Effects of polarization and resolution on SAR ATR

Lincoln Laboratory is investigating the detection and classification of stationary ground targets using high resolution, fully polarimetric, synthetic aperture radar (SAR) imagery. A study is summarized in which data collected by the Lincoln Laboratory 33 GHz SAR were used to perform a comprehensive comparison of automatic target recognition (ATR) performance for several polarization/resolution combinations. The Lincoln Laboratory baseline ATR algorithm suite was used, and was optimized for each polarization/resolution case. Both the HH polarization alone and the optimal combination of HH, HV, and VV were evaluated; the resolutions evaluated were 1 ft/spl times/1 ft and 1 m/spl times/1 m. The data set used for this study contained approximately 74 km/sup 2/ of clutter (56 km/sup 2/ of mixed clutter plus 18 km/sup 2/ of highly cultural clutter) and 136 tactical target images (divided equally between tanks and howitzers).     

A relative navigation system for formation flight

A relative navigation system based on both the Inertial Navigation System (INS) and the Global Positioning System (GPS) is developed to support situational awareness during formation flight. The architecture of the system requires an INS/GPS integration across two aircraft via a data link. A fault-tolerant federated filter is used to estimate the relative INS errors based on relative GPS measurements and a range measurement obtained from the data link. The filter is constructed based on a reduced-order model of the relative INS error process. A method for analyzing the filter performance is presented. A case involving two helicopters in formation flight is studied under three different night trajectories to account for the effect of vehicle motion on the INS state transition matrix. The results of the covariance analysis are compared with actual night results over an instrumented test range.     

Distributed decision fusion using empirical estimation

The problem of optimal data fusion in multiple detection systems is studied in the case where training examples are available, but no a priori information is available about the probability distributions of errors committed by the individual detectors. Earlier solutions to this problem require some knowledge of the error distributions of the detectors, for example, either in a parametric form or in a closed analytical form. Here we show that, given a sufficiently large training sample, an optimal fusion rule can be implemented with an arbitrary level of confidence. We first consider the classical cases of Bayesian rule and Neyman-Pearson test for a system of independent detectors. Then we show a general result that any test function with a suitable Lipschitz property can be implemented with arbitrary precision, based on a training sample whose size is a function of the Lipschitz constant, number of parameters, and empirical measures. The general case subsumes the cases of nonindependent and correlated detectors.     

Finite-dimensional filters with nonlinear drift. III: Duncan-Mortensen-Zakai equation with arbitrary initial condition for the linear filtering system and the Benes filtering system

We consider the Duncan-Mortensen-Zakai (DMZ) equation for the Kalman-Bucy filtering system and Benes filtering system. We show that this equation can be solved explicitly with an arbitrary initial condition by solving a system of ordinary differential equations and a Kolmogorov-type equation, Let n be the dimension of state space. We show that we need only n sufficient statistics in order to solve the DMZ equation.     

Finite-dimensional filters with nonlinear drift. V: solution to Kolmogorov equation arising from linear filtering with non-Gaussian initial condition

Despite its usefulness, the Kalman-Bucy filter is not perfect. One of its weaknesses is that it needs a Gaussian assumption on the initial data. Recently Yau and Yau introduced a new direct method to solve the estimation problem for linear filtering with non-Gaussian initial data. They factored the problem into two parts: (1) the on-line solution of a finite system of ordinary differential equations (ODEs), and (2) the off-line calculation of the Kolmogorov equation. Here we derive an explicit closed-form solution of the Kolmogorov equation. We also give some properties and conduct a numerical study of the solution.     

