Abstract: An Atmospheric Turbulence Detector utilizes a sensor to detect noise and extracts infrasound having frequencies below a specified infrasound frequency. A threshold is computed from the detection of infrasound in the vicinity of the sensor prior to the arrival of infrasound from the turbulence and an alarm is given when the infrasound from the turbulence are determined with the utilization of two sensors (6-1A, 6-1B), measuring amplitude differences of the infrasound detected at two seperate locations.

Abstract: A method and apparatus for measuring the parameters of atmospheric turbulent flows utilizes the Doppler shifted frequencies of received radar signals backscattered from sound generated aerodynamically by atmospheric turbulent flows. Doppler frequency bandwidths of the received backscattered signals are used to estimate the atmospheric flow turbulence and the mean frequency within a bandwidth is processed to estimate its radial flow velocity. Total flow velocity and the flow velocity angle with respect to the antenna boresight of the atmospheric turbulent flow may be estimated by estimating the radial flow velocity at two radial positions and processing these radial velocities. Processing of the Doppler data is initiated when the total signal power within the Doppler frequency band exceeds a predetermined power level.

Abstract: A passive target positioning system utilizes three stations positioned on a linear baseline with a central master station positioned predetermined distances from two slave stations. Angle to the target is determined from the time differences of arrival at the master station and each of the slave stations. Range to the target, in one embodiment, is determined from the difference of the two time difference of arrival measurements and the angle-to-target, while in a second embodiment from the time differences of arrival. A scannable antenna with frequency selection capability provides a spatial sector and frequency band selectivity.

Abstract: Clutter reduction is accomplished by dividing the sampling times of received radar signals into blocks containing a plurality of sampling times. The average clutter value in each block is estimated by averaging the signal returns for the sampling times in the block. Block average clutter values are time positioned at a selected sampling time position in a block and a smooth function with continuous first and second derivatives is passed through the average clutter value points. In a preferred embodiment the smooth function is a cubic spline comprising third order polynomial segments between average clutter value points. Clutter values at the sampling points are extracted from the smooth function and respectively subtracted from the received radar signals. A clutter sensor examines the resulting radar signals for clutter distortion and eliminates radar signals that are not substantially clutter free.

Abstract: A method and apparatus for resolving Doppler frequency shift ambiguities in pulse Doppler radar systems provides a radiated signal that is modulated with a periodic waveform having a plurality of pulses within a period, the interpulse intervals between pulses in the period being unequal. Radar target returns are autocorrelated for a plurality of lags, which may include the interpulse intervals and linear combinations thereof. The calculated arguments .theta..sub.Ci of the autocorrelation function are unwrapped by adding 2k.sub..pi., k=0, .+-.1, .+-.2, . . . , to the phase .theta..sub.C1 obtained for the shortest lag T.sub.1 and determining an integer m.sub.k2 from .vertline.(.theta..sub.C2 +2m.sub.k2 .pi.)-(T.sub.2 /T.sub.1).theta..sub.C1 .vertline. <.pi. and then setting .theta..sub.2 =.theta..sub.C2 +2m.sub.k2 .pi.. Phase angles .theta..sub.3, .theta..sub.4, . . . , .theta..sub.m are unwrapped in a similar manner, the integer m.sub.ki being determined from .vertline.(.theta..sub.Ci +2m.sub.ki .pi.)-(T.

Abstract: A spectral moment estimator includes a first processor which processes signals representative of the magnitudes of complex autocorrelation functions of a signal at a plurality lags and provides Doppler spectral width representative signals and the autocorrelation function at zero lag independent of noise. A second processor, processes the complex autocorrelation representative signals, the complex autocorrelation functions phase angles representative signals, and the Doppler spectral width representative signals to provide the mean Doppler frequency of the the signal. The autocorrelation function phase angles are disambiguated and the unambiguous phase angles are least mean square error fitted to a third order odd polynomial, the linear term of which is the mean Doppler frequency of the signal.

Abstract: A portable test system is arranged to enable testing of an aircraft-mounted radar system. Simulated radar returns are transmitted via a test antenna positioned a short distance from an aircraft parked on an airport surface. The varying amplitude of received radar pulses is analyzed as the test antenna is illuminated by the main beam and side lobes of the radar antenna pattern as the radar beam is scanned. By controlling the amplitude of the simulated radar returns in inverse relation to the amplitude of received radar pulses, simulated radar returns inserted off beam center line are interpreted by the radar system as received on the beam center line. Test system transmissions, which may incorporate windshear effect test data, are thus enabled to create simulated effects usable for testing radar system response to a variety of airborne conditions, such as windshear. Test methods are also described.

Abstract: A surveillance sensor for detecting and monitoring aerodynamic conditions in a vicinity of an aircraft landing glide slope utilizes a radar transmitter to illuminate the glide slope. Radar reflections from aircraft induced vortices, clear air turbulence, and glide slope cross winds are received by a monopulse radar system wherein a sum beam doppler spectrum and a difference beam doppler spectrum for the radar returns is determined. The sum and difference beams doppler spectra are processed to determine the aerodynamic conditions in the glide slope vicinity. These aerodynamic conditions are assessed to determine whether aerodynamic hazardous conditions exist in the glide slope region.

Abstract: A weather surveillance apparatus utilizes a set of beams in an elevation angular sector, one beam being offset from the other by a predetermined offset angle. Radar signal returns in each beam are processed to establish an average doppler frequency shift for the signals in the respective beams. An average of the averages and a difference of the averages are determined which are utilized to establish horizontal and vertical wind velocities. These velocities are further processed to determine whether a microburst precursor exists and the location, magnitude, time to impact, and track of any resulting windshear.

Abstract: A microburst precursor detector utilizes a multiplicity of radar beams and samples radar returns, in each beam, from meterological radar signal reflectors and processes the signal returns in a statistical manner to determine average radar reflectivity and to extract doppler signal parameters. These parameters are utilized to determine a second set of parameters; average doppler frequency within each radar beam, doppler spectral spread within each radar beam, and the skewness of the doppler spectrum in each beam. The second set of parameters is processed to establish the existence of a microburst, predicted surface impact, time to impact, wind shear surface location and track, and the magnitude of the wind shear.

Abstract: A spread spectrum radar apparatus wherein a plurality of carrier signals frequency modulated over predetermined time intervals and separated in frequency such that the spectra of the signals do not overlap are sequentially transmitted. Radar returns of this transmission sequence are coupled to a receiver which is frequency band activated in accordance with the transmission sequence and in a manner to minimize radar minimum detection range. Each radar echo is processed through a matched filter for pulse compression, delayed in accordance with the position of its transmitted signal, detected, and non-coherently summed with detections of returns from the same target of other interval transmissions.

Abstract: An optical communication system is disclosed wherein a multiplicity of stations in a linear, random, or grid arrangement are coupled in a party-line type network in which optical signals originated by a master or responding station are relayed from station to station. Coupling between stations may be accomplished by means of optical lenses, the focal regions of which are coupled to electronic equipments that may be remotely located therefrom. This electronic equipment detects received optical signals, regenerates and retransmits these received optical signals, and originates a responding optical signal to the master station when the received optical signal is addressed to the receiving station.