Abstract: A method for operating a wireless receiver includes receiving wireless signals from a transmitter at a first antenna and a second antenna. The wireless signals include a signal carrier and one or more data symbols modulated onto the signal carrier. The one or more data symbols in the wireless signal are decoded to determine a symbol phase contribution. The phase of the wireless signals at the first antenna and the second antenna during one or more symbol periods is estimated to provide a first set of phase measurements and a second set of phase measurements, respectively. The symbol phase contribution is removed from the first set of phase measurements and the second set of phase measurements to provide a first corrected set of phase measurements and a second corrected set of phase measurements, respectively, which are used to estimate an angle of arrival of the wireless signals.

Abstract: Determining where to place atmospheric sensors that provide measurements of pressure used to estimate an altitude of a mobile device in an environment. Generally, systems and methods determine where atmospheric sensors can be placed relative to each other in order to achieve a required level of accuracy when an altitude of a mobile device is estimated using pressure measurements from the atmospheric sensors in the network. Particular systems and methods determine a maximum distance for separating adjacent atmospheric sensors, or otherwise determine where to place atmospheric sensors relative to each other based on expected pressure distribution of an environment.

Abstract: A method of increasing reliability of a wireless radio includes: creating a first waveform at a first center frequency of an encoded data stream using a first wireless radio; creating a second waveform at a second center frequency of the encoded data stream using the first wireless radio; combining the first waveform and the second waveform into a composite waveform with redundant data streams at different center frequencies using the first wireless radio; wirelessly transmitting the composite waveform using the first wireless radio; wirelessly receiving the composite waveform; filtering the received composite waveform using a first filter band; digitizing the received composite waveform using the second wireless radio; demodulating the digitized composite waveform into a first data stream and a second data stream with the second wireless radio; and creating a third data stream representative of the encoded data stream.

Abstract: Methods and systems are presented for providing a combined barometric value. In some embodiments, the method includes obtaining, at the serving fixed local transceiver, barometric values of a plurality of client fixed local transceivers, and determining a combined barometric correction value. The method further includes initiating a barometric correction value of the serving fixed local transceiver to the combined barometric correction value, and sending an indication of the barometric correction value to the plurality of client fixed local transceivers. The method further includes receiving a request for the serving fixed local transceiver barometric correction value from a target client fixed local transceiver, and sending the barometric correction value from the serving fixed local transceiver to the target client fixed local transceiver.

Abstract: A method and apparatus for using a predetermined portion of terrain elevation maps in a database for aiding in computing a three-dimensional position of a wireless station. Instead of using the entire terrain model of the earth or an entire country, the database consists of an incomplete model, which includes only the most populous areas or specific regions. This reduces the size of the information in the database, which in turn reduces the amount of time to compute the positions of the wireless device.

Abstract: The present invention discloses a radio beacon coupled to an altimeter, for GPS positioning in an elevator, configured to broadcast signals forcing a nearby GPS receiver to read constant latitude and constant longitude, associated with the position of the elevator shaft, and altitude associated with the altimeter reading. The acquired in-elevator position can serve as an initial fix for further navigation, particularly indoors.

Abstract: A method and device are provided for determining a target altitude for an emergency descent of an aircraft that is to be reached by the end of the emergency descent. The method includes determining an initial target altitude representative of the initial position of the aircraft and then repeatedly determining a current target altitude along a reference horizontal distance. The current target altitude is compared to the initial target altitude and is used to update the emergency descent if the current target altitude is lower than the initial target altitude. Each target altitude is selected as the larger of a predetermined threshold altitude and a security altitude that ensures any obstructions along a remaining horizontal distance are avoided.

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: Methods and systems for updating altitude information for a location by using terrain model information to prime altitude sensors are disclosed and may include determining an altitude of a wireless device including one or more altimeters. The determination of altitude may include determining a location of the wireless device, receiving an altitude value for the location from an altitude database, and measuring a change in the altitude using the altimeters. The database may include a worldwide terrain database that may be stored on a remote device, such as a server. Part of the database may be stored on the wireless device and may be updated as the wireless device moves. The location may be determined utilizing a global navigation satellite system, which may include GPS, GLONASS, and GALILLEO. The location may be measured utilizing cellular service triangulation or by utilizing one or more access points with known locations.

