Abstract: The present invention is directed to a space-borne altimetry apparatus having a first receiving antenna, pointing to outer space, for receiving at least one signal emitted by a remote satellite emitter via a direct path; a second receiving antenna, pointing to the Earth, for receiving said signal via an indirect path including a reflection from the Earth surface; and a signal processing means for computing a distance of the apparatus from a specular reflection point of the signal on the Earth surface by cross-correlating the signals received by said first and second antennas; wherein both the first and second receiving antennas are high-gain steerable antennas; and wherein the apparatus may also include antenna control means for steering at least one receiving lobe of the first antenna toward the remote satellite emitter, and at least one receiving lobe of the second antenna toward a specular reflection point on the Earth surface.

Abstract: A circuit for a display used on an aircraft causes the display to display a composite terrain image. The composite terrain image can be formed from first terrain data from a terrain database and second terrain data from a radar system. A display control circuit can generate a display signal for the composite terrain image. The display signal is received by the display. The composite terrain image can be viewed by a pilot.

Abstract: A radar sensor is described that includes a radar transmitter, a radar receiver configured to receive reflected returns of signals output by the radar transmitter, and a signal processing unit configured to process signals received by the radar receiver. The signal processing unit includes a comparator, a first filter comprising an output coupled to a reference input of the comparator, and a second filter comprising an output coupled to a signal input of the comparator. The first and second filters are configured to receive a common input related to the reflected returns. The first filter is configured to have a time constant such that a rise time of the first filter output is faster than a rise time of the second filter output.

Abstract: A method and processor for resolving a processing radar return data to determine a mechanical angle to a target relative to a radar array having a right antenna, an ambiguous antenna, and a left antenna. An LA linear relationship determining, based upon a characteristic number of LA wraps relative to the mechanical angle. Likewise, determining a RA linear relationship determines a characteristic number of RA wraps and a RL linear relationship determines a characteristic number of RL wraps relative to the mechanical angle. All permutations of LA wraps, RA wraps, and RL wraps are listed, and for each permutation, a truth relationship is determined. A look up table is populated with permutations where the truth relationship is true.

Abstract: An altimetry method comprising: providing a signal receiver (RX) on a first platform (S1) flying above a portion of the Earth surface (ES), for receiving a temporal series of signals emitted by a second flying platform (S2) and scattered by said portion of the Earth surface; and computing altimetry waveforms, indicative of an elevation profile of said portion of the Earth surface, by processing the received signals; characterized in that said step of computing altimetry waveforms comprises: cross-correlating the received signals with a plurality of locally-generated frequency-shifted replicas of the emitted signals; introducing a frequency-dependent temporal shift to the correlation waveforms in order to compensate for range delay curvature; and incoherently summing the temporally shifted correlation waveforms (CXC) corresponding to signals scattered by a same region of the Earth surface at different times during motion of said first platform.

Abstract: An electronic circuit comprises a randomizing bit generator configured to generate a randomizing bit sequence based on a sequence selection input signal. The randomizing bit generator includes a counter operable to provide an individual starting count for the randomizing bit sequence and a parity generator responsive to an output of the counter. The circuit further comprises a pseudo-random number generator responsive to the randomizing bit generator. The pseudo-random number generator is operable to provide at least one pulsed signal based at least in part on the random bit sequence. The electronic circuit is operable to substantially eliminate interference in a series of pulsed signal transmissions comprising the at least one pulsed signal from each of two or more navigation devices, where each of the pulsed signals from each of the navigation devices is separated by an automatically adjustable time interval.

Abstract: A terrain awareness and warning system includes electronics for receiving radar returns and providing terrain and/or obstacle alerts or warnings in response to the radar returns. The electronics receives information from a database and the information is utilized to suppress false alerts or warnings.

Abstract: An electronic circuit comprises a randomizing bit generator configured to generate a randomizing bit sequence based on a sequence selection input signal. The randomizing bit generator includes a counter operable to provide an individual starting count for the randomizing bit sequence and a parity generator responsive to an output of the counter. The circuit further comprises a pseudo-random number generator responsive to the randomizing bit generator. The pseudo-random number generator is operable to provide at least one pulsed signal based at least in part on the random bit sequence. The electronic circuit is operable to substantially eliminate interference in a series of pulsed signal transmissions comprising the at least one pulsed signal from each of two or more navigation devices, where each of the pulsed signals from each of the navigation devices is separated by an automatically adjustable time interval.

