Dual-frequency, remote ocean-wave spectrometer

• US 4,054,879 A
• Filed: 11/19/1976
• Issued: 10/18/1977
• Est. Priority Date: 11/19/1976
• Status: Expired due to Term

• Current Assignee: the united states of america as represented by the secretary of the navy
• Original Assignee: the united states of america as represented by the secretary of the navy
• Inventors: Wright, John W., Schuler, Dale L., Plant, William J.
• Primary Examiner(s): Tubbesing, T.H.
• Application Number:
  US05/743,372
• Time in Patent Office: 333 Days
• Field of Search: 343/5 SA, 343/5 W
• US Class Current: 342/192
• CPC Class Codes: G01S 7/415 Identification of targets based on measurements of movement associated with the target

Abstract

A coherent, dual-frequency, ocean wave spectrometer radar system for measuring the characteristics of ocean surface gravity waves includes: a transmitter for transmitting a pair of closely spaced, coherently related, microwave frequencies; a receiver for receiving and separating the radar-return signals of the dual-frequency channels; a frequency shifter for offsetting the doppler spectrum of each radar return signal; and a multiplier for multiplying the radar-return signals of the dual-frequency channels to obtain a Bragg resonance condition indicating the presence of a particular gravity wave frequency on the ocean surface.

Claims

1. An ocean-wave spectrometer radar system comprising:

transmitter means, having closely spaced, coherently related, dual-frequency channels, for generating a first local-oscillator frequency and for transmitting a pair of closely spaced microwave frequencies;

coherent receiver means for receiving and separating the radar returns of said transmitter dual-frequency channels;

frequency-shifter means connected to said transmitter means and said receiver means for shifting the frequency of said first local-oscillator frequency; and

multiplier means receiving said separated radar returns from said receiver and multiplying said separated radar returns to obtain a Bragg resonance condition.

2. The system of claim 1 including a precorrelation filter connected between said coherent receiver means and said multiplier means for passing a narrow band of doppler-shifted radar returns from capillaries bunched near gravity-wave crests.

3. The radar system of claim 2, including spectrum analyzer means receiving the output of said multiplier for Fourier-transforming and averaging said multiplier output to produce a power spectrum.

4. An ocean-wave spectrometer radar system comprising:

trnasmitter means, having closely spaced, coherently related, dual-frequency, transmitter channels and including a microwave signal generator, for transmitting a pair of closely spaced microwave frequencies and generating a first local-oscillator frequency;

coherent receiver means, including phase-matching circuitry, for receiving and separating radar returns from said transmitter dual-frequency channels;

frequency shifter means connected to said microwave signal generator and said phase-matching circuitry, for shifting the frequency of said first local-oscillator frequency; and

multiplier means for receiving said separated radar returns from said receiver and multiplying said separated radar returns.

5. The system of claim 4, including a precorrelation filter connected between said phase-matching circuitry and said multiplier for passing a narrow band of doppler-shifted radar returns from capillaries bunched near gravity-wave crests.

6. The radar system of claim 5, including spectrum analyzer means for receiving the output of said multiplier for averaging and Fourier-transforming said multiplier output to produce a power spectrum.

7. An ocean-wave spectrometer radar system comprising:

transmitter means, having closely and variably spaced, coherently related, dual-transmitter channels and including a microwave signal generator, for transmitting a pair of closely and variably spaced microwave frequencies and generating a first local-oscillator frequency;

coherent receiver means, including phase-matching circuitry, for receiving and separating radar returns from said transmitted dual-frequency channels;

frequency shifter means connected to said microwave signal generator and said phase-matching circuitry for shifting the frequency of said first local-oscillator frequency; and

multiplier means for receiving said separated radar returns from said receiver and multiplying said separated radar returns.

8. The system of claim 7, including a precorrelation filter connected between said phase-matching circuitry and said multiplier for passing a narrow band of doppler-shifted radar returns from capillaries bunched near gravity-wave crests.

9. The system of claim 8, in which said precorrelation filter includes a pair of bandpass filters each receiving a different one of the separated radar returns from said phase-matching circuitry.

10. The system of claim 9, in which said transmitter includes:

modulator means for generating a variable modulating frequency;

double balanced mixer means, receiving the output of said microwave frequency generator and said modulating frequency, for generating a pair of variably and closely spaced transmitter frequencies and suppressing said microwave frequency.

11. The system of claim 10, in which said phase-matching circuitry includes:

single sideband generator means receiving said radar returns and said first local oscillator frequency, for producing a first intermediate frequency in phase with said radar returns and another first intermediate frequency 90°

out of phase with said radar returns;

quadrature hybrid generator means, receiving a second local-oscillator signal from said modulator for providing a local oscillator output in phase and another 90°

out of phase with said second local-oscillator signal;

a pair of balanced mixers, one said balanced mixer receiving the in-phase frequencies from said single sideband generator means and said quadrature hybrid means, and the second said balanced mixer receiving the 90°

phase-shifted frequencies from said single sideband generator means and said quadrature hybrid means, for generating one second intermediate frequency in-phase with and one second intermediate frequency phase shifted by 90°

from said in-phase frequencies;

a sum amplifier receiving outputs from each of said pair of balanced mixers, for generating the detected radar returns from one of said frequency channels;

a difference amplifier receiving outputs from each of said pair of balanced mixers, for generating the detected radar returns from the second of said frequency channels.

12. A method for determining the spectrum of capillary wave modulation patterns induced by ocean gravity waves comprising the steps of:

transmitting a pair of closely and variably spaced microwave frequencies;

generating a first local-oscillator frequency related to said transmitted frequencies;

shifting said first local-oscillator frequency;

coherently detecting radar returns of said pair of transmitted frequencies and utilizing said first localoscillator frequency in said coherent detection; and

multiplying said coherently detected radar returns of both frequency channels to obtain a Bragg resonance.