Abstract: A process for measuring the relative distance and speed of an object in relation to a periodically frequency-modulated continuous wave radar includes extracting the distance and the speed by combining beat frequencies derived from a mixture of emitted and reflected signals being respectively obtained during ascending and descending alternations of a modulation. The distance and the speed of an object at each half-period are calculated from beat frequencies of two immediately preceding alternations.

Abstract: When measuring speed over ground by means of microwave Doppler radar, signal noise, switching spikes and nearby reflectors reduce the measurement accuracy. In order to avoid these disadvantages, a reference signal which recurs with the period T.sub.0 and a target signal which follows the reference signal after a time interval T.sub.s are emitted via an antenna. That part of the reference signal which has already been received again during transmission of the target signal is subtracted from the target signal which is received later. The difference signal obtained in this way is a measurement signal from which interference spikes, signal noise and nearby reflectors have been largely removed.

Abstract: A vehicle radar emits four groups of single-frequency stepped radar pulses. In group A, the frequency of each pulse is a fixed amount higher than that of the preceding pulse. In group B, the frequency of each pulse is a fixed amount lower than that of the preceding pulse. In group C, the frequency of each pulse is the same as that of the preceding pulse. In group D, the frequency of each pulse depends on a modulo algorithm. The signals reflected from other vehicles may readily be processed with inexpensive equipment to discriminate among such other vehicles, and to determine the distance to, and relative speed of, each such vehicle.

Abstract: A radar device secured to a vehicle includes a transmitter for broadcasting continuously frequency-modulated radar signals over a time range. The time range is fixed as a function of a speed of the vehicle and is longer at a higher speed and shorter at a lower speed. A receiver receives the radar signals. An evaluation circuit compares the transmitted and received radar signals to ascertain information about the surroundings and in particular a distance from and a relative speed with respect to an object.

Abstract: An FM-CW radar which is suitable for automotive anti-collision systems, for example, is provided. This radar outputs a radar signal in the form of a triangular wave whose frequency is increased at a given rate and decreased at a given rate. A receiver receives a wave reflected from a target to produce a beat signal and takes the Fourier transform of the beat signal to determine peak frequency components thereof showing peaks in a frequency spectrum. The receiver also determines phases of the peak frequency components and selects at least one from the peak frequency components in a frequency-rising range wherein the frequency of the radar signal is increased and at least one from the peak frequency components in a frequency-falling range wherein the frequency of the radar signal is decreased which show substantially the same phase to pair them for determining the distance to and relative speed of the target based on the frequency of the paired peak frequency components.

Abstract: A system and method for determining wind velocity. The LIDAR 104 transmits a plurality of laser pulses. The paths of the laser pulses surround a center line (206) that does not coincide with a vertical axis (706) intersecting the LIDAR (104), i.e., an off-vertical scan. Each laser pulse reflects off particles in the air at a given location. This location is the intersection of the path of each LIDAR pulse and the target altitude. The target altitude is the altitude at which the wind velocity is to be determined. The reflected pulses are received by the LIDAR (104). The invention groups the received LIDAR pulses according to the altitude at which they were reflected, as opposed to the distance each pulse travels. Grouping the received pulses in this manner enables the invention to perform an off-vertical scan that accurately determines the wind velocity at a target altitude. The received laser pulses have an associated Doppler shift.

Abstract: A system and method for determining absolute vehicle height and ground speed. As disclosed, a millimeter wave radar system for determining selected boundary distances is implemented based upon a generation of a modulated millimeter wave signal which is envelope detected and thereafter phase detected to determine the selected boundary distance on a continuous real-time basis. To similarly determine absolute vehicle speed on a continuous real-time basis, a method is disclosed for use in cooperation with an on-board microcomputer, the height sensing system described above, and a passive speed sensor aperture which is affixed to the chassis and directed toward the ground at some angle theta. In operation, a portion of the RF signal radiated by the height sensor is backscattered toward the passive speed sensor aperture. The Doppler Shift of this signal caused by vehicle motion is determined.