Abstract: A radio altimeter having a high level of integrity is presented. The radio altimeter includes a processing path configured to process a return signal received from a receive antenna using a first modulation technique and a monitoring path configured to process the return signal received from the receive antenna using a second modulation technique.

Abstract: A weather radar system coupled to a weather radar antenna, including a receive circuit for receiving radar returns received by the antenna and a processor for summing portions of the radar return data to obtain a null response. The processor adjusts the phase or power of at least one portion of the radar return data using a steering vector or a tuning vector.

Abstract: A method of compensating for component errors within a radar altimeter is described. The method includes periodically switching transmit pulses from a transmit antenna to a programmable delay device, calculating an altitude based on a transmit pulse received from the programmable delay device, comparing the calculated altitude to an expected altitude, the expected altitude based on a pre-set delay through the programmable delay device, and compensating an altitude measured by the radar altimeter, based on transmit pulses output through the transmit antenna, by an error correction amount based on a difference between the calculated altitude and expected altitudes.

Abstract: A navigation system having a radar altimeter is disclosed. The navigation system comprises a signal processing unit and one or more antennas in operative communication with the radar altimeter and the signal processing unit. The system further comprises a forward looking radar communicatively coupled to the radar altimeter. The forward looking radar and the signal processing unit are configured to provide forward looking radar measurements, radar altitude measurements from the radar altimeter, and datalink communications within a single forward looking radar scanning sequence.

Abstract: An antenna for a micro air vehicle (MAV) takes the form of a wrap-around antenna (e.g., wrapped around a portion of the MAV) that selectively emits radio signals in different directions depending on a frequency selected by a radio altimeter in the MAV. The radar altimeter may be a pulsed or a frequency modulated continuous wave (FMCW) radar altimeter. The wrap-around antenna includes groups of radiating elements in which at least each group includes an average height that is different from an average height of an adjacent group. Further, the average height of the group determines which group will emit the signals most efficiently so that a desired sector of space may be covered by the signals emitted from the antenna. In one example, the center frequency of the radar altimeter may be controlled in a deterministic manner to cause the radiating elements to successively cover desired sectors of space.

Abstract: In one aspect, a method of radar altimeter operation including a time dependent gain control is described. The method comprises triggering a Sensitivity Time Control (STC) gain control signal at a pulse repetition frequency (PRF) of a transmit pulse to attenuate interference from at least one of an antenna leakage signal and a signal reflected from equipment. The method also includes shaping the STC gain control signal from no attenuation at a first time, before a transmitter sends the transmit pulse, to a stable maximum attenuation at the time the transmitter sends the transmit pulse, to no attenuation at a second time, after the transmitter sends the transmit pulse. The method also includes matching a bandwidth of an intermediate frequency (IF) amplifier to the pulse width of a transmitted pulse.

Abstract: An aircraft electronics system is provided that includes a radar system, a display, an embedded global positioning/inertial navigation system (EGI) and a processor. The radar system is configured to generate aircraft operational data. The display is configured to display the aircraft operational data. The EGI is configured to generate aircraft behavior components and the processor configured to override the aircraft operation data displayed on the display when at least one of the aircraft behavior components is beyond a defined limit, wherein potentially incorrect aircraft operational data affected by at least one of the aircraft behavior component is not displayed.

Abstract: In one aspect, a method of radar altimeter operation, the altimeter including a high frequency counter coupled to a processor is described. The method comprises providing a continuous wave to the high frequency counter upon receipt of a transmit pulse, counting the cycles of the continuous wave, discontinuing counting of the continuous wave cycles upon receipt of a return pulse, outputting a count from the high frequency counter to the processor, and operating the processor to convert the count to an altitude.

Abstract: In one aspect, a method of radar altimeter operation including a time dependent gain control is described. The method comprises triggering a Sensitivity Time Control (STC) gain control signal at a pulse repetition frequency (PRF) of a transmit pulse to attenuate interference from at least one of an antenna leakage signal and a signal reflected from equipment. The method also includes shaping the STC gain control signal from no attenuation at a first time, before a transmitter sends the transmit pulse, to a stable maximum attenuation at the time the transmitter sends the transmit pulse, to no attenuation at a second time, after the transmitter sends the transmit pulse. The method also includes matching a bandwidth of an intermediate frequency (IF) amplifier to the pulse width of a transmitted pulse.

