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The United States of America As Represented by the Administrator of the

Atul Jain

Robert A Frosch

James C Fletcher

A synthetic aperture radar (10) is employed for .DELTA.k measurement of ocean current from a spacecraft (11) without the need for a narrow beam and long observation times. The SAR signal is compressed (12) to provide image data for different sections of the chirp bandwidth, equivalent to frequencies f.sub.1 (t.sub.a,t), f.sub.2 (t.sub.a,t) . . . f.sub.n (t.sub.a,t), and a common area for the separate image fields is selected (14). The image for the selected area at each frequency is deconvolved (16) to obtain the image signals for the different frequencies (f.sub.1, f.sub.2 . . . f.sub.n) and the same area. A product of pairs of signals is formed (18, 20), Fourier transformed (22) and squared (24). The spectrum thus obtained from different areas for the same pair of frequencies f.sub.jk, f.sub.j+n,k are added (26) to provide an improved signal to noise ratio. The shift of the peak from the center of the spectrum is measured and compared (28) to the expected shift due to the phase velocity of the Bragg scattering wave. Any difference is a measure of current velocity v.sub.c (.DELTA.k).

Method and apparatus for .DELTA.K synthetic aperture radar measurement

A synthetic aperture radar correlation system including a moving diffuser located at the image plane of a radar processor. The output of the moving diffuser is supplied to a lens whose impulse response is at least as wide as that of the overall processing system. A significant reduction in clutter results.

Clutter free synthetic aperture radar correlator

A single-frequency multibeam synthetic aperture radar for large swath imaging is disclosed. Each beam illuminates a separate 'footprint' (i.e., range and azimuth interval). The distinct azimuth intervals for the separate beams produce a distinct Doppler frequency spectrum for each beam. After range correlation of raw data, an optical processor develops image data for the different beams by spatially separating the beams to place each beam of different Doppler frequency spectrum in a different location in the frequency plane as well as the imaging plane of the optical processor. Selection of a beam for imaging may be made in the frequency plane by adjusting the position of an aperture, or in the image plane by adjusting the position of a slit. The raw data may also be processed in digital form in an analogous manner.

Multibeam single frequency synthetic aperture radar processor for

Apparatus for detecting relative motion between a rough reflecting surface and a wave transmitting and receiving system in a plane parallel or perpendicular to the reflecting surface comprised of a transmitter (radar, laser, acoustic, and the like), a receiver having the same or different aperture as the transmitter, and means for detecting the finest interference fringes in the reflected wave pattern. Each fringe detected represents relative motion through a distance, S, that is a function of the maximum dimension, D, of the transmitting aperture. By counting fringes, total relative motion is determined, and by counting fringes for a unit of time, the rate of that motion is determined. For a small transmitting aperture, the distance, S, between fringes is directly related to kD in the parallel plane and to kD/tan .theta., in the normal plane, where .theta. is the angle between a reference axis normal to the reflecting surface and the axis of the receiving aperture, and k is a calibration constant equal to unity when the transmitting and receiving apertures are at the same distance, H, from the reflecting surface. For a large aperture, S.perspectiveto..lambda.H/kD in the parallel plane and S.perspectiveto..lambda.H/kD tan .theta. in the normal plane. In either plane, for the condition of k.perspectiveto.1, the spacing S.perspectiveto..lambda.H/D and S.perspectiveto..lambda.H/D tan .theta. can be measured with a linear scan array so that with .lambda., D and .theta. known, the distance H can be determined.

System for relative motion detection between wave transmitter-receiver

The resolution of an imaging system is greatly enhanced by radiating an object with a plane wave field from a coherent source variable in either frequency, angle or distance from the object, detecting the wave field transmitted through, or reflected from, the object at some point on the image of the object, with or without heterodyne detection, and with or without a lens system. The heterodyne detected output of the detector is processed to obtain the Fourier transform as a function of the variable for a direct measurement of the amplitude and surface height structure of the object within a resolution cell centered at the corresponding point on the object. In the case of no heterodyne detection, only intensity data is obtained for a Fourier spectrum.

Super-resolution imaging system

Apparatus for obtaining significant height information of ocean waves, or peaks of rough terrain utilizing means for compressing the radar signal over different widths of the available chirp or Doppler bandwidths, and means for cross-correlating one of these images with each of the others, where the center frequencies of the images have a spacing .DELTA.f.sub.rO. Upon plotting a fixed (e.g., zero) component of the cross-correlation values R.sup.E (.DELTA.f.sub.rO) as the spacing is increased over some empirically determined range, such as 0 to 1 MHz, the system is calibrated. Thereafter to measure height with the system, a spacing value is selected and a cross-correlation value is determined between two intensity images at a selected frequency spacing, such as 0.1 MHz. The measured height is the slope of the cross-correlation value determined to the spacing value used. Both electronic and optical radar signal data compressors and cross-correlations are disclosed for implementation of the system.

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La Canada, CA, United States of America

Atul Jain