Method for determining a periodic pattern in a line spectrum
First Claim
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1. A method for determining a periodic pattern in a line spectrum comprising the steps of:
- forming an original amplitude line spectrum having a reference line and a plurality of spectral lines which are contiguous to the reference line;
forming a plurality of intervals in the line spectrum by combining a first predetermined number of contiguous spectral lines of the original amplitude line spectrum;
determining a mean value for each respective interval based on an amplitude of each spectral line combined to form the respective interval;
filtering the amplitude of each spectral line of the original amplitude line spectrum with a predetermined factor;
normalizing the filtered amplitude of each spectral line of each respective interval with the associated mean value of the respective interval;
categorizing the normalized amplitudes of the spectral lines into a plurality of overlapping normalized amplitude categories;
determining a periodic complement to each respective spectral line which is a continuation line that is at least contiguous to the reference line for each spectral line and forms a line pair with the respective spectral line;
categorizing each line pair in a relevance category as a function of a predetermined combination of the normalized amplitude categories, each relevance category having a predetermined relevance value range;
determining a relevance value for each line pair;
determining a maximum relevance value for all line pairs associated with one spectral line;
associating the determined maximum relevance value with the spectral line;
forming a residual amplitude line spectrum from spectral lines having an associated relevance value which is greater than a predetermined threshold value;
histogramming the original amplitude line spectrum to determine the number of continuation lines associated with each respective spectral line of the residual amplitude line spectrum;
determining the spectral line having the greatest number of continuation lines from the histogram; and
determining a modulation frequency of the periodic pattern based on the difference in frequency between the spectral line having the greatest number of continuation lines and the reference line.
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Abstract
The invention relates to a method for determining a periodic pattern in an amplitude spectrum, for example, in a Doppler spectrum of a radar echo. A residual spectrum is formed using Fuzzy Set Theory, and the periodic pattern is determined for each residual spectrum by histogramming the original spectrum. The method can be used for identifying aircraft, for example helicopters, that have periodically-moving components, e.g., rotors, that generate a periodic pattern in a Doppler spectrum.
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12 Claims
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1. A method for determining a periodic pattern in a line spectrum comprising the steps of:
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forming an original amplitude line spectrum having a reference line and a plurality of spectral lines which are contiguous to the reference line; forming a plurality of intervals in the line spectrum by combining a first predetermined number of contiguous spectral lines of the original amplitude line spectrum; determining a mean value for each respective interval based on an amplitude of each spectral line combined to form the respective interval; filtering the amplitude of each spectral line of the original amplitude line spectrum with a predetermined factor; normalizing the filtered amplitude of each spectral line of each respective interval with the associated mean value of the respective interval; categorizing the normalized amplitudes of the spectral lines into a plurality of overlapping normalized amplitude categories; determining a periodic complement to each respective spectral line which is a continuation line that is at least contiguous to the reference line for each spectral line and forms a line pair with the respective spectral line; categorizing each line pair in a relevance category as a function of a predetermined combination of the normalized amplitude categories, each relevance category having a predetermined relevance value range; determining a relevance value for each line pair; determining a maximum relevance value for all line pairs associated with one spectral line; associating the determined maximum relevance value with the spectral line; forming a residual amplitude line spectrum from spectral lines having an associated relevance value which is greater than a predetermined threshold value; histogramming the original amplitude line spectrum to determine the number of continuation lines associated with each respective spectral line of the residual amplitude line spectrum; determining the spectral line having the greatest number of continuation lines from the histogram; and determining a modulation frequency of the periodic pattern based on the difference in frequency between the spectral line having the greatest number of continuation lines and the reference line. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12)
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Specification