Showing papers on "Moving target indication published in 1990"

A recursive moving-target-indication algorithm for optical image sequences

Abstract: A recursive track-before-detect algorithm, producing potentially large signal-to-noise ratio (SNR) gains under realizable conditions, is described. The basic relation has the form of a linear, constant-coefficient difference equation with a unity magnitude damping factor. Known as recursive moving-target-indication (RMTI), this procedure adapts easily to digital processing and achieves SNR gains comparable to those from other robust track-before-detect algorithms. Examples are given to demonstrate the performance of the moving target indicator (MTI) procedure. >

Adaptive three-dimensional spatio-temporal filtering techniques for infrared clutter suppression

Abstract: The detection of weak targets with an infrared surveillance system is often complicated not only by a severe clutter environment but also by background and platform motion effects. Conventional sequentially applied algorithms combining frame—to—frame registration, clutter rejection filtering, and adaptive thresholding detection simply overwhelm the track processor in a weak target scenario, due to the required lowering of detector block thresholds. To address this problem, we have developed a 3—D filter/"track—before—detect" signal processing approach in which an adaptive spatio—temporal filter is used for clutter suppression and a Viterbi "track—before—detect" block is used for noncoherent target integration. This paper discusses a 3—D adaptive filtering technique which combines time and spatial filtering (in both azimuth and elevation directions) to achieve simultaneous frame—to-frame registration, background clutter suppression, and target preservation/enhancement. In addition, this 3-D filtering procedure whitens the data, thus greatly facilitating the "track-before—detect" processing block task. Unlike other commonly employed procedures, this technique neither entails the suboptimal sequential application of filtering procedures (e.g., spatial followed by temporal filtering) nor demands very accurate subpixel-level registration or exact knowledge of the target's velocity characteristics. The only requirements are that data frames should be roughly aligned (so the offsets are contained within the filter window) and that the assumption of the moving target indicator (MTI) is valid. In this paper simulation results of the 3—D filtering procedure using real, scanned sensor array data are presented, and the procedure performance and implementation complexity are traded off versus adaptive spatial filtering, adaptive temporal, and sequentially applied time/spatial filtering techniques. Also, modification and simulation results are presented for an extension of the 3—D adaptive spatiotemporal filtering technique, which accommodates both MTI and non-MTI case scenarios.

New aspects of airborne MTI

Abstract: The performance of adaptive moving target indication (MTI) filters for use on airborne radar platforms is addressed. Clutter returns received by a moving radar exhibit a Doppler shift which depends on the platform velocity, on the cosine of the angle between the flight axis, and the position of the individual scatterer. Therefore, the platform motion causes clutter echoes to be Doppler broadband, with the bandlimits determined by the platform speed. Efficient clutter suppression requires platform motion compensation or, more general, two-dimensional MTI filters which operate in time and space. In the spatial dimension echo signals may be subject to decorrelation due to the system bandwidth. Such effects are discussed. The results are of particular importance for high-resolution airborne search radar, including real and synthetic aperture applications. >

System and method for simulating targets for a radar receiver utilizing an optical link

Abstract: Both a system and a method for simulating targets for a radar system is disclosed herein which generally comprises a test target generator having an input slaved to the pulse transmit frequencies of the radar system for generating a target simulating signal, a horn antenna for emitting the target simulating signal back to the radar receiver, a laser-operated optical transmission link having a single mode fiber optic cable for transmitting the target simulating signal from the test target generator to the horn antenna via optical carrier, and an amplification and processing circuit system connected between the output of the optical transmission link and the input of the horn antenna for increasing the amplitude of the target simulating signal to a level that is detectable by the radar receiver, and for further processing the signal. The test target generator also generates control signals indicative of a desired amplitude of the resulting target simulating signal, and the system preferably includes a controller in the form of a microprocessor whose input receives the control signal generated by the target generator, and whose output is connected to the amplifier system of the amplification and processing circuit. A phase shift circuit may be included in the processing circuit for both compensating for phase distortions that result from the impedances inherent in the remote transmission of the target simulating signal, and for providing a further means for selectively modifying the signature characteristics of the target simulating signal.

