Ultra wideband ground penetrating radar imaging of heterogeneous solids
First Claim
1. A linear array imaging radar system, comprising:
- a linear array of radar transceivers connected to provide a plurality of radar echo samples taken at a variety of delay times, and thus depths into an imaged solid, for each of a series of radar pulse transmission from each radar transceiver;
a position determining system connected to the linear array of radar transceivers and a multiplexer for them that provides an x,y position over a surface of said imaged solid for each group of samples measured for a volume from said surface, wherein the radar transmitter and receiver are moved about said surface to collect such groups of measurements from a variety of x,y positions, and wherein a plurality of return signal amplitudes represent the relative reflectivity of objects within said volume and the delay in receiving each signal echo represents the depth at which an object lays in said volume and the propagation speeds of the intervening material layers; and
means for successively backward propagating deeper z-planes from one layer to the next with an adjustment for variations in the expected propagation velocities of a variety of material layers that lie between adjacent said z-planes, wherein each said z-plane contributes to a tomographic series of slices through said volume that contribute to the visualization of said objects in said volume in three dimensions.
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Accused Products
Abstract
A non-invasive imaging system for analyzing engineered structures comprises pairs of ultra wideband radar transmitters and receivers in a linear array that are connected to a timing mechanism that allows a radar echo sample to be taken at a variety of delay times for each radar pulse transmission. The radar transmitters and receivers are coupled to a position determining system that provides the x,y position on a surface for each group of samples measured for a volume from the surface. The radar transmitter and receivers are moved about the surface, e.g., attached to the bumper of a truck, to collect such groups of measurements from a variety of x,y positions. Return signal amplitudes represent the relative reflectivity of objects within the volume and the delay in receiving each signal echo represents the depth at which the object lays in the volume and the propagation speeds of the intervening material layers. Successively deeper z-planes are backward propagated from one layer to the next with an adjustment for variations in the expected propagation velocities of the material layers that lie between adjacent z-planes.
163 Citations
8 Claims
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1. A linear array imaging radar system, comprising:
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a linear array of radar transceivers connected to provide a plurality of radar echo samples taken at a variety of delay times, and thus depths into an imaged solid, for each of a series of radar pulse transmission from each radar transceiver; a position determining system connected to the linear array of radar transceivers and a multiplexer for them that provides an x,y position over a surface of said imaged solid for each group of samples measured for a volume from said surface, wherein the radar transmitter and receiver are moved about said surface to collect such groups of measurements from a variety of x,y positions, and wherein a plurality of return signal amplitudes represent the relative reflectivity of objects within said volume and the delay in receiving each signal echo represents the depth at which an object lays in said volume and the propagation speeds of the intervening material layers; and means for successively backward propagating deeper z-planes from one layer to the next with an adjustment for variations in the expected propagation velocities of a variety of material layers that lie between adjacent said z-planes, wherein each said z-plane contributes to a tomographic series of slices through said volume that contribute to the visualization of said objects in said volume in three dimensions. - View Dependent Claims (2, 3, 4, 5, 6)
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7. A computer process for extracting tomographic images of a solid from a synthetic aperture radar swept through various points in a plane of observation, the method comprising the steps of:
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collecting data from time delay information (t) provided by a radar signal penetration of a solid from a plane of observation and matching said data with the corresponding positions (x,y) of each observation, wherein said data set may be referred to in the convenient mathematical form as r(x,y,t); placing said data in the frequency domain with a fast Fourier transform (FFT) with respect to time, the result being mathematically expressible as r(x,y,f); scaling the frequency with media propagation velocity to operate with lambda, wherein the result may be expressed conveniently as r(x,y,λ
);fast Fourier transforming with respect to (x,y) to yield a result expressible as R(fx,fy,λ
), where "fx" and "fy" denote spatial frequencies in the x-axis and y-axis;backward-propagating, if this is the first time through, to a next deeper layer by multiplying R(fx,fy,λ
) with a spatial filter H(fx,fy,λ
,Δ
z) to yield image layer I(fx,fy,λ
,zi+1), otherwise multiplying said spatial filter with a previous result, I(fx,fy,λ
,zi), to backward propagate from one deep layer to the next deeper layer, said spatial filter being represented by, ##EQU4## where the factor of two inside the square root accounts for the two-way travel path of the radar pulse, the spatial spectrum of the equivalent source is,
space="preserve" listing-type="equation">S(f.sub.x,f.sub.y,z)=∫
R(f.sub.x,f.sub.y,λ
)H.sup.-1 (f.sub.x,f.sub.y, λ
)dλ
,and where R is the received wavefield and H-1 is the pseudo inverse, the estimate of the source distribution is given by the inverse two-dimensional Fourier transform S, wherein said process of backward propagation begins with a starting z-plane that can be equated to a hologram, and both time and phase information are recorded in such starting z-plane that represent what is illuminating it in radio frequency from deeper z-planes and projecting only to the next deeper z-plane that is then used as a basis for projecting to a still deeper z-plane, and wherein all said projected z-planes are an equal distance Δ
z apart;setting, when still deeper z-planes are to be resolved, a next z-level and adjusting for any expected change in propagation velocity for a new media; integrating or summing said images I(fx,fy,λ
,z) to form an output I(fx,fy,t) and super-positioning all said information collected at various radar frequencies for improving estimates of positions of objects; andinverse Fast Fourier transforming with respect to (fx,fy) to yield a set of final images for said z-planes, expressed as I(x,y,z). - View Dependent Claims (8)
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Specification