Method for estimating nondirectional wave spectrum from sea echoes of multiple high radar frequencies

Patent metadata

Field	Value
Publication number	US-2022326348-A1
Application number	US-202217711076-A
Country	US
Kind code	A1
Filing date	Apr 1, 2022
Priority date	Apr 1, 2021
Publication date	Oct 13, 2022
Grant date	—

Abstract

The disclosure provides a method for estimating the nondirectional wave spectrum from the sea echoes of multiple HF radar frequencies. The method includes: dividing the radar detection area into a plurality of fan-shaped units at an equal range interval and angle interval according to the distance resolution and the angular resolution of an HF radar; obtaining the Doppler spectrum from the sea echo of a single radar frequency at a fan-shaped unit by performing the first fast Fourier transform (FFT) in distance dimension, the second FFT in Doppler frequency dimension and the digital beamforming; extracting the positive first-order peak and the negative first-order peak from the aforementioned Doppler spectrum by the peak-searching method; and selecting the stronger first-order peak σ R (1) (ω) ; dividing the second-order spectrum on the stronger first-order peak side into an inner second-order spectrum and an outer second-order spectrum.

First claim

What is claimed is:

1 . A method for directly estimating a nondirectional wave spectrum from sea echoes of multiple HF radar frequencies, the method comprising:
(a) dividing a radar detection area into a plurality of fan-shaped units at an equal range interval and angle interval according to a distance resolution and an angular resolution of a multi-frequency HF radar, wherein the multi-frequency HF radar is capable of simultaneously operating at more than one frequency in the HF band; (b) obtaining a Doppler spectrum from a sea echo of a single radar frequency at a fan-shaped unit by performing a first fast Fourier transform (FFT) in distance dimension, a second FFT in Doppler frequency dimension and a digital beamforming in a signal processor unit, extracting a positive first-order peak and a negative first-order peak from the Doppler spectrum by a peak-searching method and selecting a stronger first-order peak σ R (1) (ω) from the positive and negative first-order peaks in a computer processor; (c) dividing a second-order spectrum on a stronger first-order peak side into an inner second-order spectrum and an outer second-order spectrum and separating the outer second-order spectrum on the stronger first-order peak side from the Doppler spectrum in the computer processor according to a Doppler frequency range of the outer second-order spectrum; (d) calculating R f (ω) which is a function of the outer second-order spectrum divided by a first-order peak energy for the stronger side of the Doppler spectrum of the single radar frequency at the fan-shaped unit in the computer processor; (e) calculating A f which is defined as a single-frequency coefficient matrix of the nondirectional wave spectrum by linearizing the outer second-order spectrum on the side of the stronger first-order peak in the computer processor; (f) repeating the above steps (b) to (e), combining the sea echoes of different radar frequencies to construct a matrix R which is a function of the outer second-order spectrum divided by the first-order peak energy for the stronger side of the Doppler spectrum of multiple radar frequencies and merging coefficient matrices of the nondirectional wave spectrum from multiple radar frequencies into a matrix A in the computer processor; and (g) calculating a pseudo-inverse A + of the matrix A by a singular value decomposition and estimating the nondirectional wave spectrum at the fan-shaped unit from the matrix R and the pseudo-inverse A + in the computer processor.

2 . The method of claim 1 , wherein in (b), the Doppler spectrum at the fan-shaped unit is defined as: σ(ω), where ω represents a Doppler frequency generated by the motion of ocean waves to the multi-frequency HF radar; and σ(ω) represents a wave energy distribution at a different value of ω; wherein in (b), the positive first-order peak and negative first-order peak are extracted from the Doppler spectrum at the fan-shaped unit using the peak searching method; the first-order peaks are defined as two peaks in the Doppler spectrum which are roughly symmetrically distributed on both sides of zero frequency; the first-order peaks are generated by the Bragg scattering of the waves of half the radar wavelength that are either advancing directly towards the multi-frequency HF radar or receding directly from the multi-frequency HF radar; wherein (b) comprises:
searching for a point of a maximum amplitude in the Doppler frequency range [0.6ω B ,1.4ω B ] of the Doppler spectrum at the fan-shaped unit as the peak of the positive first-order peak, and recording the Doppler frequency of the peak of the positive first-order peak as ω P+ , wherein ω B =√{square root over (2gk 0 )}, is a Bragg frequency, wherein

k
0

=

2
⁢
π
⁢
f

c

is a radar wavenumber; c is a speed of light; and f is a radar frequency;
searching for a local minimum point inside the peak of the positive first-order peak where the Doppler frequency meets the inequation ω P+ −0.2ω B ≤ω<ω P+ , and denoting the Doppler frequency of the local minimum point inside the peak of the positive first-order peak as ω L+ ;
searching for the local minimum point outside the peak of the positive first-order peak where the Doppler frequency satisfies the inequation ω P+ <ω≤0.2ω B +ω P+ , and recording the Doppler frequency of the local minimum point outside the peak of the positive first-order peak as ω R+ ;
intercepting the Doppler spectrum at the fan-shaped unit with Doppler frequency [ω L+ , ω R+ ] as the positive first-order peak;
searching for the point of the maximum amplitude in the Doppler frequency range [−1.4ω B , −0.6ω B ] of the Doppler spectrum at the fan-shaped unit as the peak of the negative first-order peak, and recording the Doppler frequency of the peak of the negative first-order peak as ω P− ;
searching for the local minimum point inside the peak of the negative first-order peak where the Doppler frequency meets the inequation ω P− <ω≤ω P− +0.2ω B , and denoting the Doppler frequency of the local minimum point inside the peak of the negative first-order peak as ω L− ;
searching for the local minimum point outside the peak of the negative first-order peak where the Doppler frequency satisfies the inequation ω P− −0.2φ B ≤ω<ω P− , and recording the Doppler frequency of the local minimum point outside the peak of the negative first-order peak as ω R− ;
intercepting the Doppler spectrum at the fan-shaped unit with Doppler frequency [ω R− , ω L− ] as the negative first-order peak; and
comparing the amplitude of the peak of the positive first-order peak with that of the negative first-order peak, and selecting the first-order peak with a larger amplitude of the peak point as the stronger first-order peak σ R (1) (ω).

3 . The method of claim 1 , wherein in (c), the second-order spectrum originated from the second-order scattering of ocean waves and radar waves is a continuum with lower amplitude than the first-order peaks and distributed around the first-order peaks; wherein (c) comprises the steps of:
(1) dividing the second-order spectrum on the stronger first-order peak side into an inner second-order spectrum and an outer second-order spectrum; the Doppler frequency range of the outer second-order spectrum on the stronger first-order peak side is given as

{

ω

c
+

<
ω
≤

1.4

ω
B

,

when
⁢

σ
R

(
1
)

Assignees

• Univ Wuhan

Inventors

• Zhao Chen
• Deng Min
• Chen Zezong
• Ding Fan
• Li Jian

Classifications

• G01S7/354 Primary

  Extracting wanted echo-signals (Doppler systems G01S13/50) · CPC title

• G01S7/41 Primary

  using analysis of echo signal for target characterisation; Target signature; Target cross-section · CPC title

• G01S13/88

  Radar or analogous systems specially adapted for specific applications (electromagnetic prospecting or detecting of objects, e.g. near-field detection, G01V3/00) · CPC title

• G01S7/356

  involving particularities of FFT processing · CPC title

• Y02A90/10

  Information and communication technologies [ICT] supporting adaptation to climate change, e.g. for weather forecasting or climate simulation · CPC title