Abstract: The present invention is for a modular, extensible software system for use with multi-modal, autonomous, or semi-autonomous vehicles. The design of the present invention involves the coherent integration of modules with responsibilities for human-interaction, training, path planning, mission execution, navigation, and safety to develop and complete missions. The present invention provides a modular software system that expresses vehicle behaviors through numerous small-grain elements to complete a mission. The system can be easily adapted or modified by adding new software modules or modifying existing modules as missions change or expand, with the smaller-grain modules being easier to adapt and reuse.

Abstract: Method and device for monitoring a horizontal position of an aircraft rolling on the ground. The device (1) comprises an altimeter (3) and means (4, 6, 8, 10, 12) for detecting, with the aid of measurements carried out by the altimeter (3), an error of an indication of horizontal position emitted by a positioning device (2).

Abstract: The invention relates to an apparatus for finding a parked vehicle again. According to the invention, a portable unit is provided with a pressure sensor whose signals can be evaluated by an evaluation and control unit in order to determine the current air pressure, with the evaluation and control unit evaluating the determined air pressure in order to determine altitude, and storing a first air pressure value as a reference value at a predeterminable first time, which reference value represents an instantaneous altitude of a geographic position of the parked vehicle, with the evaluation and control unit estimating a height difference between a current geographic position of the portable unit and the geographic position of the parked vehicle at a second time, and/or continuously from a pressure difference between the determined current air pressure value and the reference value.

Abstract: The invention provides methods for validating a position of an airborne platform, by comparing rate of change of a measure of barometric altitude with rate of change of a measure of geometric altitude. When the difference in rates of change exceeds at least one predetermined threshold an indication is provided that a threshold has been exceeded. The methods may be employed onboard an aircraft and/or at an air traffic control site, provided the aircraft transmits the necessary parameters. The comparison not only provides validation of vertical positioning information (altitude) but also horizontal positioning information. Corresponding apparatus, systems, programs for computers, and communications signals are also provided.

Abstract: A ground-based CFIT warning system provides pilots with CFIT alerts. The system is based upon a ground-based tracking system, which provides surveillance of aircraft, such as the AirScene™ multilateration system manufactured by Rannoch Corporation of Alexandria, Va. The system monitors both horizontal and vertical positions of aircraft. When an aircraft has been determined to be operating below safe altitudes, or too close to obstructions, the pilot is provided with a warning. The warning may be delivered via the pilot's voice communications and/or a data link or the like.

Abstract: The altitude of a communications device, which communicates with a communications system via at least one antenna, is estimated. The altitude estimation is based at least on altitude information of said at least one antenna. The altitude estimate of the communications device may be based on a two-dimensional location estimate for the communications device and on information representing three-dimensional location of said at least one antenna of said communication system. The two-dimensional location estimate and the altitude estimate may be sent to the communications device as location assistance information.

Abstract: Apparatus and process for determining the position and heading or attitude of an antenna array are described based on radiating sources, preferably GNSS or other such satellite positioning systems. An optimum satellite is selected and the antenna array is “null steered” by combining the phase of the received signals to calculate a null or null angle that points toward the optimum satellite. The null will determine angle for elevation toward the optimum satellite and azimuth or heading. The heading is the azimuth of the (which may be actual or calculated) projection of the null vector to the satellite onto the Earth's surface. The actual location on Earth of the antenna array can be found and the antenna array azimuth with respect to the satellite can be determined. The null angle may be measured more precisely by dithering on either side to average out noise and then averaging the angle deviations to calculate the null angle.

Abstract: A wireless system and method for locating the position of a movable signal emitter located inside or adjacent to a structure includes establishing at least three base station sites at known locations around the structure. The signal emitter then transmits an omni-directional, low frequency, RF signal that is received at the base station sites. Phase information is measured at each base station site and communicated to a central processing site. At the central processing site, relative phase delays are used to geometrically calculate the position of the signal emitter.

Abstract: A method for calculating a center frequency and a bandwidth for a radar doppler filter is herein described. The center frequency and bandwidth are calculated to provide radar performance over varying terrain and aircraft altitude, pitch, and roll. The method includes receiving an antenna mounting angle, a slant range, and velocity vectors in body coordinates, calculating a range swath doppler velocity, a track and phase swath bandwidth, and a phase swath doppler velocity. The method continues by calculating a range swath center frequency based on the range swath doppler velocity, calculating a phase swath center frequency based on the phase swath doppler velocity, and calculating a level and verify swath bandwidth based upon the track and phase swath bandwidth.

