Showing papers on "Moving target indication published in 1992"

Linear FMCW radar techniques

Abstract: Frequency modulated continuous wave (FMCW) radar uses a very low probability of intercept waveform, which is also well suited to make good use of simple solid-state transmitters. FMCW is finding applications in such diverse fields as naval tactical navigation radars, smart ammunition sensors and automotive radars. The paper discusses some features of FMCW radar which are not dealt with in much detail in the generally available literature. In particular, it discusses the effects of noise reflected back from the transmitter to the receiver and the application of moving target indication to FMCW radars. Some of the strengths and weaknesses of FMCW radar are considered. The paper describes how the strengths are utilised in some systems and how the weaknesses can be mitigated. It also discusses a modern implementation of a reflected power canceller, which can be used to suppress the leakage between the transmitter and the receiver, a well known problem with continous wave radars.

Application of the multiple PRF technique to resolve Doppler centroid estimation ambiguity for spaceborne SAR

Abstract: The range correlation technique for resolution of Doppler centroid estimation ambiguity for a spaceborne SAR is reviewed. A new technique using multiple pulse repetition frequencies (PRFs) is presented. An algorithm employing simple integer arithmetic for radar systems, such as moving target indicator radar (MTIR) systems, where the PRFs contain a large common divisor, is formulated. For SAR systems, where other performance factors control selection of the PRFs, an algorithm that uses PRFs of arbitrary numerical values is devised to resolve the ambiguity. The performance of this multiple PRF technique is analyzed using a statistical error model. An example is presented for the Shuttle Imaging Radar-C (SIR-C) C-band SAR. >

Target location system

Abstract: A tristatic radar tracking system is disclosed in which two remote transmitters and a radar receiver use a method for combining measurements of the Doppler frequency shift and angle of arrival of two signals scattered by a moving target to derive parameters of the target's trajectory through space.

Unambiguous range-doppler processing method and system

Abstract: Range-Doppler ambiguity is eliminated from an ultra-wideband radar system by transmitting an ultra-wideband chirped pulse towards a moving target, and mixing it with the doppler-shifted chirped pulse which is received as a target echo return signal. Multioctave radar tracing systems can potentiality track stealth aircraft without ambiguity since pulses containing many frequencies can defeat narrow-band radar absorbing material coatings. The unambiguous range-doppler signal processing method mixes the chirped pulse to yield an instantaneous Doppler frequency (which indicates target velocity) and a rate of change in the instantaneous Doppler frequency (which indicates target acceleration).

Total least squares fitting spatiotemporal derivatives to smooth optical flow fields

Abstract: This paper investigates the application of total least squares (TLS) technique in conditioning optical flow field estimates obtained from gradient based optical flow constraints. Optical flow field processing has been applied to perform moving target indication (MTI) for IR/TV sensors but results can be severely degraded in noisy imagery. The usual solution is to apply some form of nonstatistical pre-processing to the input image intensities or statistical post- processing spatial smoothing, such as least squares (LS) fitting, to the output optical flow field vectors to suppress noise. However, LS solution is known for generating biased optical flow field vector estimate in noisy imagery due to spatial gradient matrix noise. Our empirical results show improved performance of TLS over LS at lower SNRs. Results are presented in terms of optical flow field accuracy measures and target detection rates, for synthetic imagery and real infrared imagery.

Radar apparatus provided with a coherent clutter map

Abstract: A radar apparatus provided with transmitter means (1), rotating antenna means (2) and receiver means (3) for the transmission per burst and the processing in a video processor of radar echo signals. The video processor includes moving target detection unit (4) provided with a doppler filter bank, for instance an FFT processor, and slow moving target detection unit (6), provided with coherent clutter maps, one map for each radar transmitter frequency used. The coherent clutter maps are also used for reducing the clutter strength of radar echo signals which are applied to the moving target detection unit (4), by subtracting the coherent clutter strengths stored in the clutter maps from the radar echo signals.

Random-modulation radar signal-induced interference cancellation method and apparatus

Abstract: An uncorrelated clutter noise cancellation method and apparatus employing a measured ambiguity function sample for each randomly-modulated transmission pulse in a randomly-modulated pulsed Doppler radar system. The ambiguity function samples are calculated from a stored copy of the randomly-modulated transmission signal. Estimates of the uncorrelated clutter backscatter are first developed by calculating the amplitude and phase of the radar returns detected in target range and velocity cells corresponding to stationary scatterers. The stationary scatterer contribution to each target cell, computed according to the sample ambiguity function, is then subtracted to eliminate the uncorrelated noise component in the return signal for the target cell. This clutter cancellation technique does not rely on correlations between the randomly-modulated transmission signal and the clutter return signal.

