Apparatus for and method of adaptively processing sonar data
First Claim
1. An adaptive normalization processor of a sonar power spectrum for improving the detectability of discrete spectral line data for target detection and classification in a background of broadband noise containing both relatively broad and narrow (with respect to the center frequency of the spectral band) interference ripples due to the reception of broadband signals via multipath propagation, said processor comprising:
- A. an input port for connection to a source of sonar spectral data in a periodically scanned power spectrum format containing both said spectral line data and said broadband background;
B. means to perform a real to complex Fourier transformation of said sonar data in said power spectrum format to form a complex autocorrelation function whose magnitude contains peak(s) at time differences in said scan corresponding to the inverse of the period of the interference ripples in the broadband spectral data;
C. means to compute the magnitudes of said complex autocorrelation function to form a correlation magnitude function;
D. means responsive to said correlation magnitude function to select values of said complex autocorrelation function over time difference interval(s) containing said high amplitude peak(s) while maintaining zero values for all other time difference in said scan to form a gated comples autocorrelation function from which only the broadband spectrum is derived;
E. means to perform the inverse complex to real Fourier transformation of said gated complex autocorrelation function to obtain an estimate of said broadband data in a power spectrum format;
F. means to perform a vector division of said imput sonar data for each scan by said broadband data estimate computed from said scan to normalize said spectral line data in relation to said background for improved detectability; and
G. an output port for application of said normalized electrical sonar data to a visual display.
3 Assignments
0 Petitions
Accused Products
Abstract
The invention discloses an apparatus for and a method of adaptively processing a sonar power spectrum for improving the display of narrowband line structure characteristic of a target in a background of broadband interference which is rippled due to multipath propagation arrival structure. The processor employs a first Fourier transformer to convert the sonar frequency data into a complex correlation format. The autocorrelation is then time difference sampled to separate the broadband ripple interference from the broadband trend interference. The separate time difference samples are then transformed back to their real frequency format to form a broadband ripple estimate and a broadband trend estimate of the interference background. The ripple estimate is subtracted from the sonar signal to remove the ripple component and the resulting difference is normalized by a division by the interference trend estimate. The result is improved detectability of the narrowband lines in the presence of widely varying multipath interference.
-
Citations
11 Claims
-
1. An adaptive normalization processor of a sonar power spectrum for improving the detectability of discrete spectral line data for target detection and classification in a background of broadband noise containing both relatively broad and narrow (with respect to the center frequency of the spectral band) interference ripples due to the reception of broadband signals via multipath propagation, said processor comprising:
-
A. an input port for connection to a source of sonar spectral data in a periodically scanned power spectrum format containing both said spectral line data and said broadband background; B. means to perform a real to complex Fourier transformation of said sonar data in said power spectrum format to form a complex autocorrelation function whose magnitude contains peak(s) at time differences in said scan corresponding to the inverse of the period of the interference ripples in the broadband spectral data; C. means to compute the magnitudes of said complex autocorrelation function to form a correlation magnitude function; D. means responsive to said correlation magnitude function to select values of said complex autocorrelation function over time difference interval(s) containing said high amplitude peak(s) while maintaining zero values for all other time difference in said scan to form a gated comples autocorrelation function from which only the broadband spectrum is derived; E. means to perform the inverse complex to real Fourier transformation of said gated complex autocorrelation function to obtain an estimate of said broadband data in a power spectrum format; F. means to perform a vector division of said imput sonar data for each scan by said broadband data estimate computed from said scan to normalize said spectral line data in relation to said background for improved detectability; and G. an output port for application of said normalized electrical sonar data to a visual display. - View Dependent Claims (2, 3, 4, 5, 6)
-
-
7. A method of adaptively normalizing a sonar power spectrum to improve the detectability of discrete spectral line data for target detection and classification in a background of broadband noise containing both relatively broad and narrow (with respect to the center frequency of the spectral band) interference ripples due to the reception of broadband signals via multipath propagation, said method comprising the steps of:
-
A. providing said sonar electrical data in a periodically scanned power spectrum format, B. performing a real to complex Fourier transformation of said sonar data to form a complex autocorrelation function, C. computing the magnitudes of said complex autocorrelation function to form a correlation magnitude function;
whose magnitude contains peak(s) at time differences in said scan corresponding to broadband data;D. selecting values of said complex autocorrelation function over time difference interval(s) containing said intensity peak(s) while maintaining zero values for all other time differences in said scan to form a gated complex autocorrelation function in which broadband data is selected and spectral line data is rejected, E. performing the inverse complex to real Fourier transformation of said gated complex autocorrelation function to obtain an estimate of said broadband data in a power spectrum format; F. dividing said input power spectrum for each scan by said broadband data estimate computed from said scan to normalize said spectral line data in relation to said background for improved detectability; and G. coupling said normalized electrical sonar data to an output port for application to a visual display. - View Dependent Claims (8, 9, 10, 11)
-
Specification