Abstract: A radar apparatus for detecting a distance/velocity has a transmitting system for transmitting a signal which is frequency-modulated with a modulating signal having a predetermined recurrence frequency, a receiving system for receiving a reflected wave signal, which is the modulated transmission signal transmitted from the transmitting system and reflected by an object, and which mixes the reflected wave signal and the modulated transmission signal from the transmitting system so as to detect a beat wave signal of the reflected wave signal and the modulated transmission signal.

Abstract: A method and device of the pulse-compression radar or sonar type which makes it possible to determine the speed of a moving object is provided with a transmitter system, a receiver system, and a signal processing system. The transmitter system is capable of transmitting two associated pulses, one of which is modulated with an increasing variation law and the other of which is modulated with a decreasing variation law. The signal processing system includes two correlators, an adder, a subtractor, and a computer.

Abstract: A control system for use with an electronically-controlled automatic transmission provides for accurate determination of a full stop of a vehicle. The control system includes a device for computing the vehicle speed on the basis of a signal from a vehicle speed sensor, a device for determining whether or not the brake pedal is depressed, a device for computing deceleration from a first predetermined vehicle speed to a second predetermined, extremely low vehicle speed when the brake has been determined to be depressed, and a device for determining an estimated vehicle stop time starting with detection of the extremely low vehicle speed and ending with full stop of the vehicle, the estimated vehicle stop time corresponding to the above-computed deceleration.

Abstract: A cost-effective FMCW radar equipment has a digital signal processor which controls at least one antenna through an oscillator and produces a mixed signal from transmitted and received signals modulated with a triangular waveform. The mixed signal is subjected to Fast Fourier transformation for each modulation phase (up and down) of each measurement cycle in order to obtain object frequencies, which are assigned to each target object, from the determined maxima. Object tracks which are formed from the object frequencies extend back over a plurality of measurement cycles and are used to form estimated values for those measured values of the object frequencies which are to be expected in the next measurement cycle. The mutually associated object frequencies of both modulation phases of a measurement cycle are determined and the distance and relative speed of each target object are determined from them.

Abstract: An automobile collision avoidance system based on laser radars is disclosed for aiding in avoidance of automobile collisions. The very small beam width, very small angular resolution and the highly directional character of laser radars provide a plurality of advantages as compared with microwave radars. With two sets of laser radars this system can detect the location, the direction of movement, the speed and the size of all obstacles specifically and precisely. This system includes laser radars with transmitters and receivers, a computer, a warning device and an optional automatic braking device. A steering wheel rotation sensor or a laser gyroscope is utilized to give information of system-equipped vehicle's directional change. The system will compare the predicted collision time with the minimal allowable time to determine the imminency of a collision, and when determined, provides a warning. An optional automatic braking device is disclosed to be used when the vehicle user fails to respond to a warning.

Abstract: A laser speed detector is described which includes a laser rangefinder which determines the time-of-flight of an infrared laser pulse to a target and a microprocessor-based microcontroller. The device is small enough to be easily hand-held, and includes a trigger and a sighting scope for a user to visually select a target and to trigger operation of the device upon the selected target. The laser rangefinder includes self-calibrating interpolation circuitry, a digital logic-operated gate for reflected laser pulses in which both the "opening" and the "closing" of the gate can be selectably set by the microcontroller, and dual collimation of the outgoing laser pulse such that a minor portion of the outgoing laser pulse is sent to means for producing a timing reference signal.

Abstract: A cruise control system for a vehicle includes a vehicle borne radar for determining range and closing rate of the vehicle relative to a target, such as another moving vehicle, ahead of the vehicle. The range and closing rate are used to determine a new set speed for the cruise control system which may be less than but is not greater than the speed entered in the cruise control by the driver of the vehicle. The new set speed is selected to prevent the vehicle from overtaking the target, and ideally reduces the closing rate to zero at a predetermined minimum distance from the target. In determining the new set speed, the system also determines incremental movements for the vehicle throttle using a selected gain boost and designed to minimize throttle jerk. If the target moves out of the path of the vehicle or speeds up, the system adjusts accordingly and eventually allows the vehicle to resume the originally entered speed when possible.