Automatic signal thresholding system

Abstract: An automatic thresholding target detection system operable in high clutter, noisy environments provides target recognition through the generation of automatic signal thresholds. Infrared and radar detectors scanning an environment detect radiant energy from manmade and natural sources. The energy received is converted to electrical signals representative of the varying energy intensities which are filtered and compared with a computed target signal threshold. Signal spikes having amplitudes greater than the automatically generated threshold are then evaluated using a shape parameter test. Finally, an automatic region clutter recognition processor confirms that the spike is a true target, clutter or noise.

Interferometric Ocean Surface Mapping and Moving Object Relocation with a Norden Systems K/sub u/-band Sar

Abstract: United Technologies’ Norden Systems is now fielding a threeaperture interferometric Synthetic Aperture Radar (SAR), flying on a Gulfstream I1 (GII) corporate aircraft. Realtime functions include SAR ground map and enhanced moving target indication (MTI), among others. The MTI function uses interferometric data to compute the Doppler displacement of radially moving targets. Based on that information it overlays symbology at the true target locations on the SAR ground map. Recorded flight data are processed offline to produce interferometric ground maps, displaying intensity and phase information in false color. This paper presents a sampling of results obtained near the Hebrides and Sleat Sound, Scotland, during joint US-UK ocean mapping experiments in July 1991. Examples to be shown will include interferometrically enhanced swells, wind waves and similar features, ship wakes, axd surf breaking along the coastline. Data were collected at ranges of 10 to 50 nm.

Radar target classification system for jet aircraft

Abstract: The target classification system uses the doppler spectrum obtained from te radar echo signals, with suppression of the spectrum components resulting from clutter and the velocity of the radar target, before classification of the target by analysis of periodic, spectral lines within the doppler spectrum, e.g. via a neural network. The analogue radar echo signal is converted into a corresponding digital echo signal, with the time range divided into a number of time increments, each provided with a respective complex sample value, corresponding to an amplitude value. A given number of sample values are grouped in a main block, subjected to Fourier transformation for conversion into the frequency range, each spectrum subjected to removal of clutter and velocity vector components and amplitude normalisation, and the indication vector obtained for the block compared with the indication vectors of known targets.

Dim target detection and clutter rejection using modified high order correlation neural network

Abstract: The authors present a scheme for detecting dim moving targets in highly cluttered background from infrared (IR) data. A high-order spatiotemporal correlation scheme developed by R.J. Liou et al. (1991) to extract the sequency information carried by a target track and reject the background clutter is modified to incorporate target motion dynamics. More than 97% clutter rejection is achieved without losing the target information. In addition, a scoring process is used as a post processor to assign velocity and curvature dependent scores to all the possible target windows. The clutter rejection rate can further be improved by examining the scores of the windows using a back-propagation decision making network. Simulation results are also presented. >

Adaptive clutter suppression for airborne array radars using clutter subspace approximation

Abstract: The main problem is that the moving target echo is submerged in Doppler broadened sidelobe clutter in the frequency domain so that purely temporal filters cannot suppress the sidelobe clutter with the same Doppler frequency as the moving target. However, because the sidelobe clutter comes from different direction from that of the target, the moving target echo can be distinguished from the sidelobe clutter in space domain and from the mainlobe clutter in time (frequency) domain, optimum clutter suppression can be performed by a filter operating on both time and space. The space-time filter requires space-time sampling of the echo field. It can be realized by a coherent pulse Doppler radar with an array antenna. The sensor elements of the array provide spatial samples, and the coherent pulse train realizes temporal sampling of the echo field.

Point target detection in spatially varying clutter

Abstract: The authors develop and analyze high-speed algorithms for the detection of point targets in infrared (IR) images with spatially varying clutter. Current target detection systems are effective in detecting bright targets in a uniform sky, but in areas of strong clutter are either unable to detect targets reliably or are limited by high false alarm rates. The authors assume that target and sensor models are available. Clutter is considered to be poorly characterized and spatially varying. Target detection algorithms are based on filtering to enhance the target signal relative to the background, followed by an adaptive threshold. Statistical analysis of the algorithms is provided to quantify algorithm performance. The system implements a spatially adaptive algorithm that maximizes probability of target detection while maintaining a fixed false alarm rate. The algorithms are robust in the presence of spatially varying clutter. The authors include experimental results to illustrate this. >