Ulysses observations of latitude gradients in the heliospheric magnetic field: Radial component and variances

The radial component of the magnetic field at Ulysses, over latitudes from –10° to –45° and distances from 5.3 to 3.8 AU, compares very well with corresponding measurements being made by IMP-8 in the ecliptic at 1AU. There is little, if any, evidence of a latitude gradient. Variances in the field, normalized to the square of the field magnitude, show little change with latitude in variations in the magnitude but a large increase in the transverse field variations. The latter are shown to be caused by the presence of large amplitude, long period Alfvénic fluctuations. This identification is based on the close relation between the magnetic field and velocity perturbations including the effect of anisotropy in the solar wind pressure. The waves are propagating outward from the Sun, as in the ecliptic, but variance analysis indicates that the direction of propagation is radial rather than field-aligned. A significant long-period component of 10 hours is present.     

Interplanetary shock waves: Ulysses observations in and out of the ecliptic plane

Between its launch in October 1990 and the end of 1993, approximately 160 fast collisionless shock waves were observed in the solar wind by the Ulysses space probe. During the in-ecliptic part of the mission, to February 1992, the observed shock waves were first caused mainly by solar transient events following the solar maximum and the reorganisation of the large scale coronal fields. With the decay in solar activity, relatively stable Corotating Interaction Regions (CIRs) were observed betwen 3 and 5.4 AU, each associated with at least one forwardreverse shock pair. During the out-of-ecliptic phase of the orbit, from February 1992 onwards, CIRs and shock pairs associated with them continued to dominate the observations. From July 1992, Ulysses encountered the fast solar wind flow from the newly developed southern polar coronal hole, and from May 1993 remained in the unipolar magnetic region associated with this coronal hole. At latitudes beyond 30°, CIRs were associated almost exclusively with reverse shocks only. A comprehensive list of shock waves identified in the magnetic field and solar wind plasma data from Ulysses is given in Table 1. The principal characteristics were determined mainly from the magnetic field data. General considerations concerning the determination of shock characteristics are outlined in the Introduction.     

Ballistic missile track initiation from satellite observations

An algorithm is presented to initiate tracks of a ballistic missile in the initial exoatmospheric phase, using line of sight (LOS) measurements from one or more moving platforms (typically satellites). The major feature of this problem is the poor target motion observability which results in a very ill-conditioned estimation problem. The Gauss-Newton iterative least squares minimization algorithm for estimating the state of a nonlinear deterministic system with nonlinear noisy measurements has been previously applied to the problem of angles-only orbit determination using more than three observations. A major shortcoming of this approach is that convergence of the algorithm depends strongly on the initial guess. By using the more sophisticated Levenberg-Marquardt method in place of the simpler Gauss-Newton algorithm and by developing robust new methods for obtaining the initial guess in both single and multiple satellite scenarios, the above mentioned difficulties have been overcome. In addition, an expression for the Cramer-Rao lower bound (CRLB) on the error covariance matrix of the estimate is derived. We also incorporate additional partial information as an extra pseudomeasurement and determine a modified maximum likelihood (ML) estimate of the target state and the associated bound on the covariance matrix. In most practical situations, probabilistic models of the target altitude and/or speed at the initial point constitute the most useful additional information. Monte Carlo simulation studies on some typical scenarios were performed, and the results indicate that the estimation errors are commensurate with the theoretical lower bounds, thus illustrating that the proposed estimators are efficient     

Dynamic dissipative compensators for multibody flexible spacestructures

The stability characteristics of dynamic dissipative compensators are investigated for multibody flexible space structures having nonlinear dynamics. The problem addressed is that of proving asymptotic stability of dynamic dissipative compensators. The stability proof uses the Lyapunov approach and exploits the inherent passivity of such systems. For such systems these compensators are shown to be robust to parametric uncertainties and unmodeled dynamics. The results are applicable to a large class of structures such as satellites with multiple payloads and space-based manipulators     

C/SiC复合材料超声振动钻孔评估

在分析碳纤维增强碳化硅复合材料的力学性能、密度、孔隙率和弯曲强度的基础上 ,进行了超声钻孔工艺试验 ,检测并研究了材料去除率、孔径差、孔边质量和工具损耗情况 ,得出了超声钻孔是一种好的加工方法的结论。