Abstract: Frequency-modulated wave trains are used in target locating by means of transmitted pulses and evaluation of portions reflected by the target in relation to bearing, distance and speed, wherein the pulse length and bandwidth of the transmitted pulse are pre-selected. The received signals are evaluated in Doppler channels by calculation of the ambiguity function. To make possible an increase in accuracy of the speed determination with the same number of Doppler channels, the frequency of the wave train within the bandwidth is calculated in accordance with an irrational function, the exponent of which has a value between 0 and 1. The smaller the value, while keeping the same pulse length, the greater the Doppler sensitivity. This method for modulating the wave train in the transmitted pulse can be advantageously employed for target identification by means of sound waves and electromagnetic waves.

Abstract: A method and apparatus for identifying a remote target includes a transmitter for transmitting pulses of energy toward the target for generating echo signals, and a receiver for receiving the echo signals, and for generating received signals representing the target, noise and clutter. The received signals are applied through a plurality of cascaded channels, each including a Doppler filter cascaded with a multiplier, each also including range sidelobe suppression, for, in each of the cascaded channels, narrowband filtering the signals passing therethrough about a controllable center frequency, and for, if necessary, converting the signals passing therethrough to baseband, for thereby applying one of a plurality of Doppler filtered baseband signals to the input of each of the range sidelobe suppressors of each of the cascaded channels. The power of the Doppler filtered baseband signals in each range bin is evaluated for determining the frequency at which the spectral density is greatest.

Abstract: A method for determining velocity of a target object comprises transmitting a propagating wave emitted from a wave transmitter and detecting a reflected wave reflected back by the target object by using a wave receiver, and determining of a phase angle difference between two alternating electrical signals respectively representing the transmitted wave departing the wave transmitter and the reflected wave arriving at the wave receiver, wherein the velocity of the target object is determined as a function of the time rate of change of the phase angle difference between the two alternating electrical signals.

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 radar system (10) forms a range-Doppler map (28). A CFAR processor (57) determines a threshold (60) and evaluates the map (28) to identify potential targets whose amplitudes are greater than the threshold. The potential targets are evaluated to determine (88) whether they form substantial peaks for the Doppler bins (32) where they are located, and to determine (98) whether they resemble noise more than targets. In addition, the potential targets are evaluated to determine (114) whether they are most likely the result of range sidelobes and to determine (118) whether they are most likely images of targets rather than targets. When any of these situations are detected, the potential targets are removed from a potential target list (50).

Abstract: The present invention provides a method and apparatus for determining a desired parameter of the motion of an object. In one embodiment, the device can be used to calculate the estimated carry distance of a golf shot. The golfer uses a keypad to enter the golf club and the units of measure for the output display. A Doppler radar system is employed to illuminate the golf ball. A reflected return signal is detected and difference pulses are generated, having a frequency which is proportional to the velocity of the ball. The difference pulses are processed by a microprocessor to determine if the radar beam has "locked" onto the ball. If so, the microprocessor calculates the carry distance by relating the average period of the difference pulses to a projected carry distance through empirically determined data. The carry distance can be displayed on the device, on a remote display, and/or can be stored in memory for later recall or transmission to an external computer.

Abstract: A FM-CW radar device is provided for frequency-modulating a high frequency signal with a modulation signal, transmitting the modulated high frequency signal, receiving a signal reflected by a target object and frequency-modulating the reflection signal with a signal generated by a local oscillator signal source provided by branching a portion of the transmitting signal. A modulator is disposed between a radar transmitting section and a transmitting antenna. The modulator modulates the transmitting signal with a second frequency which is far lower than the radar transmitting frequency and twice as much as the sum or the difference of a Doppler frequency generated by a relative propagation velocity and a beat frequency generated by a propagation delay time. A first frequency converter frequency modulates the received signal reflected by the target object with the local oscillator.

Abstract: A method of displaying and determining the velocity of radar returns of frequency modulated continuous wave radars including the steps of determining a velocity for each radar return from a detected beat frequency associated with received radar returns, and displaying (for successive radar dwells) one or more major plots indicating range, azimuth and velocity of any radar returns. Each major plot is characterized by a velocity axis with a maximum and a minimum display velocity. The major plots are composed of minor plots indicating range, azimuth and velocity of any radar return and are characterized by a velocity axis that extends between zero velocity and the magnitude of greatest possible velocity corresponding to the range of the detected beat frequencies.

