MTI Processing and Weibull-Distributed Ground Clutter

It is shown that the Weibull-distributed ground clutter obeys a Weibull distribution after processing by the double canceler moving target indicator (MTI).     

MTI Clutter Locking for Arbitrary Clutter Spectral Shapes

Clutter-locking criteria for various types of cancellers and clutter spectra are discussed. It is shown that the proper locking criterion for general asymmetric clutter spectra is different from that applicable to those spectra which have even symmetry or are very narrow.     

An Adaptive MTI for Weather Clutter Suppression

A digital realization of an adaptive clutter-locking loop is presented. The purpose of the loop is to estimate the mean Doppler frequency of the clutter. The clutter spectrum is then shifted toward the zero Doppler by this estimate. A fixed moving target indicator (MTI) canceler following the loop suppresses the shifted clutter. Experimental simulations illustrate the feasibility of the loop. Results indicate that the proposed canceler works significantly better than a fixed canceler, while not as well as the 10-pulse moving target detector (MTD) processor. However, the complexity of the MTD is significantly more than the relatively simple adaptive processor presented here.     

Clutter Residues of a Coherent MTI Radar Receiver

In moving target indicator radar receivers a saturation is always present in the IF stages in order to compress the dynamic range of large clutter inputs. This nonlinearity greatly affects the performances of the cancelling circuits, because of the spreading of the spectra. A quantitative analysis of this effect has been conducted, with an analytical expression chosen for the limitation characteristic. A high degradation of both single-and double-canceller improvement factors has been obtained. Losses of 20 dB for the double canceller are not uncommon. Clutter residue levels at the receiver output have also been computed in order to see how the performance compares with ideal constant false alarm rate behavior.     

Effect of timing jitter on performance of MTI filters

The effect of transmitting timing jitter and sampling jitter on a multipulse clutter cancellation system is analyzed, and explicit expressions are obtained for the net increase in the residue clutter power due to timing jitter. The increase in mean-square error is found to be proportional to the jitter variance, with the two jitters contributing almost equally. The system analyzed can have either a recursive or nonrecursive MTI filter, and the latter includes the familiar two- and three-pulse canceller as special cases. The increase in residue clutter power for a three-pulse canceller is about 4.8 dB worse than that for a two-pulse canceller     

The Effect of MTI Filter and Number of Unique Staggers on First-Null Depth and Clutter Attenuation

A recent series of papers have provided a model for a staggered-PRF radar which can be used to estimate both the depth of the first null (which is dependent upon the ratio of some function fM(?) of the set of M sampling deviations {?m} to the average sampling interval) and the clutter attenuation (as a function of the product of fM(?) and clutter standard deviation ?c). Some inconsistencies in the aforementioned papers are discussed and it is shown that realistic filters and typical stagger-ratio sets produce results which differ significantly from the idealized-filter predictions. Furthermore, even after filtering the residual clutter power at dc is shown to be more significant than the power in all the displaced clutter spectra postulated by the aforementioned model.     

Design and Evaluation of an Adaptive MTI Filter

The design and evaluation of an adaptive moving target indicator (MTI) filter, the adaptive canceler for extended clutter (ACEC) is dealt with, taking into consideration adaptivity to clutter mean Doppler frequency. This consideration is one of the most important operational requirements in adaptive MTI's and permits a relatively simple hardware implementation as compared to more general optimization and adaptivity criteria (briefly described). The ACEC's algorithm compensates in real time for the clutter mean Doppler frequency. Performances have been obtained by digital computer simulation in various operational conditions.     

