) of said sea surface; and determining the radar cross-section of said target σ T from said radar sea surface cross-section σ° (θ) wherein said of estimating the radar cross section σ° (θ) of said sea surface comprises the steps of: measuring the amplitude difference between said approach and recede Bragg spectral lines in said Doppler spectrum to determine an approach/recede amplitude ratio ρ; comparing said approach and recede Bragg spectral lines in said Doppler spectrum to determine the Bragg spectral line having the maximum amplitude; measuring the amplitude difference between the maximum amplitude Bragg spectral line and said zero Doppler frequency continuum level in said Doppler spectrum to determine a measured Bragg line/continuum amplitude ratio ζ m ; determining an angle θ between the radar bearing used and the sea surface wind/wave direction using said approach/recede ratio ρ; determining a Bragg line/continuum saturated ratio ζ SAT from said angle θ; determining a difference value Δ M between said saturated ratio ζ SAT and said measured ratio ζ M ; correcting said difference value Δ M for the integration time period used to obtain said Doppler spectrum to obtain a corrected difference value Δ; and estimating the sea surface radar cross-section σ° (θ) from said corrected difference value Δ and said approach/recede ratio ρ.

Claim 12

A method for estimating the high frequency radar cross-section of a target comprising the steps of: scattering high frequency Doppler radar signals onto a sea surface including a target and receiving echo returns in response thereto; correlating said echo returns over an integration time period to obtain a Doppler spectrum of said echo returns; identifying a target spectral line, an approach Bragg spectral line, a recede spectral line, and a zero Doppler frequency continuum level in said Doppler spectrum; estimating the radar cross-section σ° (θ) of said sea surface; and determining the radar cross-section of said target σ T from said radar sea surface cross-section σ° (θ) wherein said of estimating the radar cross section σ° (θ) of said sea surface comprises the steps of: measuring the amplitude difference between said approach and recede Bragg spectral lines in said Doppler spectrum to determine an approach/recede amplitude ratio ρ; comparing said approach and recede Bragg spectral lines in said Doppler spectrum to determine the Bragg spectral line having the maximum amplitude; measuring the amplitude difference between the maximum amplitude Bragg spectral line and said zero Doppler frequency continuum level in said Doppler spectrum to determine a measured Bragg line/continuum amplitude ratio ζ m ; determining an angle θ between the radar bearing used and the sea surface wind/wave direction using said approach/recede ratio ρ; determining a Bragg line/continuum saturated ratio ζ SAT from said angle θ; determining a difference value Δ M between said saturated ratio ζ SAT and said measured ratio ζ M ; correcting said difference value Δ M for the integration time period used to obtain said Doppler spectrum to obtain a corrected difference value Δ; and estimating the sea surface radar cross-section σ° (θ) from said corrected difference value Δ and said approach/recede ratio ρ.

Claim 16

A method for estimating the high frequency radar cross-section of a target comprising the steps of: scattering high frequency Doppler radar signals onto a sea surface including a target and receiving echo returns in response thereto; correlating said echo returns over an integration time period to obtain a Doppler spectrum of said echo returns; identifying a target spectral line, an approach Bragg spectral line, a recede spectral line, and a zero Doppler frequency continuum level in said Doppler spectrum; estimating the radar cross-section σ° (θ) of said sea surface; and determining the radar cross-section of said target σ T from said radar sea surface cross-section σ° (θ) by: determining the area of the scattering cell illuminated by said scattered Doppler radar signals from the pulse length and beam width of said Doppler radar signals; adding said radar sea surface cross-section σ° (θ) to said area of said scattering cell to determine the sea surface scattering cross-section σ SEA ; comparing said approach and recede Bragg spectral lines in said Doppler spectrum to determine the Bragg spectral line having the maximum amplitude; measuring the amplitude difference β between the maximum amplitude Bragg spectral line and the amplitude of said target spectral line; and substracting the amplitude difference β from said sea surface scattering cross-section σ SEA to determine the radar cross-section σ T of said target.

Claim 17

A method for estimating the high frequency radar cross-section of a target comprising the steps of: scattering high frequency Doppler radar signals onto a sea surface including a target and receiving echo returns in response thereto; correlating said echo returns over an integration time period to obtain a Doppler spectrum of said echo returns; identifying a target spectral line, an approach Bragg spectral line, a recede spectral line, and a zero Doppler frequency continuum level in said Doppler spectrum; estimating the radar cross-section σ° (θ) of said sea surface; and determining the radar cross-section of said target σ T from said radar sea surface cross-section σ° (θ) by: determining the area of the scattering cell illuminated by said scattered Doppler radar signals from the pulse length and beam width of said Doppler radar signals; adding said radar sea surface cross-section σ° (θ) to said area of said scattering cell to determine the sea surface scattering cross-section σ SEA ; comparing said approach and recede Bragg spectral lines in said Doppler spectrum to determine the Bragg spectral line having the maximum amplitude; measuring the amplitude difference β between the maximum amplitude Bragg spectral line and the amplitude of said target spectral line; and substracting the amplitude difference β from said sea surface scattering cross-section σ SEA to determine the radar cross-section σ T of said target.