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Measuring velocity of a target by Doppler shift, using improvements in calculating discrete Fourier transform

  • US 5,177,691 A
  • Filed: 11/30/1990
  • Issued: 01/05/1993
  • Est. Priority Date: 11/30/1990
  • Status: Expired due to Fees
First Claim
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1. A method for determining the velocity of a target located in a medium which method comprises the steps of:

  • generating a transmitter electrical signal of prescribed frequency;

    transmitting into said medium coherent vibratory energy which is directed toward said target, said coherent vibratory energy being of a frequency in fixed relationship with said prescribed frequency, said transmitting being done in recurring transmission pulses of prescribed duration;

    receiving from said medium during intervals between said recurring transmission pulses said transmitted coherent vibratory energy after its interaction with said target;

    converting to a receiver electrical signal said received coherent vibratory energy;

    processing said receiver electrical signal to obtain a digital demodulated electrical signal indicative of the phase and frequency differences between said transmitter electrical signal and said receiver electrical signal;

    digitally filtering said digital demodulated electrical signal on a recursive basis to separate it into a plurality k in number of complex digital spectral components with a discrete Fourier transform procedure, said k complex digital spectral components having respective consecutive ordinal numbers selected from the consecutive ordinal numbers zeroeth through (N-1)th, N being a positive integer at least two, said step of digitally filtering being repeated on a recursive basis and comprises for each digital spectral component the respective substeps of;

    combining each sample of said demodulated electrical signal with a complex sample of a respective other signal to generate a complex sample of said digital spectral component of the discrete Fourier transform; and

    multiplying said complex sample of said spectral component by a fraction less than one of an Nth root of unity, to generate the next complex sample of said other signal;

    squaring an absolute value of each complex sample of said complex digital spectral components to generate digital electric signals descriptive of the amplitudes of the power spectrum of the interaction of said vibratory energy with said target;

    performing a comparative analysis of said digital electric signals descriptive of the amplitudes of the power spectrum of the interaction of said vibratory energy with said target; and

    calculating the velocity of said target from the results of said comparative analysis.

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