Abstract: An automobile collision avoidance system based on laser radars for aiding in avoidance of automobile collisions. The very small beam width, very small angular resolution and the highly directional character of laser radars provide a plurality of advantages as compared with microwave radars. With two sets of laser radars this system can detect the location, the direction of movement, the speed and the size of all obstacles specifically and precisely. This system includes laser radars with transmitters and receivers, a computer, a warning device and an optional automatic braking device. A steering wheel rotation sensor or a laser gyroscope is utilized to give information of system-equipped vehicle's directional change. The system will compare the predicted collision time with the minimal allowable time to determine the imminency of a collision. When the system determines that a situation likely to result in an accident exists, it provides a warning.

Abstract: The invention relates to the simultaneous determination of the distance and the speed of a target in a radar system that operates according to the HPRF (High Pulse Repetition Frequency) method. A target spectrum group is determined in the Doppler domain and the distance of the target is then determined from the group delay.

Abstract: The present invention relates to a signal processing method for a radar system. The transmitted signal here includes a polyphase code that is optimized to the desired range/Doppler range and that is repeated periodically over time.

Abstract: The present invention provides a method and apparatus for determining a desired parameter of the motion of an object. In one embodiment, the device can be used to calculate the estimated carry distance of a golf shot. The golfer uses a keypad to enter the golf club being used and the units of measure desired for the output display. A Doppler radar system is employed to illuminate the golf ball immediately after it has been hit. A reflected return signal is detected and difference pulses are generated, having a frequency which is proportional to the velocity of the ball. The difference pulses are processed by a microprocessor to determine if the radar beam has "locked" onto the ball. If so, the microprocessor is used to calculate the carry distance by dividing a predetermined constant by the average period of the difference pulses. The carry distance can be displayed on the device itself or on a remote display, and/or can be stored in memory for later recall or transmission to an external computer.

Abstract: Radar signal processor for the detection of fast moving targets having small radar cross-sections. A method and apparatus is used to analyze a target that may travel through many range cells during coherent integration time. By transforming the pulse return data into the spatial frequency domain, range bin migration problems have been solved. The signal to noise ratio is also improved thereby permitting the detection of small targets. The processing consists of three major steps: performing an FFT for each pulse to yield spatial frequency components for each return; performing a special DFT for each spatial frequency yielding constant velocity output for each spatial frequency; and finally performing an inverse FFT to obtain target velocity and position.

Abstract: A continuous-wave radar set is additionally usable as a transmitter for transmitting messages, e.g., voice, data, or control information. Besides a first modulator (SM) which produces a sawtooth or triangular frequency modulation of the radar RF signal, there is an additional modulator (ZM) which modulates the radar RF signal with a useful signal during the flyback, i.e., in a phase in which the signal is not used for radar purposes. To achieve exact synchronization between the two modulators, both modulators are controlled by the same clock generator (T).

Abstract: False target (reverberation, clutter, etc.) detection is suppressed in an echo ranging system (sonar or radar) in which target velocity and range are measured using a composite Doppler invariant-like signal having at least two segments, such as are present in a "rooftop" or "vee" HFM signal, such composite signal having an ambiguity function with two or more ridge lines of different slopes that intersect along the zero-velocity time axis. A bank of matched filters provides a distribution of outputs which has an ambiguity function-like character with intersecting pairs of ridge lines, the intersecting points of said pairs characterizing the range and velocity of the echo returns. This distribution is adjusted so that the intersecting ridge lines of each pair have equal and opposite slopes with respect to the time axis. In particular, fixed reverberators, which would have ridge lines intersecting on the zero-velocity time axis, would be symmetrical about this axis.

Abstract: Target velocity and range are measured with high resolution in an echo ranging system (sonar or radar) using composite Doppler invariant signals consisting of at least two segments, such as "rooftop" or "vee" HFM signals, such composite signals having ambiguity functions that intersect along the zero-velocity time axis with ridge lines slanted in different directions. A single correlator is used for each segment wherein returns from the target are correlated with replicas of each segment of the composite signal to separately transform the Doppler frequency shifts of the target return into outputs whose time relationship provides a frame of reference for high resolution measurement of the velocity of the target. The time relationship measurement is implemented by a set of tapped delay lines and coherent summers which output a coherent correlation-like detection peak in a bin which corresponds to the target's velocity.