Abstract: A method of detecting interference noise at a radar altimeter. The method comprises periodically emitting a pulse from the pulsed radar altimeter, periodically detecting a noise level in a noise gate, and determining if the noise level detected during each noise-level-detection period exceeds a noise threshold. The period of emitting the pulse is a pulse repetition interval and the noise gate is offset from other gates in the altimeter. If the noise level detected during a noise-level-detection period is greater than the noise threshold, a counter value is incremented by a selected incremental value for that noise-level-detection period and it is determined if the counter value is greater than a count threshold.

Abstract: Methods and apparatus for determining an altitude with an altimeter is provided. One method includes transmitting a signal having a fixed modulation period towards a ground target and then detecting reflected signals off the ground target. The method then implements a single Fast Fourier Transform (FFT) on the detected signals for each modulation period that computes all possible altitudes in real time. A short history of the real time altitude calculations is collected and then the altitude based on the short history of the real time altitude calculations is determined.

Abstract: A method for compensating for range gate slide with respect to received returns within a radar altimeter is described. The method includes adjusting the amount of overlap between a range gate pulse and a radar return signal until an altitude output by the radar altimeter is within a desired tolerance, and incrementally increasing an amount of attenuation within the receiver circuit of the radar altimeter until the radar altimeter breaks track with the radar return signal. the method also includes recording a signal strength and altitude output at each increment of attenuation, determining an altitude error for each altitude output, and fitting the signal strength data against the altitude error using a plurality of variable length line segments.

Abstract: A method for correcting bias in altimetry data for ascending satellite tracks and descending satellite tracks. For satellites operating in tandem, calculate ascending track bias between the height measurement made by the first and the second satellites for the ascending tracks in a region, calculate an ascending bias correction by least squares fitting a polynomial to the bias as a function of significant wave height for the ascending tracks, and apply a portion of the ascending track bias to the sea surface height measurements. The correction can be calculated based on only one track and its crossover points. Another embodiment uses data from only one satellite, estimates the sea state bias at the crossover points separately for the ascending and descending tracks, and apportions a percentage of the difference at the crossover points to the tracks based on minimizing the rms differences between the ascending and descending tracks.

Abstract: A method of detecting interference noise at a radar altimeter. The method comprises periodically emitting a pulse from the pulsed radar altimeter, periodically detecting a noise level in a noise gate, and determining if the noise level detected during each noise-level-detection period exceeds a noise threshold. The period of emitting the pulse is a pulse repetition interval and the noise gate is offset from other gates in the altimeter. If the noise level detected during a noise-level-detection period is greater than the noise threshold, a counter value is incremented by a selected incremental value for that noise-level-detection period and it is determined if the counter value is greater than a count threshold.

Abstract: A method to control a track gate and a level gate in an altimeter tracking an altitude of an airborne vehicle comprising emitting signals, directed toward a terrain, from the airborne vehicle, receiving terrain echo signals, positioning the track gate to a selected reference amplitude on the rising edge of the terrain echo signals, positioning the level gate to within a selected range of the peak amplitude level of the terrain echo signals, measuring a change in a location of the peak amplitude between sequentially received terrain echo signals, and varying a separation between the track gate and the level gate based on the measured change in the location of the peak amplitude. The terrain echo signals comprise reflections of the emitted signals from the terrain, and each terrain echo signal has a rising edge and a peak amplitude.

Abstract: An aircraft electronics system is provided that includes a radar system, a display, an embedded global positioning/inertial navigation system (EGI) and a processor. The radar system is configured to generate aircraft operational data. The display is configured to display the aircraft operational data. The EGI is configured to generate aircraft behavior components and the processor configured to override the aircraft operation data displayed on the display when at least one of the aircraft behavior components is beyond a defined limit, wherein potentially incorrect aircraft operational data affected by at least one of the aircraft behavior component is not displayed.

Abstract: A method for calibrating an altimeter is disclosed. The method comprises monitoring signal strength of one or more altitude measurements. Based on the signal strength, the method applies piecewise linear altitude correction to the one or more altitude measurements to generate altitude correction data. The method further determines a goodness-of-fit for the altitude correction data. The altitude correction data maintains a correct altitude measurement in the presence of variable signal strength.

