US 4,794,395 A · Passive interferometric imaging receiver system · patentgrep

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Abstract

A passive detection and imaging system employs interferometric and synthetic aperture techniques. A moving platform employs a pair of sensors which receive thermal electromagnetic radiations from an area of interest. The received signals are narrow band filtered by a bank of filters covering an extended bandwidth. Signals from similar narrow bands from different sensors are correlated. The plurality of frequencies and plurality of positions relative to the area of interest due to the platform motion enable generation of an inverse Fourier transform image which is resolvable in both azimuth and range. Separate preferred embodiments operating at microwave frequencies and optical frequencies are disclosed. An achromatic optical interferometric correlation technique is also disclosed.

Claims30

Dependent claims

A passive interferometric imaging receiver comprising:

a pair of sensors disposed on a moving platform along a baseline substantially parallel to the motion of the moving platform, separated by a distance d, each for receiving electromagnetic radiation from an area of interest and generating a received signal proportional to the amplitude and phase of said received electromagnetic radiation;
a pair of filtering means, each filtering means receiving said received signal from a corresponding one of said sensors, each filtering means for generating a plurality of filtered signals corresponding to the portion of said received signal of said corresponding sensor within a set of predetermined narrow bandwidths;
a plurality of correlation means, each correlation means receiving one of said filtered signals from each of said filtering means for a selected one of said narrow bandwidths, each correlation means for generating a correlation signal representing the correlation of said received signals from said pair of sensors over an interval of time T within said selected narrow bandwidth;
a position indicating means for detecting and indicating the position of the moving platform relative to the area of interest;
and
a Fourier imaging means connected to said plurality of correlation means and said position indicating means for generating a Fourier transform of said correlation signals over the intervals of time T at positions indicated by said position indicating means thereby forming an image of the area of interest.

3 more elements

A passive interferometric imaging receiver system comprising:

a moving platform having a generally straight line of motion with regard to an area of interest;
a pair of sensors disposed on said moving platform along a baseline substantially parallel with said line of motion, said senors separated by a distance d, for receiving electromagnetic radiation from the area of interest and generating a received signal proportional to the amplitude and phase of said received electromagnetic radiation;
a pair of filtering means, each filtering means receiving said received signal from a corresponding one of said sensors, each filtering means for generating a plurality of filtered signals corresponding to the portion of said received signal within respective narrow bandwidths;
a plurality of correlation means, each correlation means receiving one of said filtered signals from each of said filtering means for a selected one of said narrow bandwidths, each of said correlation means for generating a correlation signal representing the correlation of said received signals from said pair of sensors over a time interval T within said selected narrow bandwidth;
a position indicating means for detecting and indicating the position of said moving platform relative to the area of interest;
and
a Fourier imaging means connected to said plurality of correlation means and said position indicating means for generating a Fourier transform of said correlation coefficients over the time interval T at positions indicated by said position indicating means thereby forming an image of the area of interest.

4 more elements

A passive interferometric imaging receiver comprising:

a pair of steerable microwave antenna disposed on a moving platform along a baseline parallel to the motion of the moving platform, each for receiving microwave electromagnetic radiation from an area of interest and generating an electrical signal proportional to the amplitude and phase of said received microwave radiation;
a local oscillator means for generating a local oscillator signal having a predetermined frequency;
a pair of heterodyning means, each connected to a corresponding one of said pair of microwave antennas and to said local oscillator means for heterodyning said electrical signal with said local oscillator signal thereby generating a heterodyne signal;
a pair of filter banks, each filter bank connected to a corresponding one of said heterodyning means and having a plurality of narrow bandpass filters, said narrow bandpass filters having pass bands and center frequencies to provide nonoverlapping coverage of a bandwidth B, each of said pair of filter banks receiving said heterodyne signal from said corresponding heterodyning means and generating a plurality of filtered signals, each filtered signal corresponding to the portion of said heterodyne signal within the narrow bandpass of a corresponding narrow bandpass filter;
a plurality of correlation means, each correlation means receiving said filtered signals from corresponding narrow bandwidth filters of said pair of filter banks, each correlation means for generating a correlation signal representing the correlation of said filtered signals over a time interval T within the corresponding narrow bandwidth;
at least one variable delay means disposed between one of said narrow bandpass filters and the corresponding correlation means having a controllable delay for delaying the corresponding filtered signal;
a position indicating means for detecting and indicating the position of the moving platform relative to the area of interest;
a beam steering means connected to said pair of microwave antenna, said at least one variable delay means and said position indicating means for steering the main response of each said microwave antenna to the area of interest and for controlling said delay of said at least one variable delay means for steering the main response of said pair of microwave antenna to the area of interest;
and
a Fourier imaging means connected to said plurality of correlation means and said position indicating means for generating a Fourier transform of said correlation signals over the time intervals T at position indicated by said position indicating means thereby forming an image of the area of interest.

