Abstract: A rotationally invariant correlator which correlates an arbitrarily rotated image with a large database of similar stored images. The correlator initially scans the image to produce a two-dimensional array of pixels representative thereof. A plurality of concentric rings of pixel data are then produced from the two-dimensional array of pixels. A Fast Fourier Transform is taken of each ring of pixel data which produces an amplitude spectra of the frequency components of that ring of pixel data, which is then normalized. The normalized amplitude spectra for the image being correlated is then compared with normalized amplitude spectra of similar rings of pixel data for similar images in memory, and any matches are identified. The width of each ring of pixel data is selected to be smaller than the size of the smallest features which are to be resolved, while being sufficiently wide to smooth out extraneous noise.

Abstract: An active noise cancellation device and method for reducing fan blade noise over a broad spatial area. The device comprises a microphone, a band pass filter, and audio amplifier, and a speaker array. The microphone captures the sound produced by the fan and converts it into an electrical signal. This electrical signal is input to the band pass filter which has a center frequency equal to product of fan speed and the number of fan blades which comprise the fan. The band pass filter attenuates any signals other than the primary harmonic sound produced by the rotating fan blades. The filtered signal from the band pass filter is input to the audio amplifier. The audio amplifier conditions the signal for input to the speaker array. Accordingly, each speaker in the array receives and outputs an audio signal of equal amplitude and phase as that produced by the rotating fan blades. The speaker array is mounted on or close to the fan hub in a symmetric pattern commensurate with the fan blade geometry.

Abstract: A passive emitter location system is capable of performing emitter location autonomously from a single airborne observation platform and includes a bearing measurement system, a system for measuring doppler induced frequency shifts, and means for estimating the emitter location based on non-simultaneous measurement of the bearing and frequency using extended Kalman filters preferably initialized by a single measurement delayed initialization procedure.

Abstract: In a method of recognizing a radar target object type, target range, heading and speed information are determined. A plurality of RCS for different targets of interest as a function of frequency and aspect angle are stored. Motion information of a platform on which a radar system is carried is determined. The target range, heading and speed information and the motion information of the platform with stored RCS, are processed, and what the observed radar pulse echo should be over the operational frequency band is predicted therefrom. Predicted information is compared with the measured pulse echoes to determine which target is present.

Abstract: A bank of matched filters are employed to impose on a transmitted pulse, as well as the optimum matched filter receiver response, exact amplitude and phase modulations necessary to maximize the likelihood of accurate target identification. This is accomplished by subjecting the output of each matched filter (corresponding to a target signature) to a threshold level detector to eliminate identification outputs caused solely by noise. The outputs from the threshold device represents the target identification from each matched filter. Since each matched filter corresponds to a particular target, the highest output identification signal will indicate the presence of a corresponding target.

Abstract: The signal-to-noise ratio of a received radar echo is maximized by maximizing the received energy E of the echo. The energy E is maximized when the transmitted waveform s(t) is chosen so that ##EQU1## is maximized, where y(t) is the echo signal echoing from the target.

Abstract: A pulse compression modified OMIR waveform s.sub.N (t) is obtained by computing the OMIR eigenfunctions .phi..sub.i, i=1, 2, . . . , .infin., for an autocorrelation function of the expected target impulse response, specifying a waveform c(t) having a desired pulse compression characteristic, and generating expansion terms ##EQU1## for various expansion indices N, until a desired waveform is obtained. The expansion coefficients c.sub.

Abstract: An optimized theoretical approach to the design of a waveform for a matched illumination-reception radar system incorporates radar cross section codes along with detailed target geometry and system constrains to maximize the signal energy of a received echo. An Eigensystem is used to generate a family of solutions, one of which is chosen based upon system constraints to optimize the waveform.