Abstract: A wireless telecommunications network uses a wireless location technology to determine the locations of mobile stations. As part of a location accuracy analysis process, the wireless location technology is used to obtain a measured latitude and longitude for a mobile station located at a test site having a known latitude and longitude. A data analysis system calculates the radial location error, expressed as a distance, between the measured and known latitude and longitude values. The process is repeated a number of times sufficient to calculate the mean radial location error to within a predetermined uncertainty at a predetermined confidence level.

Abstract: A method is disclosed for obtaining altitude-related data along roads. A vehicle includes equipment capable of determining the current absolute positions of the vehicle as it is being driven. The vehicle also includes equipment capable of determining a distance traveled by the vehicle. Two points along a road are selected. Altitude-related data are determined as a function of the horizontal difference between the absolute positions of the two points and the distance traveled by the vehicle between the two points.

Abstract: A vehicle data bus system includes locating means which comprise a locating computing unit and a locating sensor system which contains at least one GPS receiver with associated GPS antenna and gyro data acquisition means, and a data bus via which connects a plurality of bus users in data communication with one another. The locating means contain a locating module which is embodied as one of the bus users and is configured to receive at least wheel speed data and forward/backward direction of travel data via the data bus, to acquire at least vehicle position data, direction of travel angle data, travel speed data and altitude position data as well as to output this acquired data onto the data bus. For this purpose, the locating module contains the location computing unit, the GPS receiver and a gyroscope or means for the bus-end reception and evaluation of gyro data of a travel dynamics/traction control system.

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: The invention relates to a method and arrangement for positioning one or more mobile stations, in which the location of the mobile stations is determined in the horizontal direction using at least two radio direction finding stations. Information on the location of each mobile station is maintained on a server. The mobile station measures at least one variable proportional to the location of the mobile station in the vertical direction and signals information on the measurement results to a control unit time-divisionally at the same frequency controlled by the control unit. In the control unit the location of each mobile station is determined in the vertical direction on the basis of the signalled data and the data on the location is conveyed to the server, where the three-dimensional location of the mobile stations is determined. The locations of at least some of the mobile stations are displayed graphically.

Abstract: A method and system for tracking an object by generating GPS coordinates for the object and a bearing associated with a movement of the object. The GPS coordinates include a latitude, a longitude, and an altitude, which are processed. The GPS coordinates can be processed to correlate the altitude of the object with an identifier that identifies a level within a structure. An icon representing the object then can be accurately located in a first view of a three dimensional model. An indicator can be associated with the icon to indicate the object's level, a bearing of the object, and/or the object's GPS coordinates. The object's GPS coordinates can be compared with a second object location to determine dispatch instructions. The object can be a person, a vehicle, watercraft or an aircraft.

Abstract: A communication method and system for transmitting a real data signals is provided. In one aspect, the location of a communications device is determined. At least two transmitter/receiver devices are provided. A first data signal is transmitted from the communications device to the at least two transmitter/receiver devices. The data signal is received only by both receivers in combination, and with the knowledge of the location of the communication device, time delays associated with the position of the communications device are accounted for. Alternatively, a portion of a signal is sent from each of the at least two transmitter/receiver devices to the communications device, and are combined at the communications device, whereby knowledge of the location of the communication device allows time delays associated with the position of the communications device to be accounted for.

Abstract: An apparatus, system, method and computer program product to verify proper operation of an aircraft altimetry system. Aural and visual alerts may optionally be provided when a fault in the altimetry is detected.

Abstract: A method for performing Earth altimetry comprising the steps of: receiving by an upward-looking antenna onboard a platform above the Earth surface, direct signals having at least two different carrier frequencies transmitted by GNSS satellites in view of the upward-looking antenna, receiving by a downward-looking antenna onboard the platform signals reflected by the Earth surface and having the at least two different carrier frequencies, comparing carrier phases of the direct signals and received reflected signals, at the carrier frequencies, and determining from the phase comparisons a surface height.

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: Disclosed is a communication device and method for estimating a more accurate vertical position or altitude of a communication device using atmospheric pressure measurements. In one embodiment, a first communication device comprises a pressure sensor for measuring local atmospheric pressure at the first communication device and a transceiver for communicating with a second communication device, wherein the transceiver may be operable to receive barometric calibration information for calibrating a local atmospheric pressure measured at the first communication device and/or to transmit the measured local atmospheric pressure to the second communication device. The first communication device may further comprise a processor for estimating an altitude using the measured local atmospheric pressure and received barometric calibration information.