Navigation system design using time-varying complementary filters

A new methodology for the design of navigation systems for autonomous vehicles is introduced. Using simple kinematic relationships, the problem of estimating the velocity and position of an autonomous vehicle is solved by resorting to special bilinear time-varying filters. These are the natural generalization of linear time-invariant complementary filters that are commonly used to properly merge sensor information available at low frequency with that available in the complementary region. Complementary filters lend themselves to frequency domain interpretations that provide valuable insight into the filtering design process. This work extends these properties to the time-varying setting by resorting to the theory of linear differential inclusions and by converting the problem of weighted filter performance analysis into that of determining the feasibility of a related set of linear matrix inequalities (LMIs). Using this set-up, the stability of the resulting filters as well as their "frequency-like" performance can be assessed using efficient numerical analysis tools that borrow from convex optimization techniques. The mathematical background that is required for complementary time-varying filter analysis and design is introduced. Its application to the design of a navigation system that estimates position and velocity of an autonomous vehicle by complementing position information available from GPS with the velocity information provided by a Doppler sonar system is described.     

Battlefield awareness via synergistic SAR and MTI exploitation

“Battlefield awareness” is critical to the success of future military operations. Existing and new sensor platforms will provide the necessary surveillance data; DARPA is developing the systems needed to turn the sensor data into meaningful information for the commanders. A central thrust of these efforts exploits the synergistic relationship between SAR and MTI radar. Used together, they offer comprehensive coverage of the battlefield     

Adaptive backstepping-based flight control system using integral filters

A backstepping control design procedure for uncertain nonlinear flight control system expressible in parameter-strict feedback form is presented in this paper. The proposed backstepping procedure, in association with sliding model control technique, exploits the possibility of avoiding, under certain suitable assumptions, the overparameterization problem existing in the classical backstepping process. In particular, a sliding-model-based integral filter is introduced to facilitate the development of the derivation of the virtual inputs, thus reducing the computational load with regard to the standard backstepping procedure. Moreover, in simulations, the control parameters in the resulted controller are optimally tuned using a genetic algorithm so as to show the full potential of the proposed control system.     

Discrimination Between Log-Normal and Weibull Clutter

Two simple tests are presented for classifying a set of clutter samples into either the log-normal or Weibull distribution. The results obtained by Monte Carlo simulation have shown that both of these tests are only slightly inferior to the test based on the ratio of maximized likelihoods. An application to constant false-alarm rate (CFAR) processing is also discussed.     

Performance Compparison of Optimum and Conventional MTI and Doppler Processors

The performance of an optimum radar signal processor and more conventional techniques (such as MTI, adaptive MTI, and cqherent integration) are compared. A mathematical method is suggested and applied to several cases of practical interest. A number of operative conditions are discovered in which the conventional processing techniques give very poor performance and the optimum radar processor becomes necessary.     

Suboptimal Simulation and Suppression of Clutter Signals

Two digital filters are presented, which are suited for generating (Correlation) or suppressing (decorrelation) by approximation time-discrete signals with preset autocorrelation function from white noise. The advantage of these suboptimal filters is that the determination of their coefficients is very simple. For this reason the filters are weil suited for generating or suppresing signals with rapidly varying statistical parameters. One application possibility is the simulation and the adaptive suppression of clutter signals in surveillance radar systems.     

Weighting Factor and Transmission Time Optimization in Video MTI Radar

In an earlier paper by the author the problem of determining the optimum symmetrical weighting factors for a video MTI radar was discussed. This paper extends this work so as to remove the symmetrical restriction from the problem. In addition, for a staggered pulse system, optimum times of transmission are determined. In the earlier paper a global solution to the restricted optimization problem was achieved. In this paper only a locally optimum solution is achieved for the more general problem.     

Satellite fault diagnosis using a bank of interacting Kalman filters

The main objective of this work is development and testing of a detection, isolation, and diagnosis algorithm based on interacting multiple model (IMM) filters for both partial (soft) and total (hard) reaction wheels faults in a spacecraft. This is shown to be accomplished under a number of different faulty mode scenarios for these actuators associated with the attitude control system (ACS) of a satellite. Various operating and faulty conditions due to changes and anomalies in the temperature, the power supply line voltage, and the loss of effectiveness of the torque and the current are considered in each reaction wheel associated with the three axes of the satellite. Once a fault mode is detected and isolated the recovery procedure can subsequently be engaged by invoking appropriate switching control strategies for the ACS. The application of a bank of interacting multiple Kalman filters for detection and diagnosis of anticipated reaction wheel failures in the ACS is described and developed. Compared with other model-based fault detection, diagnosis and isolation(FDDI) strategies developed in the control systems literature, our FDDI strategy is shown, through extensive numerical simulations, to be more accurate and robust with potential for extension to a number of other application areas.     