Abstract: An airborne bistatic radar synchronization apparatus and process is presented which receives clutter point echo returns from the bistatic radar receiver on a penetrator aircraft, and determines therefrom the location of the illuminator aircraft without the need of receiving direct path signals from the radar transmitter on board the illuminator aircraft. Once the state of the illuminator aircraft (position and velocity) has been determined, the estimate of the illuminator state may be refined using direct path data. Finally, a target location algorithm is applied to bistatic target echo returns to calculate an equivalent monostatic range for a desired target, and provide an estimate of the location of the target.

Abstract: A coherent pulse radar system capable of eliminating a signal associated with a multiple time around path or capable of removing range ambiguity of this multiple time around signal. The radar system includes a device for changing phases of transmitted pulses, for phase detecting received radar pulses with respect to transmitted pulses associated with the present and preceding reception period, and for integrating phase detected signals in a coherent manner.

Abstract: A transmitter section of the arrangement includes an altimeter transmitter and a Doppler transmitter. The transmitters both provide frequency-modulated outputs. The altimeter transmitter is linear-FM while the Doppler transmitter is sine-FM.

Abstract: An electronic proximity fuse of the FM radar type having a detonating circuit with two inputs. One input is derived from a signal representing the amount by which the frequency of the received signal differs from the frequency of the transmitted signal at the instant of reception averaged over the frequency-modulation period. The second input is derived from a signal proportional to the amount of the frequency fluctuations of the frequency deviation about the averaged amount.

Abstract: A passive doppler differential ranging method for use with respect to an aircraft radar for determining the range, R, of a threat passively, includes the steps of mounting a first receiving antenna and a second receiving antenna on an aircraft and positioning the first and second antennas a known distance, d, apart from each other, and determining the azimuth angle .alpha. of the threat with respect to the aircraft at a first time t.sub.o. A first differential doppler phase shift, .DELTA..phi., between the first and second antennas of a received signal transmitted by the threat at time t.sub.o is then determined. The velocity of the aircraft is measured, and a second differential phase shift, .DELTA..phi..sub.1, between the first and second antennas of a received signal transmitted by the threat at time t.sub.1 is then determined. The differential differential doppler phase shift, .DELTA..DELTA..phi.

Abstract: With a frequency-agile pulsed doppler radar with high pulse repetition frequency (HPRF) in the unambiguous velocity region, in order to measure the range of a target the complex time signal derived from the echo signals of a coherent processing interval (CPI) is transformed into the frequency domain, the transformed spectrum is multiplied by a bandpass function with a mean frequency coinciding with the doppler frequency of the target, and the product is transformed back into a time signal. The real envelope of this re-transformed time signal displays a definite leading edge and a steady state region, from which the echo travel time can be estimated. Particular advantages may be derived for the pulsed doppler radar set from a plurality of frequency agile transmitter/receivers operated at the same time at different frequencies, and whose frequency switching times are time-staggered.

Abstract: A radar system for monitoring the headway control distance between a vehicle equipped with a radar system of the present invention and a fixed or moving object of immediate concern in front thereof. The system employs an antenna positioned in front of the vehicle, transmitter and receiver circuits and signal processing circuits. A transmitted signal from the transmitter circuit when reflected back from an object of immediate concern is received by the receiver circuit and fed into conditioning circuits which separate the received signal into controlling signals that include the range or distance (R) to a detected object of concern, the closing rate (CR) to that object and the vehicle speed of movement (VS). Driving condition modifiers (.+-.

Abstract: A coherent laser radar system in which a number of individual receiver modules are deployed in an area relatively near the targets to receive signals originating at a transmitter located at a much greater distance from the target area. The radar is particularly adapted for the midcource detection and tracking of missiles in space and differentiating between reentry vehicles and decoys. This permits a number of receivers to be positioned at separate points, each capable of receiving and analyzing reflected signals originating from a single transmitter. Direct communication between the transmitter and each receiver permits the transmitter to know at all times the location, velocity and direction of each receiver thus permitting the receivers to be positioned near the targets relative to the position of the transmitter.