Abstract: In a combined GPS/altimeter device, the calibration and hence the accuracy of barometric altimeter measurements are enhanced with the aid of derived altitudes from a GPS. The device determines the need for calibration and perform the subsequent computations necessary to facilitate the calibration. Furthermore, the device determines a correction quantity that should be applied to barometric altitude readings, thereby allowing the device to be calibrated while in motion. Both of these features ultimately result in a more accurate determination of altitude.

Abstract: A method for compensating for range gate slide with respect to received returns within a radar altimeter is described. The method includes adjusting the amount of overlap between a range gate pulse and a radar return signal until an altitude output by the radar altimeter is within a desired tolerance, and incrementally increasing an amount of attenuation within the receiver circuit of the radar altimeter until the radar altimeter breaks track with the radar return signal. the method also includes recording a signal strength and altitude output at each increment of attenuation, determining an altitude error for each altitude output, and fitting the signal strength data against the altitude error using a plurality of variable length line segments.

Abstract: A method to compensate for variances in signal path delays for a plurality of radar return processing channels is described. The method comprises providing a signal in the signal path between an antenna and a corresponding receiver of each radar return processing channel, receiving a reflection of the provided signal from each antenna at the corresponding receiver, measuring phase variances between the reflected signals processed by each receiver, and adjusting compensation algorithms for each radar return processing channel based on the measured phase variances.

Abstract: A positioning system for tracking the location of a first responder emergency worker. The system includes mobile enabler units and a personnel badge having a ranging transponder. Two enabler units can use two-way ranging signals, a prescribed turn around time and differential altitude for automatically tracking the location of the badge.

Abstract: A method to control a track gate and a level gate in an altimeter tracking an altitude of an airborne vehicle comprising emitting signals, directed toward a terrain, from the airborne vehicle, receiving terrain echo signals, positioning the track gate to a selected reference amplitude on the rising edge of the terrain echo signals, positioning the level gate to within a selected range of the peak amplitude level of the terrain echo signals, measuring a change in a location of the peak amplitude between sequentially received terrain echo signals, and varying a separation between the track gate and the level gate based on the measured change in the location of the peak amplitude. The terrain echo signals comprise reflections of the emitted signals from the terrain, and each terrain echo signal has a rising edge and a peak amplitude.

Abstract: The invention discloses a device for using radar signals to measure the vertical distance (h) to a surface, comprising a first transmitter and a first transmitting antenna for transmitting radar signals, and a first receiver and a first receiving antenna for receiving radar signals. The device additionally comprises a second receiving antenna and a second receiver, the second receiving antenna being arranged at a first predetermined horizontal distance (?x) from the first receiving antenna, the device also being equipped with means for using signals which have been transmitted from the first transmitting antenna and received at the first and second receiving antennas to calculate the vertical distance to the surface. Suitably, the first and second receivers are one and the same physical unit, to which both the first and the second receiving antennas are coupled.

Abstract: A radar sensor is described that includes a radar transmitter, a radar receiver configured to receive reflected returns of signals output by the radar transmitter, and a signal processing unit configured to process signals received by the radar receiver. The signal processing unit includes a comparator, a first filter comprising an output coupled to a reference input of the comparator, and a second filter comprising an output coupled to a signal input of the comparator. The first and second filters are configured to receive a common input related to the reflected returns. The first filter is configured to have a time constant such that a rise time of the first filter output is faster than a rise time of the second filter output.

Abstract: A method for determining a mechanical angle to a radar target utilizing a multiple antenna radar altimeter is described. The method comprises receiving radar return signals at the multiple antennas, populating an ambiguity resolution matrix with the electrical phase angle computations, selecting a mechanical angle from the ambiguity resolution matrix that results in a least amount of variance from the electrical phase angle computations, and using at least one other variance calculation to determine a quality associated with the selected mechanical angle.

Abstract: A system and method for determining a position of a target within an acceptable tolerance using an iterative approach. A airborne or space-based measuring device is used to measure an estimated position of the target. The information from the measuring device is used in conjunction with either live captured or stored topography, or the like, information relating to the surface of the planet proximate the target to iteratively determine the actual position of the target.