Clutter rejection using multispectral processing

Abstract: The DARPA MUSIC program is presently collecting data to support multi-spectral infrared target detection in clutter.The plan of the MUSIC program is discussed first, followed by the theoretical basis of multi-spectral and recursive moving target indicator (RMTI) processing. An example using data from the MUSIC sensor is presented. In this example spectral-spatial processing of two bands is compared to registration and temporal processing of a singleband.1. INTRODUCTIONThe MUSIC program was initiated in October 1988 to study the application of passive multi-spectral infrared to the detection of air and ground targets. The targets of interest are buried in background clutter and have very weak signal to noise ratios. Interest in using multi-spectral techniques was stimulated by an analysis of multi-spectral datacollected by the NASA Thermal Infrared Multi-Spectral Scanner (TIMS) sensor in Australia in 1985 (Reference 1).This analysis, as well as others, suggested that multi-spectral processing techniques could greatly improve detectionstatistics against targets that are stationary or have little apparent motion relative to a highly cluttered background.In order for multi-spectral processing to be beneficial, the radiance of the target must be proportionately different in

Clutter rejection using connectivity

Abstract: In a FLIR target detection system, true targets (52) are isolated from potential false target indications produced by background clutter through the use of a connectivity algorithm which attempts to find around each potential target (52) a closed path (65) of lower (or higher) intensity without exceeding a predetermined distance from the centroid (64) of the potential target. If the attempt is successful, the potential target (52) is a true target; if not, it is clutter.

Optimal polarimetric detection of radar target in a slowly fluctuating environment of clutter

Abstract: It is shown that in a situation where a radar target is distant enough from the radar and is included in a natural or artificial clutter environment in such a manner that the conventional detection methods fail, it is possible to improve the radar detection performance by using appropriate signal processing on two orthogonal polarization states. A CFAR (constant false alarm rate) polarimetric detection system based on the study of the polarization difference between clutter and target is proposed. Since the polarization state of the clutter echoes fluctuates slowly from cell to cell, an autoregressive model can be applied to the components of the polarization vector to predict the detection thresholds needed to follow the polarization state variation. The detection thresholds are determined to maintain a false alarm probability equal to 10/sup -6/. The presence of a target registers as a significant variation of the estimation error of the polarization vector. Results obtained from measurements of simple and canonical targets with artificial clutter are presented, and these results validate the principle of polarimetric detection. >

Target range detector with moving target indication

Abstract: An apparatus for determining a target position within a selected range segment includes a range gate generator which provides a range gate signal that enables a detector for a time interval corresponding to the range segment and a signal generator, responsive to the range gate signal, which provides a signal having an amplitude which varies with time. The output signal of the signal generator is sampled by a sample and hold circuit. A control signal generator enabled during the range gate interval couples a switching signal to the sample and hold circuit which, upon the reception of a target reflected signal, causes the sample and hold circuit to switch from the sampling mode to the hold mode. The signal amplitude in the hold mode is a representation of the target position within the range gate. Range rate is determined from a knowledge of the elapsed time between range gates corresponding to the same range segment and the difference in positions within the range gates established by the sample and hold circuit when switched to the hold mode upon receptions of the target reflected signals.

Bimodal clutter MTI filter for staggered PRF radars

Abstract: A low-cost, simple adaptive moving target indication (MTI) system for weather and ground clutter rejection is described. The system will be retrofitted into a number of existing staggered PRF radars in order to improve their detection capabilities. The system consists of an adaptive digital MTI filter with complex coefficients, weather clutter map, and clutter parameter estimation unit. The possibility of increasing weather clutter attenuation by the use of a digital MTI filter with complex coefficients has been verified experimentally in the L-band PSR ATC radar AVIA-C, and preliminary experimental results are presented. >

On adaptive implementation of optimum MTI in severely nonhomogeneous environments

Abstract: The problem of achieving the optimum MTI (moving target indicator) detection performance in strong clutter of unknown spectrum when the set of data available for the estimation of clutter statistics is small due to a severely nonhomogeneous environment is studied. A new adaptive implementation, called the Doppler domain localized generalized likelihood ratio processor (DDL-GLR), is proposed, and its detection performance derived. It is shown that the DDL-GLR is a data-efficient implementation of the high-order optimum detector, and that it has several advantages of practical importance over other adaptive processors. >

Clutter rejection limitations from ambiguous range clutter

Abstract: Limitations on achievable clutter rejection due to ambiguous range clutter are described. The profile of clutter power versus range is shown to limit achievable clutter rejection. Ambiguous range effects are discussed in the context of sea clutter, using a model that includes propagation conditions, and rain clutter. Limitations in moving target indication systems are illustrated for sea clutter, where propagation is subject to evaporation ducts. Benefits of fill pulses are illustrated for rain and sea clutter. >

Measurement of the performance of moving target indication radars

Abstract: A quadrahedral reflector that provides ideal moving target Doppler shifted radar returns so that field measurements can determine the actual clutter rejection of the radar has been developed. The development of the measurement technique, results of measurements performed on the US Customs aerostat radar located at Ft. Huachuca, Arizona, and results of measurement on the US Customs aerostat radar located at Marfa, Texas, are described. A typical method for measuring the moving target indication (MTI) improvement factor is to inject synthetic target signals with offset Doppler into the front end of the radar, but this method does not account for transmitter instabilities and scanning losses which could significantly affect the MTI performance. >