Abstract: A method for performing Earth alimetry comprising the steps of: receiving by an upward-looking antenna onboard a platform above the Earth surface, direct signals having at least two different carrier frequencies transmitted by GNSS satellites in view of said upward-looking antenna, receiving by a downward-looking antenna onboard said platform signals reflected by the Earth surface and having said at least two different carrier frequencies, comparing carrier phases of said direct signals and received reflected signals, at said carrier frequencies, and determining from said phase comparisons a surface height.

Abstract: A system for wind profiling comprises sondes for being borne through the atmosphere by balloons and transmitting signals enabling identifying the sondes, and received by receivers capable of determining the angle of arrival (AOA) of the signals from the sondes, so that they can be tracked. In the preferred embodiment, the signal transmitted by each sonde is a phase-shift-keyed (PSK) signal. The carrier phase difference as measured at two spaced antennas is measured to provide an accurate but ambiguous measure of the difference in distance of the path length between the sonde and receivers, and the symbol phase difference is employed to remove the ambiguity. The difference in path length is then used to determine AOA. Atmospheric data and the sonde identification are encoded using a psuedo-random sequence (PRS) of the PSK symbols.

Abstract: A method and apparatus for determining a position of a mobile satellite positioning system (SPS) receiver. In one example of a method, a cell object information is determined; this cell object information comprises at least one of a cell object location or a cell object identification. An altitude is determined from the cell object information which is selected based upon a cell site transmitter which is in wireless communication with a cell based communication system which is coupled to (and typically integrated with) the mobile SPS receiver. The position of the mobile SPS receiver is calculated using the altitude which is determined from the cell object information. In another example of a method, an altitude pseudomeasurement is determined from an estimate of an altitude of the mobile SPS receiver.

Abstract: A system and method for improving the accuracy of altitude determinations in an inertial navigation system. The system utilizes pressure measurements which are taken by a barometric altimeter and converted into an estimated pressure altitude using any known pressure-to-altitude conversion. A pressure correction value is then generated using a correction value generating formula that is a function of altitude. The pressure correction value is then multiplied by a pressure offset value for the barometric altimeter to generate a pressure offset error for the barometric altimeter. This pressure offset error is used in the present invention to modify the pressure altitude estimation in order to generate an altitude determination having an improved accuracy. The present invention further determines an amount of observation noise in the barometric altimeter that is a function of pressure noise and altitude, where the altitude estimation is further modified to account for the observation noise.

Abstract: An anti-collision system is provided to enhance the conspicuousness of an aircraft to a second aircraft presenting a collision threat. When the computer of an airborne Traffic Collision Avoidance System (TCAS) designates a second proximately located aircraft as a collision threat a traffic advisory is issued. A light controller responds to a traffic advisory signal from the TCAS computer by illuminating one or more of the aircraft's external lighting systems. TCAS II systems can also issue resolution advisory when the intruder poses a more immediate threat. A resolution advisory signal from the TCAS computer can be used to alter the lighting systems being activated or the rate of flashing to make the aircraft more noticeable. Alternating illuminating and obscuring of landing lights, taxi lights, deicing lights, strobe lights or rudder illumination lights enhances the conspicuousness of the aircraft to the crew of a second aircraft seeking to avoid a collision.

Abstract: A method and apparatus for determining the orientation of an object relative to a reference magnetic field includes establishing generally adjacent to the object a modifiable magnetic field. The direction of the modifiable magnetic field is changed among a plurality of predetermined, known orientations relative to the object. A resultant magnetic field, including the reference magnetic field and the modifiable magnetic field, is repeatedly measured adjacent to the object. The step of measuring is directed outwardly from adjacent to the object in predetermined directions that are fixed relative to the object to determine when the magnitude of the resultant magnetic field is minimized or maximized indicating that the direction of the modifiable magnetic field is parallel with that of the reference magnetic field. Thereupon, the orientation of the object is correlated to the known orientation of the modifiable magnetic field.

Abstract: A method and a system for determining an altitude of an object of interest, for example, an airplane that transmits electromagnetic radiation in the form of radar signals. A number of sub-units that can detect the radar signals are spread out in an area, preferably in a large geographical area, where the radar signals of the airplane/object it is possible to detect. The sub-units communicate to the information center when they are able to detect the radar signals. The information center determines the altitude of the airplane based on the airplanes line of sight, i.e., its radar horizon, and thus which sub-units can detect the radar signals.