Quantization noise spectrum and radar MTI processing

Abstract: The power density spectrum of analog-to-digital (A/D) converter quantization noise is obtained for pulsed and sampled CW radars. While this type of noise is often assumed to be uncorrelated or 'white', it may not be when a small number of quantization levels are occupied by the input signal or the sampling rate (pulse repetition rate) is large compared with the input clutter spectrum bandwidth. The shape of the quantization error spectrum will determine how much of the error noise passes through the low-pass moving target indication (MTI) filter. This shaping of the quantization error spectrum could possible enhance the performance of the MTI processor. Equations describing the quantization noise power density spectrum at the output of an A/D converter are presented, and curves indicating degrees of spectrum whiteness are given. Specific application to MTI radars is addressed. >

Low-altitude target detection by coastline operated marine radar

Abstract: Relevant to a Richian family of fluctuating targets with a composite background of sea-plus-land clutter, the performance prediction of a radar operating in near-coastal regions is elucidated by assuming noncoherent integration of the pulses. Considering the dominance of land clutter, a modified K-distributed statistic is indicated for the overall clutter envelope; and the corresponding probability of false alarm and probability of detection are deduced for fixed threshold detection (s) based on N pulses integrated in the presence of the sea-plus-land clutter and the noise. Even when the target offers a dominant scattered echo, the worst situations of the land clutter affecting the detection performance are indicated. >

Method for the simultaneous determination of the distance and the speed of a target in a radar system

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.

Transient radar for target identification and detection

Abstract: Summary form only given. A radar system using narrow interrogating EM (electromagnetic) pulses can provide target identification and detection capabilities. When a target is illuminated by a narrow EM pulse, the scattered response from the target consists of an early-time response and a late-time response. The late-time response has been utilized to discriminate and identify the target based on the E-pulse (extinction-pulse) and the S-pulse (single-mode extraction pulse) techniques. These techniques are aspect-independent and their basic principles have been developed at Michigan State University. The present effort on these techniques is to study their effectiveness in the presence of sea clutter and noise. >

Motion estimation and compensation in SAR/ISAR imaging

Abstract: The authors present a synthetic aperture radar (SAR) coherent system model and inversion (ISAR) to image a target moving with an unknown constant velocity in a stationary background. It is shown that SAR imaging of a moving target can be converted into imaging the target in a stationary squint-mode SAR problem where the parameters of the squint-mode geometry depend on the target's velocity. A method for estimating the moving target's velocity that utilizes a spatial Doppler analysis of the SAR data within overlapping subapertures is presented. On estimating a moving target's velocity, unlike the temporal Doppler processing methods, the spatial Doppler technique does not require the radar signal to be narrowband. Thus, the reconstructed image's resolution is not sacrificed to improve the target's velocity estimator. >

Radar signal processing device

Abstract: PROBLEM TO BE SOLVED: To suppress generation of false detection by a signal processing device by not performing phase correction of a Doppler frequency even in a region where an unnecessary signal such as weather clutter does nor exist. SOLUTION: The amplitude of a signal from am MTI(Moving Target Indicator) device 4 is detected by an amplitude detection part 6, an output of the amplitude detection part 6 is compared with a noise level 7 in a comparator 8, and it is determined as a clutter exists when the output of the amplitude detection part 6 is larger than the noise level. And against the signal from the MTI device 4, the phase of a Doppler frequency portion estimated at a clutter central frequency estimate part 4 is corrected by a phase correction part 9, and against a signal from the phase correction part 9, a block region is formed a 0 Doppler for filtering by a digital filter 10.

The method to suppress radar clutter by selecting a filter based on production rule using profile of clutter categorized by neural network

Abstract: A method to improve the performance of radar clutter suppression is presented. Generally, a band rejection filter is used for the improvement of SCR (the ratio of signal to clutter). If a fixed band filter is used, the band rejection width and the center frequency of the filter do not match the spectrum of the clutter. A method to solve the mismatch by selecting a filter based on the production rule using the profile of the radar clutter categorized by the neural network is described. The authors' method is validated by computer simulation. A 10-dB improvement factor of SCR is obtained by the method as compared with the conventional pulsed Doppler radar applying MTI (moving target indicator) or adaptive MTI to reject the clutter leakage in coherent integration. >

T-Pulse for Exciting Single Modes of Radar Targets

Abstract: We present an approach called T-pulse approach to excite a single mode of a target. The T-pulse is a time-limited signal that has maximum energy in a given frequency band. While the T-pulse method can be applied to any highly resonant target for the purpose of target identification and discrimination, an application of the T-pulse method to a synthesized thin-wire target is presented to illustrate its ability of exciting single modes.