Clutter and jammer multipath cancellation in airborne adaptiveradar

Airborne surveillance radars must detect and localize targets in diverse interference environments consisting of ground clutter, conventional jamming, and terrain scattered jammer multipath. Multidimensional adaptive filtering techniques have been proposed to adaptively cancel this interference. However, a detailed analysis that includes the effects of multipath nonstationarity has been elusive. This work addresses the nonstationary nature of the jammer multipath and its impact on clutter cancellation and target localization. It is shown that the weight updating needed to track this interference will also modulate sidelobe signals. At the very least, this complicates the localization of targets. At the worst, it also greatly complicates the rejection of clutter. Several techniques for improving cancellation of jammer multipath and clutter are proposed, including 1) weight vector interpolation, extrapolation, and updating; 2) filter architecture, constraint, and beamspace selection; 3) prefilters; 4) 3-D STAP architectures; and 5) multidimensional sidelobe target editing     

Correlated Clutter and Resultant Properties of Binary Signals

A simple Markov process model of binary, digitized radar clutter returns is assumed. Probability distributions for the number of hits in n observations are developed for small n with a binary parameter describing the process derived for Rayleigh distributed clutter. Tables of distributions are included, along with an example to show the effects of correlation on the false-alarm probabilities of a sliding-window detector.     

Clutter rejection and transmitter-receiver requirements in anairborne radar

Ground clutter rejection requirements imposed on the exciter transmitter-receiver units of multirole airborne radar are examined. Methods are given to determine the characteristics of the units, such as noise, spurious spectral lines level, and analog-to-digital converter (ADC) dynamics, in both high- and medium-pulse-repetition-frequency modes of operation. It is shown that the spectral noise does not depend on either the wave form or the Doppler bandwidth. The reference oscillator spectral noise must be about -155 dB_c/Hz. The level of spurious lines generally depends only on the duty cycle, and the requirement is -80 dB_c for each line. ADC requires 12 to 14 b. The high-frequency mode is the most promising for detecting targets with very low radar cross sections in head-on configuration (free clutter domain)     

Second time around radar return suppression using PRI modulation

A technique for suppressing second-time-around radar returns using pulse-repetition interval (PRI) modulation is presented and analyzed. It is shown that a staggered PRI radar system can offer considerable improvement over a nonstaggered radar system in rejecting second-time-around returns which cause false alarms. This improvement is a function of detector implementation (noncoherent integrator or binary integrator), the number of staggered PRIs, the quiescent false alarm number, the Swerling number of the false return, the transmitted signal power, the second-time-around noise power, and the quiescent noise power of the radar. Small changes in transmitted signal power can be traded off with the quiescent false alarm number to suppress the bogus return significantly. In addition, for a noncoherent integrator, all other parameters being equal, if the second-time-around return is a Swerling case II or IV target, then there is an optimum number of staggered PRIs that can be chosen to minimize the likelihood of its detection. It is also shown that the binary integrator significantly reduces the number of second-time-around return detections when compared with the noncoherent integrator. However, there is an accompanying loss of detection     

Clutter map information for data association and track initialization

This paper considers the problem of forming and maintaining tracks when measurements have both uncertain origin and are corrupted by additive sensor noise. The spatial clutter measurement density is assumed nonhomogeneous and known. The PPDA-MAP algorithm provides a set of recursive formulae for data association and probability of target existence, thus enabling automatic track initiation, track maintenance, and track termination. New values for initial probability of target existence for IPDA-type algorithm are also derived. Simulation results compare the performance of IPDA-MAP with IPDA, IMM-PDA, IMM-PDA-MAP, EB-PDA and EB-PDA-MAP in a heavy and nonuniform clutter situation.