Abstract: A method for determining the height HT of a target above a surface, the method comprising the steps of determining a distance R from a source to a target, determining a distance L representative of a distance traveled by a signal from the target that is reflected by the surface to the source, determining a height H of the source above the surface, and determining the height HT of the target using the equation: H T = ( L 2 - R 2 ) 4 ? H Associated target height errors that result from input errors can also be determined using the equation.

Abstract: A continuous wave ranging system, comprising a modulator 2 for modulating an r.f. carrier wave in accordance with a pseudo random code, a transmitting antenna 5 for radiating the modulated signal towards a target, a receiving antenna 6 and receiver 7 for detecting the signal reflected back from the target, a correlator 8 for correlating the reflected signal with the transmitted code with a selected phase shift corresponding to the current range gate to be tested, whereby the range of the target from the system may be determined, a store 12 containing a plurality of different pseudo random codes, and selector means 13 arranged to supply to the modulator 2 and to the correlator 8 a code from the store 12 which code does not produce a breakthrough sidelobe in at least the next range gate or gates to be tested.

Abstract: This invention is directed to a 3-dimensional imaging lidar, which utilizes modest power kHz rate lasers, array detectors, photon-counting multi-channel timing receivers, and dual wedge optical scanners with transmitter point-ahead correction to provide contiguous high spatial resolution mapping of surface features including ground, water, man-made objects, vegetation and submerged surfaces from an aircraft or a spacecraft.

Abstract: A method for maintaining a position of a hovering vehicle that incorporates a radar altimeter is described. The method includes receiving signals at the radar altimeter based on a change of horizontal direction, operating the radar altimeter to generate a Doppler frequency spectrum based on the received signals, and determining a change in vehicle direction and velocity which will reduce a width of the Doppler frequency spectrum of the received signals. A radar altimeter which generates the Doppler frequency spectrum is also described.

Abstract: A method is disclosed for evaluating the terrain surrounding a radar site. The method comprises to calculate the radar horizon around a radar site from stored terrain elevation information. The information obtained can be used for controlling the scanning profile of the radar, by letting the radar scan above the calculated horizon, and thus avoiding transmitting into the terrain.

Abstract: The present invention provides a radar altimeter system with a closed loop modulation for generating more accurate radar altimeter values. The system includes an antenna, a circulator, a receiver, and a transmitter. The circulator receives or sends a radar signal from/to the antenna. The receiver receives the received radar signal via the circulator. The transmitter generates a radar signal and includes a phase-locked loop circuit for generating the radar signal based on a pre-defined phase signal. The transmitter includes a direct digital synthesizer that generates the phase signal based on a pre-defined clock signal and a control signal. The system includes a digital signal processor and a tail strike warning processor that determine position of a tail of the aircraft relative to ground and present an alert if a warning condition exists based on the determined position of the tail of the aircraft and a predefined threshold.

Abstract: A synthetic aperture radar system uses RF bandwidth and Doppler beam sharpening principles to develop fine altitude and along-track resolutions. To achieve accurate cross-track position measurements the system and method exploit a combination of modes based on a novel antenna pattern combination. The unique arrangement of the antenna patterns allows the radar to process terrain elevation measurements in three independent modes, namely, time-delay response (TDR), amplitude monopulse (AM) and phase monopulse (PM). The additional modes address the interfering scatter problem and the calibration issues required for practical and cost effective operation. The approach also maximizes the number of terrain measurements made per look, thereby reducing the impact of errors and noise through averaging and “voting” (i.e., the comparison of measurements and discarding of “outliers”).

Abstract: Methods and apparatus are provided for operating a radar system to provide a thunderstorm image to a pilot. The method comprises using one or more radar scans depending upon the aircraft altitude, a single upward tilted scan at or below a datum level of about 15,000±3000 feet wherein a clutter free storm image may be obtained and two scans above the datum level; a first upward tilting scan to determine, clutter free, a storm head perimeter and a second lower tilting scan for the storm body with ground clutter. The perimeter is used to discard return echoes from the second scan that lie outside the perimeter or an expansion thereof and retain those lying on or within the perimeter. The result is presented to the pilot. Optionally, the thunderstorm image is graded from center to edge so as to indicate weaker echo intensity near the edge.