Abstract: Methods and apparatus for determining altitude, specifically altitude in an aircraft, and an estimated error of the altitude. The altitude determination preferably uses a first altitude based on hydrostatic calculations, including local pressure and temperature, as well as a second altitude which is preferably a GPS altitude. A radio altimetry can also be used instead of or to complement the GPS altitude. Other sources of altitude determination can be used in the equation for the calculation of the final altitude. Each of the sources of altitude determination is provided with a complementary estimated error. In the final determination of the probable altitude, each source of altitude information is preferably accorded a weighting according to the estimated error of the altitude source. For global positioning altitude, the final combination of the altitude sources uses a complementary filter which takes into account the selective availability of the GPS altitude.

Abstract: The invention is a method for determining gravity in an inertial navigation system which periodically produces and stores in memory position coordinates. The method comprises the steps of (a) retrieving the most recently determined position coordinates, (b) determining coordinates L.sub.u, L.sub.n, H.sub.u, and H.sub.n from the position coordinates, L.sub.u and L.sub.n being predetermined functions of geodetic latitude and H.sub.u and H.sub.n being predetermined functions of geodetic altitude, (c) determining the vertical component of gravity by substituting either or both L.sub.u and H.sub.u in a first polynomial expression, (d) determining the north-south component of gravity by substituting either or both L.sub.n and H.sub.n in a second polynomial expression, and (e) utilizing the components of gravity determined in steps (c) and (d) in the next determination of the position coordinates.

Abstract: A method and apparatus for determining a position of a mobile satellite positioning system (SPS) receiver. In one example of a method, a cell object information is determined; this cell object information comprises at least one of a cell object location or a cell object identification. An altitude is determined from the cell object information which is selected based upon a cell site transmitter which is in wireless communication with a cell based communication system which is coupled to (and typically integrated with) the mobile SPS receiver. The position of the mobile SPS receiver is calculated using the altitude which is determined from the cell object information. In another example of a method, an altitude pseudomeasurement is determined from an estimate of an altitude of the mobile SPS receiver.

Abstract: A method for calibrating a pressure-sensing altitude sensor of an aircraft while the aircraft is in flight. The method includes the steps of obtaining a set of reference atmospheric pressures as a function of height above a base station by affixing a reference pressure sensor to a balloon. As the balloon is released into the atmosphere, the reference sensor continuously measures the atmospheric pressures and transmits the data back to the base station while a ground-based radar disposed adjacent the base station measures the height of the balloon. An aircraft flying in a vicinity of the base station can calibrate its pressure-sensing altitude sensors by measuring the atmospheric pressure outside the aircraft and its geometric height relative to the base station and then comparing the pressure measurements with corresponding reference pressure values at a geometric height that is substantially that same as the geometric height of the aircraft.

Abstract: A calibration system for a pilot warning system includes first and second calibration antennas spaced apart on an aircraft. The first and second calibration antennas receive the same pulsed RF signal, suitable delayed so that, after emission from the calibration antennas, the pulsed signal is received at times at antennas of the pilot warning system appropriate to indicate that a simulated target is within or outside (up or down) an elevation angular band of interest. Adjustment of relative timing is made by inducing relative transmission delays of the pulsed signal on its way to the two antennas. In one embodiment, different cable lengths produce the desired delays.

Abstract: Method and apparatus for determining the attitude or angular orientation of a moving vehicle or other moving body, using either two spaced apart antennas or a single antenna attached to or connected with the vehicle. Where two antennas are used, the spatial locations of each antenna are determined at a first selected time, and the spatial location of one antenna is determined at a second selected time. These three spatial locations determine a plane whose normal vector allows determination of the vehicle attitude at a time determined by the first and/or second selected times. Four or more spatial locations can also be used to determine a plane that indicates vehicle attitude. Where one antenna is used, for example, in a vehicle turn, the antenna spatial locations at three distinct selected times determine a plane that allows determination of the vehicle attitude at a time determined to the first, second and/or third selected times.

