Showing papers on "Moving target indication published in 1987"

Adaptive airborne MTI: an auxiliary channel approach

Abstract: The suppression of ground clutter returns received by an airborne radar is basically a two-dimensional filtering problem, because the clutter echoes depend on two parameters (velocity, azimuth) instead of velocity only as in case of ground-based radars. This requires two-dimensional sampling (in space and time) of the backscattered echo field, which in practice is fulfilled by a coherent pulse Doppler phased array radar. Previous studies have shown that the space-time clutter covariance matrix of the order NM × NM (N is the number of sensors, M the number of echoes) has only N + M clutter eigenvalues (instead of NM), which means that the signal vector space can be reduced. In the paper an adaptive radar receiver with AMTI (airborne MTI) capability is shown and discussed. It is shown that this AMTI receiver approximates well the theoretical optimum; however, the computational expense is drastically reduced. In view of the dramatic progress in the field of microelectronics and algorithms (e.g. systolic arrays), one can expect that such AMTI receivers will be realisable for real-time applications in the near future.

Frequency domain, pulse compression radar apparatus for eliminating clutter

Abstract: Frequency domain, pulse compression CW (continuous wave) radar apparatus comprises a frequency synthesizer which provides CW signals at a radio frequency, fRF, and at an intermediate frequency, fIF; a linear frequency modulator (LFM) which provides a saw tooth LFM ramp signal having a variable ramp frequency, fLFM, and a mixer for combining the fLFM signal with the fRF signal to thereby provide a CW radar signal having a frequency, (fRF + fLFM). A transmitter is provided for transmitting the CW (fRF + fLFM) radar signal and a receiver is provided for receiving time-delayed CW radar return signals reflected from clutter at a clutter range and reflected from a target at a target range. A second mixer is included for downconverting the time-delayed, clutter and target return signals to the intermediate frequency for processing and a third mixer is provided for extracting the fLFM signal from the time-delayed, intermediate frequency clutter and target return signals to provide, in a frequency-time domain, analog, rectangular wave, clutter and target signals. A time gate and a frequency notch filter are connected for receiving the rectangular wave clutter and target signals, the notch filter having at least one frequency notch for filtering out the rectangular wave clutter signal while passing the rectangular wave target signal when, as is most generally the case, the frequency characteristics of the clutter and target signals are different from one another. A synchronization detector provides in phase (I) and quadrature (Q) components of the target signal and an A/D converter and sampler digitizes and samples the I and Q signal components, the samples being processed in a FFT digital pulse compressor and then in a FFT doppler processor to provide range and doppler cell information.

Sonar system with area moving target indicator

Abstract: A continuous-transmission frequency-modulated (CTFM) scan converted sonar with improved capability for detecting swimmers, miniature submarines and other small intruders in harbors and inlets, and adjacent offshore structures. The system is microprocessor based and menu driven from an operator interactive touch screen. The system utilizes a fast fourier transform (FFT) based frequency analyzer for range discrimination. An area moving target indicator (AMTI) portion of the system cancels echo returns from stationary objects that otherwise mask the echo return of the moving targets. The AMTI causes the system to survey the search area for a number of consecutive scans and store the data. On successive scans, only target information that differs from the stored target map is displayed, thereby reducing clutter caused by surrounding terrain. The AMTI can activate an audio alarm, transmit a serial data alarm message, start a video recorder and annotate the system display to identify the bearing and range of the moving target that has been detected.

A digital signal processor for search radar systems with moving target indication

Abstract: Two digital processor chains, respectively comprising a first chain operating on line upon all radar resolution cells and a second chain operating off line, only upon a few selectable radar cells, are arranged in parallel. With such an arrangement of cir­cuits and logics, modern and sophisticated algorithms can be im­plemented for extracting from the radar video signals a large amount of information about the kind of target and the dynamics of its motion, with a minimum amount of physical circuit components.

Precipitation echo measuring instrument

Abstract: PURPOSE:To enable only a precipitation echo to be accurately displayed by using the data in an area from which the ground echo that can not be completely removed even by the use of a Moving Target Indicator (MTI) filter is not present. CONSTITUTION:Elevation angle judging means 6a judges whether the present elevation angle of an antenna is the one corresponding to an area wherein the ground clutter that can not be completely removed even by a MTI filter is present. Signal analyzing means 6b performs a signal analysis by using the collected data at an elevation angle other than the one at which the ground clutter is present. Data replacing means 6c replaces the data in the area wherein the ground clutter is present with the data after the signal analysis. The ground clutter that can not be completely removed even by the MTI filter is completely removed by using the data of the elevation angle different from that including the ground clutter.

Doppler Frequency Tracking

Abstract: Continuous wave (CW), pulsed Doppler, and moving target indicator (MTI) radars, described in Chapters 13, 14, and 15, respectively, use the Doppler effect to discriminate between moving and stationary objects. These radars provide a method of detecting targets in the presence of ground clutter. Doppler frequency tracking provides clutter rejection that enables continuous range and angle tracking of a single moving target. The single-target tracking mode, in turn, provides the highest data rate and potentially the most accurate measurement of current target position. Although clutter rejection is the most common application, the tracking bandwidths can be narrowed considerably from those used for detection, providing an improvement in the signal-to-noise or signal-to-interference ratio. Since velocity or, more precisely, Doppler frequency is measured directly, predictions of future target position can be made more accurately.