Abstract: A multistatic radar has a radar transmitter for illuminating a target with a radar signal. The target reflects the radar signal to three separate radar receivers, each performing a bistatic range measurement to the target. The three bistatic range measurements are combined in a quadratic equation having two solutions (roots). One solution (root) corresponds to a correct three dimensional target position with respect to the radar transmitter while the other is an incorrect three dimensional target position with respect to the radar transmitter. The incorrect three dimensional target position is identified and eliminated by comparing the three dimensional target position to the transmitter location, and the receiver locations. The incorrect three dimensional target position is also identified by the target altitude exceeding a threshold, typically set above 80,000 feet AGL.

Abstract: An altitude measuring system is described that includes a radar altimeter configured to measure altitude and a digital terrain map database. The database includes data relating to terrain elevation and at least one data parameter relating to an accuracy of the terrain elevation data and the altitude measured by the radar altimeter. The system is configured to weigh an altitude derived from the terrain elevation data and the radar altimeter measurements according to the at least one data parameter.

Abstract: A portable, handheld electronic navigation device includes an altimeter and a GPS unit. An internal memory stores cartographic data, for displaying the cartographic data on a display of the navigation device. Accordingly, the device is capable of displaying cartographic data surrounding a location of the unit as determined by GPS and altitude information as determined by the barometric altimeter and GPS. The device provides an enhancement of the calibration and hence the accuracy of barometric altimeter measurements with the aid of derived altitudes from a GPS. The device is able to determine the need for calibration and perform the subsequent computations necessary to facilitate the calibration. Furthermore, the device is able to determine a correction quantity that should be applied to barometric altitude readings, thereby allowing the device to be calibrated while in motion. Both of these features ultimately result in a more accurate determination of altitude.

Abstract: A method for operating a radar altimeter to perform a zero altitude calibration is described. The method includes determining a difference between an altitude measured by the radar altimeter and a desired altitude indication and upon receiving a zero calibration command, subtracting the difference from an altitude output by the radar altimeter.

Abstract: A unit is described that is configured to control detonation of a munition such that the munition is detonated at a desired altitude. The unit includes a radar transmitter, a radar receiver that includes a radar range gate, and a sequencer. The sequencer is configured to receive a detonation altitude and set the range gate based on the received detonation altitude. The unit is also configured to output a detonation signal when radar return pulses received by the receiver aligned with gate delay pulses from the range gate.

Abstract: An altitude measuring system and method for aircraft is provided. The altitude measuring system includes altitude sensors for providing data to an altitude processing unit. The altitude processing unit spatially averages each output to determine a mean altitude. Pitch and roll are accounted for by correction. A method of determining aircraft altitude from a plurality of altitude sensors includes receiving altitude sensor data from each sensor and spatially averaging the altitude sensor outputs to determine aircraft altitude. A method of estimating the maximum height of an ocean surface includes receiving a plurality of altitude sensor data and determining a mathematical description of the ocean surface from the sensor data. The maximum probable wave height of the ocean surface is estimated from the mathematical description. From the maximum wave height, a cruise altitude may be determined.

Abstract: A radar altimeter for an air vehicle is described. The radar altimeter includes a transmit antenna configured to transmit radar signals toward the ground, a receive antenna configured to receive radar signals reflected from the ground, the receive antenna also receiving signals propagated along a leakage path from the transmit antenna, and a receiver configured to receive signals from the receive antenna. The radar altimeter also includes at least one altitude processing channel configured to receive signals from the receiver to determine an altitude, and an automatic sensitivity-range-control (SRC) channel configured to receive signals from the receiver. The SRC channel is configured to determine an amplitude of the received leakage path signals when an altitude of the radar altimeter is sufficient to separate received signals reflected from the ground from signals received from the leakage path.

Abstract: A method for randomly phase modulating a radar altimeter is described. The method includes momentarily applying a signal from a random noise source to an amplifier, applying an output of the amplifier to a voltage controlled oscillator (VCO), applying an output of the VCO to a transmitter and mixer of the radar altimeter to modulate transmissions of the radar altimeter and to demodulate reflected radar transmissions received by the radar altimeter and holding the output of the amplifier constant from before a radar altimeter transmission until after reception of the reflected radar signals from that transmission by the radar altimeter. The method further includes repeating the applying steps and the holding step.