Abstract: An enhanced system for calculating the Z-Axis, or relative height or altitude, of a radio beacon. The present invention uses a barometric pressure sensing device co-located with the radio emitter to transmit data representing relative altitude. To further enhance the Z-Axis determination, one or several barometric sensors, located at known heights, are positioned around the city to provide real time barometric data. This real time data is used to form a differential correction factor which is compared to the to the time varying barometric sensor co-located with the radio emitter, thereby yielding Z-Axis accuracies of up to one (1) foot. Since the altitude essentially becomes a "known", this information can also be used in the least squares fit algorithm to enhance the X and Y determination as well.

Abstract: This invention relates to a system to alert an aircraft pilot of the presence and general location of other aircraft that might constitute a collision threat to the pilot's aircraft. A first and second antenna on the upper paid lower surfaces of the aircraft each operate in first and second modes characterized by respective first and second directivity conditions. The first and second antennas directly receive pulse signals from a source in order to determine the relative time of arrivals and thus the relative altitude of the source to the aircraft. Analysis means compares amplitudes of responses in the first and second modes to provide an angle indicating signal without having to generate radio signals other than those already being generated by equipment in the other aircraft in response to ground ATC interrogation.

Abstract: It is determined that an altitude of a vehicle can not be calculated from data applied from satellites. When the calculation can not be performed, a provisional altitude is obtained with a following equation:H=(1-.alpha.)H.sub.G +.alpha.H.sub.Owhere H.sub.G is an altitude obtained by the GPS, H.sub.O is a reference altitude obtained by the outside means, .alpha. (O<.alpha.<1) is a predetermined smoothing coefficient.

Abstract: A system and method for determining the position of an airborne object, using a fixed station and a pair of earth orbit satellites whose positions are known. Separate periodic signals are transmitted from the fixed station via the first and second satellites to the object whose position is to be determined. The phase offset in periodic characteristics of the periodic signals as received from the first and second satellites is measured at the object. The phase offset corresponds to a realtive time difference in propagation of the signals traveling two different paths to the object. The object transmits via the first satellite a return signal indicative of the measured relative time difference. This return signal is activated some time in the future according to the object local time, which is slaved to receipt of the periodic signal sent through the first satellite. This future time is the start of the particular time period as decided by the fixed station's schedule.

Abstract: A radio position determation and message transfer system is implemented using a pair of satellites in geostationary orbit for replaying interrogation and replay signals between a ground station and a user-carried transceiver. The user portion is calculated based on the arrival times of replay signals received at the ground station via the two satellites, the known transmission time of the interrogation signal from the ground station, and the user's elevation on the surface of the earth. The elevation is derived from a stored terrain map providing local terrain elevations at a plurality of points of the earth's surface. The stored terrain map allows accurate position fixed to be obtained for surface users regardless of the deviation of the local terrain from the spherical or ellipsoidal model of the earth's surface.

Abstract: A method for determining the flight altitude h above ground of an aircraft equipped with a radar altimeter and an additional (baro-inertial) altitude measuring device or a course and position reference system capable of determining altitude. The method relies upon restriction of high-frequency emissions from the radar altimeter to very short periods of time. The radar altimeter measures h.sub.RO within the high-frequency intermission intervals to calibrate the altitude value supplied by the other altitude-measuring device. The method permits the omission of any radar altimeter from aircraft-launched missiles without degrading system performance.

Abstract: The moving map display screen makes it possible to display the relief of the area overflown by an aircraft as a function of the altitude of the latter.A moving-spot video reader analyses by radial scanning the relief of the area to be overflown and recorded on a film. In a processing circuit, the instantaneous altitude of the analyzed point is supplied in digital form to three comparators, where it is compared to three different values as a function of the aircraft altimeter. The result of this comparison makes it possible to classify this altitude in a range relative to the instantaneous altitude of the aircraft. A transcoder allocates to each range a particular digital value corresponding to a given shade. A display means reproduces the relief of the analyzed area with the aid of several conventional shades.

Abstract: An aircraft position determining system including an on-board radio altimeter which cooperates with a ground based transponder/beacon located at a position A. The radio altimeter is adapted as a distance meter and comprises means (9, 14, 15, 16) for shifting the frequency of the local oscillation signal. The system has a range sufficient to enable it to operate in a second predetermined volume defined with respect to the position A which includes a first volume defined by the lateral distance accuracy (d) and vertical distance accuracy (h) of the position determined by an independent on-board guidance device. The exact position of the aircraft when close to A is determined by at least two successive measurements of distance from to the position A.