Abstract: An airport runway incursion warning system for monitoring air and ground traffic at an airport. The system is optimally used with an aircraft that has an electronic tag or interrogation system that stores identification information regarding the aircraft, and an RF transponder for receiving interrogation signals and for transmitting the identification information in response thereto. A radar system comprises a plurality of radar sensor units disposed at predetermined installation sites adjacent to a runway. Each radar sensor unit typically has an interface processor and telemetry electronics for communication, although hard-wired communication paths may be used. An RF/telemetry interface is provided for communicating with the radar sensor units when the interface processor and telemetry electronics are used. The RF/telemetry interface is also used to transmit the interrogation signals to the aircraft and receive the identification information therefrom.

Abstract: A radar system and method employing a radar with an electronically scanned antenna array for estimating range and range rate to a target using angle cueing only. The radar transmits radar pulses at the target and searches the projection of the line-of-sight to the target on the ground for ground-bounce returns associated with each transmitted pulse. A processor coupled to the radar and processes the ground-bounce returns to determine an angle corresponding to the maximum reflected multipath ground-bounce return when the antenna array scans the ground. The angle data derived from processing the multipath ground-bounce returns permits computation of the range to and range rate of the target.

Abstract: Systems and methods for measuring RCS patterns of large targets in a compact target range having limited size. The present invention utilizes a compact range whose sweet spot (corresponding to the imaged area of the target) is much smaller than the target size. Inverse synthetic array radar (ISAR) images of successive sections of the target are registered to form a composite image of the whole target. The image is then Fourier transformed to generate an RCS value of the full target. This procedure is repeated for successive measurement angles, an RCS versus .theta. plot is generated corresponding to the RCS pattern of the target. The multiple images may be generated by translating the target and computing RCS plots of the target by combining the multiple images produced during translation, or generating the the multiple images by moving feeds or using multiple feeds of the ISAR system.

Abstract: Apparatus and methods for estimating the cross-range scale factor for a displayed inverse synthetic aperture radar image using received image data. The image data is first converted into a polar format. The image data is then processed by a two-dimensional Fourier transform filter to produce a plurality of image entropy estimates. The best image entropy estimate is selected, and then a cross-range scale factor is computed from the data associated with this estimate. This cross-range scale factor is then displayed on a display, from which an operator can accurately determine the size of target objects imaged by the radar. This, in turn provides for identification of the target objects. More specifically, by using polar-format processing, and by selecting the best image obtained for assumed values of rotation rate of a target object, an accurate estimate of the cross-range scale factor is obtained.

Abstract: 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.

Abstract: 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.

Abstract: 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.

Abstract: 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.

Abstract: 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.

Abstract: 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.