A novel Doppler processor for search radars

Abstract: A fast adaptive clutter canceller is presented The proposed Doppler processing method is designed for a PRF agile search radar with fast frequency changes and a relatively small number of echoes from a target It compares echo amplitude and instant Doppler frequency of each cell with the surrounding echo characteristics

Radar image display circuit

Abstract: PURPOSE:To improve visibility of a moving target in a clutter area by a method wherein a moving target signal in the clutter area is removed from a normal video signal and the target signal is displayed in the form of a black hole in the clutter area. CONSTITUTION:Timings of a clutter gate signal 1 and a Moving Target Indication (MTI) signal 11 are compared in an AND circuit 2, and when they overlap each other, an MTI gate signal 15 is outputted therefrom. This signal is inputted to a drive circuit 14 and made to be a switching drive signal 16 of a video switch 22. Meanwhile, a normal video signal 17 is divided in two equally and a signal 19a is sent as a normal video signal 28 to a display device 29 via a switch circuit 27. As for the other signal 19b, a video signal 21 is gated to be a signal 23 by the signal 16 in the switch 22, and this signal is sent as a signal 28 to the device 29 via the circuit 27. When the device 29 is made to select the signal 28 and the circuit 27 is made to select the signal 23, a target signal is displayed in the form of a black hole in a clutter signal.

Improved radar detection using adaptive multiband polarization processing

Abstract: Two results concerning clutter estimation are presented. First, the use of frequency diversity improves adaptive detection performance to a greater extent than has been reported for optimum processors under an equal transmit energy constraint. Second, the MPGLR (multiband polarization generalized likelihood ratio) algorithm improves detection performance in the polarization domain and, in contrast to adaptive single-band processing under severely limited observation conditions, can approach the performance of the optimum processor. It is concluded that multiband processing improves performance by increasing the quantity of independent and identically distributed data vectors available for clutter estimation. A means of further improving detection of small targets is presented. This was accomplished by modifying the threshold of the MPGLR test according to the similarity of the maximum likelihood estimate of the target vector to the model assumption. >

Computer simulation study of MTI using FFT and nonlinear processors

Abstract: An analysis of a digital moving target indicator (DMTI) using the traditional fast Fourier transform (FFT) and the recently developed nonlinear spectral estimation techniques is presented. The performance evaluation has been done using simulated target and clutter models in the presence of white Gaussian noise. MTI improvement factor has been computed for all the cases, and it clearly shows the superiority of the nonlinear spectral estimation methods, especially for short data lengths. >

Adaptive signal processing techniques for multiband polarimetric radar

Abstract: The authors present polarimetric detector, the multiband polarization generalized likelihood ratio (MPGLR) test, which provides further performance improvement by the use of the full transmit and receive polarization diversity. The generalized likelihood ratio approach is taken to acquire and adapt to the statistics of the clutter background. In order to obtain a reasonable clutter estimate, with the increased degrees of freedom, sufficient secondary data must be available. However, clutter polarization has been observed to be highly inhomogeneous in range, severely restricting the availability of independent and identically distributed (IID) data vectors necessary for adaptive estimation of the unknown clutter covariance. The use of multiband (frequency diverse) signaling increases the number of IID data vectors available for clutter covariance estimation, and they begin with a discussion of the signaling method. >

Performance of the locally optimum detector in a correlated non-Gaussian disturbance

Abstract: The problem of detecting radar signals embedded in clutter is considered. In radar problems involving weak signal detection conventional space-time processing cannot be used to separate the target from the clutter when the spatial and Doppler spectra of the target and clutter overlap. In such problems the concept of the locally optimum detector (LOD) is useful in coming up with a decision rule to discriminate between the two hypotheses of signal present or signal absent. The clutter which may be correlated can arise from either a non-Gaussian or Gaussian random process. For correlated multivariate student-T distributed clutter it is shown in that significant performance improvements can be obtained with a LOD as opposed to the conventional Gaussian linear receiver. >

Time-frequency analysis of a complex radar signal by a fast recursive processing of the wavelet transform for detection of moving objects in clutters

Abstract: A scheme is proposed for detecting and focusing moving targets in clutter based on a fast recursive wavelet analysis of the received radar signal. The time-frequency formulation provides a powerful tool for obtaining the desired information about the useful signal instantaneous Doppler frequency, which is need for producing a focused image of a target. >

Polarization dependence in ultrawideband impulsive radar target versus clutter discrimination.

Abstract: An account is given of the basic principles of radar polarimetry, and various optimization procedures for the propagation (scattering) range operator equation and the received-power expressions are presented and compared. On the basis of a complete description of isolated and distributed scatterers, polarimetric target classification, target vs clutter discrimination, and optimal polarimetric contrast enhancement algorithms are derived; these should be useful in the interpretation of wideband polarimetric data sets obtained with wideband coherent, dual (orthogonal) polarization channel radar systems.