Abstract: In an improved target detector, echo signals received from the same range range bracket on successive scans of the same angular direction are stored. Different combinations of elements from said echo signals are sampled and integrated, each combination being chosen to include elements indicative of a target moving with a particular velocity. Different combinations are indicative of different target velocities, or of targets situated at different initial ranges, and means are provided for signalling an alarm when the integral of any combination exceeds a threshold.

Abstract: This invention relates to a method of and a device for removing range ambiguity in a pulse Doppler radar and to a radar including such a device especially for missile guidance. On tracking operation at a high pulse repetition frequency the method consists in switching the repetition frequency f.sub.R (k) for each time interval .DELTA.t, over a new value f.sub.R (k+1) obtained in a circuit from the measured ambiguous range y(k) and from the ambiguity number n(k), as estimated in a circuit from radar information supplied by the radar, in order to remove eclipsing, to maintain the ambiguity number constant and to estimate the range with a growing accuracy in the course of the tracking operation.

Abstract: A radar system comprising an RF transmitter and receiver means for mounting in a moving carrier for transmitting RF energy and receiving RF energy returns and a non-rotating modulating radar reflector which has a lens means for focusing incident impinging RF energy onto a spot opposite the incident side and a plurality of solid state modulating radar reflectors positioned at the spot locations for selectively reflecting the RF energy and dissipating the RF energy for providing RF energy returns modulated with a lens identification code and frequencies for determining true ground speed, range, glide slope, and azimuth position.

Abstract: This arrangement comprises a fixed frequency emitter circuit (10) for directing a wave (12) to a surface (2) by means of a transmission antenna (11), a receiver circuit (25) for receiving by means of at least one receiving antenna (23) the wave (12) returned by the surface, and a processing circuit (30) for processing the return wave and enabling production of an indication of the velocity. The processing circuit has two branches (50 and 54), a direct branch for applying the received signal to one input of a multiplying member (52), and a delaying branch for applying the received signal to the other input of the multiplying member after having produced a delay t.sub.0 relative to the direct branch. A frequency estimating element (60) receives the multiplying member output signal and a calculation member (62) produces the indication of the velocity from the estimating member output signal and of the distance "h".

Abstract: A ground speed determining radar system for take off roll and landings and roll out maneuvers has a ground based modulating radar reflector and a carrier based radar. The radar transmits microwave energy to the reflector where it is modulated by rotating spaced reflectors and returned to the radar receiver. The receiver is a heterodyne receiver having a log IF stage and a fast time control (FTC) circuit for attenuating clutter and an acquisition loop circuit, lock-on circuit and tracking loop circuit. The acquisition loop circuit includes a center, gate, modulation bandpass filter, switch, acquisition sweep generator and gate generator; the lock-on circuit adds a delay line and a good data indicator to the loop acquisition circuit, and the track loop circuit includes early/late gates, early/late gate low pass filters, subtractor, integrator, the switch and gate generator.

Abstract: A method and apparatus selects the minimum value of a sequence of power measurements taken from each range of a radar's target area. This is preferably performed for two channels of a radar, and the minimum values of both channels for each range are compared to determine the likelihood of a target in each range. Once such likelihood is established, then further processing takes place with regard to ranges with high likelihoods of having targets. The determined minimum value for each range may also be used to normalize each range's power measurements, while preserving phase information, for moving target detection.

Abstract: A method and apparatus provide for the determination of the rate-of-rise of the level of a liquid, such as molten metal in a mold, in a reliable, accurate, and flexible manner. Molten metal passes from a container through an adjustable valve in an orifice to a mold. A microwave generator is connected to a microwave antenna located above the mold for transmitting microwaves to the surface of the molten metal in the mold. A mixer/detector is operatively connected to the antenna, and a computer is operatively connected to the mixer/detector. The computer processes the mixed signal received from the mixer/detector after it is converted to a digital signal. This digital signal is responsive to the Doppler signal caused by change in the level of the metal in the mold. The rate-of-rise of the surface of the molten metal is calculated in response to the digital signal, and is displayed on a monitor.