Imaging methods and apparatus using model-based array signal processing
First Claim
1. A method for imaging a region, the method comprising the steps of:
- (a) transmitting a pulse toward the region;
(b) at a receiver transducer array comprising a plurality of N elements detecting a signal scattered from the region to yield a multi-channel scattering signal;
(c) obtaining L snapshots, where L is an integer with L≧
1, by sampling the scattering signal at one or more instants after transmitting the pulse to yield a plurality of complex samples;
(d) in a processing device, processing the plurality of complex samples to obtain image data comprising angles of arrival from M principal scattering components, where M is an integer, with 1≦
M≦
N-1, by the steps of;
(i) constructing a sample matrix SL,M,N from the complex samples;
(ii) from the sample matrix computing a null-space vector w comprising a plurality of entries;
(iii) computing a plurality of roots of a polynomial formed from the entries of the null-space vector;
(iv) from the roots of the polynomial computing angles of arrival for M principal scattering components; and
,(v) storing the angles of arrival as image data.
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Abstract
An apparatus and method for imaging uses a transducer array which receives a scattered signal from a region of interest. The method analyses the scattered signal on the basis of a model which assumes several independent point scatterers at each range. The method determines the amplitudes and angles of arrival for the several scatterers. The method provides much higher resolution than is possible with conventional beam formed sonar arrays of practical size. The method is capable of resolving features which cannot be resolved by conventional sidescan sonar or interferometric side scan sonar. The method may be used with electromagnetic or acoustic scattering signals.
120 Citations
41 Claims
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1. A method for imaging a region, the method comprising the steps of:
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(a) transmitting a pulse toward the region; (b) at a receiver transducer array comprising a plurality of N elements detecting a signal scattered from the region to yield a multi-channel scattering signal; (c) obtaining L snapshots, where L is an integer with L≧
1, by sampling the scattering signal at one or more instants after transmitting the pulse to yield a plurality of complex samples;(d) in a processing device, processing the plurality of complex samples to obtain image data comprising angles of arrival from M principal scattering components, where M is an integer, with 1≦
M≦
N-1, by the steps of;(i) constructing a sample matrix SL,M,N from the complex samples; (ii) from the sample matrix computing a null-space vector w comprising a plurality of entries; (iii) computing a plurality of roots of a polynomial formed from the entries of the null-space vector; (iv) from the roots of the polynomial computing angles of arrival for M principal scattering components; and
,(v) storing the angles of arrival as image data. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30)
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31. An imaging system comprising:
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(a) a transmit transducer; (b) a pulse generator connected to the transmit transducer; (c) a receive transducer array; (d) a receiver connected to the receive transducer array, the receiver comprising; (i) a multi-channel amplifier for amplifying scattered signals detected by each element of the receive transducer array; and
,(ii) an analog to digital conversion circuit connected to the multi-channel amplifier to sample the amplified scattered signals to produce a series of complex samples; (e) a processor connected to receive the series of complex samples from the analog to digital conversion circuit, the processor performing the following operations for each of a plurality of ranges; (i) select a group of complex samples corresponding to a range; (ii) construct a sample matrix SL,M,N from the group of complex samples; (iii) compute from the sample matrix a null space vector w comprising a plurality of entries; (iv) compute the roots of a polynomial formed from the entries of the null-space vector; (v) compute angles of arrival for one or more scatterers from the roots of the polynomial; (vi) compute amplitudes for the one or more scatterers from the sample matrix and the angles of arrival; and
,(vii) store the range, angles of arrival and amplitudes as image data; and
,(f) a display device driver connected to receive the image data and to display the image data on a display device.
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32. A processing unit for processing scattering signal data received at a multi-channel transducer to yield image data, the processing unit comprising:
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(i) an input for receiving scattering signal data, the scattering signal data representing signals scattered by one or more objects and comprising a plurality of sets of complex samples, the sets detected sequentially at a transducer array, each set comprising a complex sample obtained from each of a plurality of elements in the array, (ii) means for selecting a group of complex samples corresponding to a distance range; (iii) means for constructing a sample matrix SK,M,N from the group of complex samples; (iv) means for computing a null-space vector w comprising a plurality of entries from the sample matrix; (v) means for computing roots of a polynomial formed from the entries of the null-space vector; (vi) means for computing angles of arrival for two or more scatterers from the roots of the polynomial; (vii) means for computing amplitudes for the two or more scatterers from the sample matrix and the angles of arrival; (viii) means for storing the range, angles of arrival and amplitudes as image data and, ix output means for delivering an image signal representing the image data, the image signal, when displayed on a display, graphically depicting the objects.
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33. A computer readable medium containing computer software, the computer software, when run on a computer providing a processing means for:
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(a) constructing a sample matrix SK,M,N from the complex samples; (b) obtaining from the sample matrix a null-space vector w; (c) computing the roots of a polynomial formed from the entries of the null-space vector; (d) computing angles of arrival for two or more scatterers from the roots of the polynomial; (e) computing amplitudes for the two or more scatterers from the sample matrix and the angles of arrival; and
,(f) storing the angles of arrival and amplitudes as image data.
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34. A method for imaging a region, the method comprising the steps of:
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(a) transmitting a pulse toward the region; (b) at a receiver transducer array comprising a plurality of N elements, with N≧
2 detecting a signal scattered from the region to yield a multi-channel scattering signal;(c) obtaining L snapshots, where L is an integer with L≧
1, by sampling the scattering signal at one or more instants after transmitting the pulse to yield a plurality of complex samples; and
,(d) in a computer, processing the plurality of complex samples to obtain image data comprising angles of arrival from M principal scattering components, where M is an integer, with 2≦
M≦
N-1. - View Dependent Claims (35, 36, 37, 38, 39, 40, 41)
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Specification