Forward-looking infrared (FLIR) images of targets are characterized by the different target components visible in the image, with are dependent on the target-sensor orientation and target history (i.e., which target components are hot). We define a target class as a set of contiguous target-sensor orientations over which the associated image is relatively invariant, or statistically stationary. Given an image from an unknown target, the objective is proper target-class association (target identity and pose). Our principal contribution is an image classifier in which a distinct set of templates is designed for each image class, with templates linked to the object sub-components, and the associated statistics are characterized via a hidden Markov model. In particular, we employ expansion matching (EXM) filters to identify the presence of the target components in the image, and use a hidden Markov tree (HMT) to characterize the statistics of the correlation of the image with the various templates. We achieve a successful classification rate of 92% on a data set of FLIR vehicle images, compared with 72% for a previously developed wavelet-feature-based HMT technique.

It has been demonstrated that hidden Markov models (HMM) provide an effective architecture for classification of distinct targets from multiple target-sensor orientations. We present a methodology for designing class-based HMM that are well suited to the identification of targets with common physical attributes. This approach provides a means to form associations between existing target classes and data from targets never observed in training. After performing a wavefront-resonance matching-pursuits feature extraction, we present an information theoretic tree-based state-parsing algorithm to define the HMM state structure for each target class. In training, class association is determined by minimizing the statistical divergence between the target under consideration and each existing class, with a new class defined when the target is poorly matched to each existing class The class-based HMM are trained with data from the members of its corresponding class, and tested on previously unobserved data. Results are presented for simulated acoustic scattering data.

Transient scattered fields from a general target are composed of wavefronts, resonances and time delays, with these constituents linked to the target geometry. A classifier applied to transient scattering data requires a statistical model for such fundamental constituents. A Markov model is employed to characterize the transient scattered fields-for a set of target-sensor orientation over which the transient scattering is stationary-utilizing a wavefront, resonance, time-delay "alphabet". The Markov model is utilized in a classifier developed for multi-aspect transient scattering data, with a hidden Markov model (HMM) employed to address the generally non-stationary nature of the multi-aspect waveforms. Each state of the HMM is characteristic of a set of target-sensor orientations for which the scattering statistics are stationary, the statistics of which are characterized via the Markov model. The wavefront, resonance and time-delay features are extracted via a modified matching-pursuits algorithm.

An approach to identifying ground targets from sequential high-range-resolution (HRR) radar signatures is presented. A hidden Markov model (HMM) is employed to model the sequential information contained in multi-aspect target signatures. Dominant range-amplitude features are extracted via RELAX for dimension reduction. A new distance measure is incorporated into the HMM to allow a direct matching operation in the feature domain without requiring interpolation. The approach is applied to the dataset of ten MSTAR targets and is shown to yield an average identification rate of 90.3% using sequential information from 6 degree angular spans.

Biorthogonal wavelets are applied to parse multiaspect transient scattering data in the context of signal classification. A language-based genetic algorithm is used to design wavelet filters that enhance classification performance. The biorthogonal wavelets are implemented via the lifting procedure and the optimization is carried out using a classification-based cost function. Example results are presented for target classification using measured scattering data.

An ultra-wideband (UWB) synthetic aperture radar (SAR) system is investigated for the detection of former bombing ranges, littered by unexploded ordnance (UXO). The objective is detection of a high enough percentage of surface and shallow-buried UXO, with a low enough false-alarm rate, such that a former range can be detected. The physics of UWB SAR scattering is exploited in the context of a hidden Markov model (HMM), which explicitly accounts for the multiple aspects at which a SAR system views a given target. The HMM is trained on computed data, using SAR imagery synthesized via a validated physical-optics solution. The performance of the HMM is demonstrated by performing testing on measured UWB SAR data for many surface and shallow UXO buried in soil in the vicinity of naturally occurring clutter.

Radar scattering from an illuminated object is often highly dependent on the target-sensor orientation. In typical synthetic aperture radar (SAR) imagery, the information in the multi-aspect target signatures is diffused in the image-formation process. In an effort to exploit the aspect dependence of the target signature, the authors employ a sequence of directional filters to the SAR imagery, thereby generating a sequence of subaperture images that recover the directional dependence of the target scattering. The scattering statistics are then used to design a hidden Markov model (HMM), wherein the orientation-dependent scattering statistics are exploited explicitly. This approach fuses information embodied in the orientation-dependent target signature under the assumption that. Both the target identity and orientation are unknown. Performance is assessed by considering the detection of tactical targets concealed in foliage, using measured foliage-penetrating (FOPEN) SAR data.

It is well known that radar scattering from an illuminated object is often highly aspect dependent. We have developed a multiaspect target classification technique for SAR imagery that incorporates matching-pursuits feature extraction from each of a sequence of subaperture images, in conjunction with a hidden Markov model that explicitly incorporates the target-sensor motion represented by the image sequence. This approach exploits the aspect dependence of the signal features to facilitate maximum-likelihood identification. We consider SAR imagery containing targets concealed by foliage.

A wave-based matching-pursuits algorithm is used to parse multi-aspect time-domain backscattering data into its underlying wavefront-resonance constituents, or features. Consequently, the N multi-aspect waveforms under test are mapped into N feature vectors, y/sub n/. Target identification is effected by fusing these N vectors in a maximum-likelihood sense, which we show, under reasonable assumptions, can be implemented via a hidden Markov model (HMM). The algorithm performance is assessed by considering measured acoustic scattering data from five similar submerged elastic targets.

Multiaspect target identification is effected by fusing the features extracted from multiple scattered waveforms; these waveforms are characteristic of viewing the target from a sequence of distinct orientations. Classification is performed in the maximum-likelihood sense, which we show, under reasonable assumptions, can be implemented via a hidden Markov model (HMM). We utilize a continuous-HMM paradigm and compare its performance to its discrete counterpart. The feature parsing is performed via wave-based matched pursuits. Algorithm performance is assessed by considering measured acoustic scattering data from five similar submerged elastic targets.

The subjective tuning of multidimensional systems is considered. Listener preference for certain attributes of sound over others involves multiple options, costs, and payoffs, and may require complex strategies to arrive at an optimal solution. When the complexity of such strategies becomes excessive, listeners adopt simpler strategies that may lead to poor, but achievable, solutions. Active sensory tuning (AST) is aimed at providing the listener an efficient search strategy that yields good solutions within reasonable time bounds. Within an engineering context, AST provides a direct link between the human user and the engineer's design parameters whereby the user can tune the design to their desired goal. This contrasts with much simpler, techniques whereby the user can rank their preference but the engineer must interpret such rankings with respect to the selected parameters.