7 more elements

A passive interferometric imaging receiver comprising:

a coherent light source for generating a pair of identical local oscillator light signals having a plurality of predetermined wavelengths;
a pair of beam combining means, each disposed on a corresponding optical axis and receiving one of said local oscillator light signals from said coherent light source, for combining said local oscillator light signal and light received on the corresponding optical axis;
a pair of diffraction gratings, each receiving combined light from a corresponding beam combining means, for dispersing the plurality of wavelengths of said corresponding local oscillator light signal;
a pair of optical collecting means, each receiving the dispersed combined light from a corresponding diffraction grating, for focusing said dispersed combined light at a corresponding focal plane;
a pair of linear array detector means, each disposed at a corresponding focal plane and including a plurality of detectors, each detector for detecting the heterodyne signal between said light received on a corresponding optical axis and one of said dispersed wavelengths of the corresponding local oscillator light signal at said focal plane and generating a signal corresponding t the amplitude and phase of said detected heterodyne signal;
a pair of filter banks, each filter bank connected to a corresponding one of said linear array detector means and having a plurality of narrow bandpass filters, each detector connected to at least one narrow bandpass filter, said narrow bandpass filters having pass bands and center frequencies to provide nonoverlapping coverage of a bandwidth B, each of said narrow bandpass filters receiving said detected heterodyne signal from a corresponding detector and generating a filtered signal corresponding to the portion of said detected heterodyne signal within the narrow bandpass of said narrow bandpass filter;
a plurality of variable delay means, each receiving the filtered signal of a corresponding narrow bandpass filter and having a controllable delay;
a position indicating means for detecting and indicating the position of the moving platform relative to an area of interest;
a beam-steering means connected to said variable delay means and said positon indicating means for controlling said variable delay of said plurality of variable delay means for steering the main response of said interferometric imaging receiver to light received on said pair of optical axes to the area of interest;
a plurality of correlation means, each correlation means receiving signals from a corresponding pair of vriable delay means filter banks, each correlation means for generating a correlation signal representing the correlation of signals received upon said pair of optical axes over a time interval T within a corresponding narrow bandwidth;
and
a Fourier imaging means connected to said plurality of correlation means and said position indicating means for generating a Fourier transform of said correlation signals over the time interval T at positions indicated by said position indicating means thereby forming an image of the area of interest.

9 more elements

A passive interferometric imaging receiver comprising:

a pair of diffraction gratings, each disposed for receiving light from an area of interest along a corresponding optical axis, each having a spatial frequency F, light diffracted from said diffraction gratings crossing and interfering in an interference fringe box;
at least one detecting diffraction grating disposed within said interference fringe box at a position for receiving diffracted light from each of said pair of diffraction gratings and recombining said diffracted light, having a spatial frequency F;
at least one optical system one corresponding to each detecting diffraction grating disposed for receiving said recombined light from said detecting diffraction grating for directing said recombined light to a focal point;
at least one detector means disposed at said focal point of a corresponding optical system for detecting the light received and generating a detection signal corresponding to the intensity of said interferred light;
a position indicating means for detecting and indicating the position of the moving platform relative to the area of interest;
a Fourier imaging means connected to said at least one detecting means and said position indicating means for generating a Fourier transform of said detector signal of said detecting means over time intervals T at positions indicated by said position indicating means at plural frequency bands thereby forming an image of the area of interest.

3 more elements

A passive interferometric imaging receiver comprising:

a plurality of sensors disposed on a moving platform along a baseline substantially parallel to the motion of the moving platform, each sensor for receiving electromagnetic radiation from an area of interest and generating a received signal proportional to the amplitude and phase of said received electromagnetic radiation;
a plurality of filtering means, each filtering means receiving said received signal from a corresponding one of said sensors, each filtering means for generating a plurality of filtered signals corresponding to the portion of said received signal of said corresponding sensor within a set of predetermined narrow bandwidths;
a plurality of correlation means, each correlation means receiving one of said filtered signals from each of a selected pair of filtering means for a selected one of said narrow bandwidths, each correlation means for generating a correlation signal representing the correlation of said received signals from said selected pair of sensors over an interval of time T with said selected narrow bandwidth;
a position indicating means for detecting and indicating the position of the moving platform relative to the area of interest;
a Fourier imaging means connected to said plurality of correlation means and said position indicating means for generating a Fourier transform of said correlation signals over the intervals of time T at positions indicated by said position indicating means thereby forming an image of the area of interest.

2 more elements

Dependencies are inferred from the claim text.