Bimodal clutter MTI filter for staggered PRF radars

Abstract: A low-cost, simple adaptive moving target indication (MTI) system for weather and ground clutter rejection is described. The system will be retrofitted into a number of existing staggered PRF radars in order to improve their detection capabilities. The system consists of an adaptive digital MTI filter with complex coefficients, weather clutter map, and clutter parameter estimation unit. The possibility of increasing weather clutter attenuation by the use of a digital MTI filter with complex coefficients has been verified experimentally in the L-band PSR ATC radar AVIA-C, and preliminary experimental results are presented. >

Target distance measuring method and apparatus

Abstract: PURPOSE: To enable the improving of accumulative detection distance with a reduction in searching time by a method wherein a target is irradiated by a necessary time only for the detection of the target with a high repetition frequency in a normal case while the target is irradiated during a period necessary for the detection of a distance of the target in the detection of the target. CONSTITUTION: In a third step 15, as a result of processings in the first and second steps 13 and 14, the detection of a Doppler frequency is performed by a direction of shifting to the fourth step 16 and the Doppler frequency detected is compared with the doppler frequency detected in the step 13. When the target is determined to be identical, operation returns to an original detection phase to continue the processing. When the target is determined to be different, a direction is given to shift to the step 16. In the step 16, a transmission signal 11 is frequency modulated to transmit while the detection of the Doppler frequency is performed with respect to a target reflected signal. Thus, the results are compared with the Doppler frequency detected by a processing of detecting the Doppler frequency in the steps 13 or 15 to determine a distance to the target thereby achieving a so-called FM ranging. COPYRIGHT: (C)1992,JPO&Japio

Effect of leading edge jitter on MTI improvement factor

Abstract: The effect of system disturbances on the improvement factor of moving target indicator (MTI) processors is discussed. The effects are determined analytically and are confirmed by a simulation of a generic MTI processor. The improvement factor for both point and distributed clutter is considered, with distributed clutter placing the more stringent requirements on system stability. Pulse risetime and different statistical models for the disturbances are considered. Equations and curves relating improvement factor to disturbance allow a system analyst to determine the allowable disturbance to achieve a given improvement factor. A useful rule of thumb for the effect of leading edge jitter on improvement factor, reasonably accurate over a wide range of conditions, is given. >

Time domain analysis of ocean clutter in high frequency radar

Abstract: High frequency (HF) radar has the unique potential for over-the-horizon detection of ocean surface targets. However, ocean waves are also strong reflectors for HF radar and ths high clutter level has limited its apphcatlon for target detection. Results from the time domain analysis of ocean clutter show that it can be modelled as two angle modulated signals; the two 'carrier' frequencies correspond to the theoretically predicted 'Bragg' Doppler frequencies. This characterization oocan clutter makes it possible to adapt eXlstlng tlme domain techniques to estimate and, if desired, suppress the clutter signal. Enhanced target detection will be demonstrated.

Digital filter designs for the pre-filter MTI technique with SAR

Abstract: An optimal filter design technique for the prefilter moving target indication (MTI) method used in synthetic aperture radar (SAR) systems is presented. The technique is general, so that the data resampling ratio can be an arbitrary rational number. The digital filters have linear phase and are based on a two-stage design process involving an interpolation and a decimation. A filter is designed for each stage and the final optimized design is the convolution of the single stage filters. The proposed filters are sued when the pulse repetition frequency is a rational multiple of the clutter bandwidth. The filters show good clutter cancellation and minimal aliased overlap between MTI bands. An example is provided which demonstrates the effectiveness of the design technique. >

Effect of leading edge jitter on MTI improvement factor

Abstract: The effect of system disturbances on the improvement factor of moving target indicator (MTI) processors is discussed. The effects are determined analytically and are confirmed by a simulation of a generic MTI processor. The improvement factor for both point and distributed clutter is considered, with distributed clutter placing the more stringent requirements on system stability. Pulse risetime and different statistical models for the disturbances are considered. Equations and curves relating improvement factor to disturbance allow a system analyst to determine the allowable disturbance to achieve a given improvement factor. A useful rule of thumb for the effect of leading edge jitter on improvement factor, reasonably accurate over a wide range of conditions, is given. >

Method for identifying anoprop targets in a pulse radar system

Abstract: In order to identify anoprop targets in pulse radar systems having block-by-block processing and an agile pulse repetition frequency it is proposed to provide the target returns with tags which indicate whether the target report originates from signals from only one pulse repetition frequency, and possibly which, or various pulse repetition frequencies. In the event of a track being formed from the target returns from successive antenna revolutions, an additional check is carried out to determine whether the target returns are based on target detections and different pulse repetition frequencies.