Collaborative Representation-Based Binary Hypothesis Model with Multi-features Learning for Target Detection in Hyperspectral Imagery

In this paper we present a new methodology for automated target detection and identification in hyperspectral imagery. The standard paradigm for target detection in hyperspectral imagery is to run a detection algorithm, typically statistical in nature, and visually inspect each high-scoring pixel to decide whether it is a true detection or a false alarm. Detection filters have constant false alarm rates (CFARs) approaching 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-5</sup> , but these can still result in a large number of false alarms given multiple images and a large number of target materials. Here we introduce a new methodology for target detection and identification in hyperspectral imagery in conjunction with a data-driven target detection algorithm that shows promise for hard targets. The result is a greatly reduced false alarm rate and a practical methodology for aiding an analyst in quantitatively evaluating detected pixels.

Kernel-based regularized-angle spectral matching for target detection in hyperspectral imagery

Metric learning-based methods, which yield great performance and show considerable potential to improve the performance of hyperspectral image processing, aim to calculate the Mahalanobis distance metric matrix. In this article, we proposed a symmetric information-theoretic metric learning (SITML) method for hyperspectral target detection. The SITML algorithm is designed based on the classical information-theoretic metric learning (ITML) and, minimizes the differential Kullback–Leibler (KL) divergence. To enhance both of the detection performance and the generalization ability, we build metric spaces from the neighborhood of training samples to preserve the local discriminative information. Then, we conduct local pairwise constraints to maximize the Jeffery divergence (also named the symmetric KL divergence) of two multivariate Gaussian distributions to solve the problem of an asymmetric KL divergence. Finally, we use a closed-form solution to solve the optimization problem. Intensive experiments on three hyperspectral datasets indicate that SITML outperforms the classical ITML algorithm and other state-of-the-art target detection methods.

Although sparse representation based classification (SRC) has gained great success, doubts on the necessity of sparse constraint come in recent years. And collaborative representation based classification (CRC) has attracted much attention from researchers in fields of signal processing, image processing and pattern recognition. In this paper, an algorithm called collaborative dictionary learning with structured incoherence (CDLSI) is proposed for collaborative representation based detection (CRD), which can be viewed as a binary classification problem, in hyperspectral imagery (HSI). An inter-class incoherence term is added to make sub-dictionaries to be as independent as possible. During the optimizing procedure, sub-dictionaries are updated atoms-by-atoms with metaface method. Specifically, considering the non-sparse representation of CRC, the coefficients are iteratively optimized with l₂ -norm regularization during the coding procedure in CDLSI. Once the sub-dictionaries are obtained, the collaborative representation based technique is then used for detection. The proposed algorithm is applied to several real hyperspectral images for detection. Experimental results confirm the effectiveness of the proposed approach, and prove the superiority to the traditional algorithms.

Orthogonal subspace projection (OSP) has been used in hyperspectral image processing for automatic target detection and image classification. Existing OSP based approaches for target detection require a priori knowledge of all undesired signatures present in the input scene. In this paper, we proposed a new technique for target detection which does not require a priori knowledge of the non-target signatures present in the input scene. The length of any pixel vector containing the target reduces significantly when it is projected in a direction orthogonal to the target signature. Thus the ratio between the original pixel vector to the projected pixel vector yields a high value for the pixels containing the target. Therefore, an OSP based parameter along with noise adjusted principal component analysis (NAPCA) was introduced in this paper for target detection in hyperspectral images. For noisy images, NAPCA is used as a preprocessing step to reduce the effects of noise as well as to reduce the spectral dimension thereby yielding better target detection capability while enhancing the computational efficiency. For noise-free input scenes or when very small amount of noise is present in the input scene, principal component analysis (PCA) may be used instead of NAPCA. The OSP based technique requires that the number of spectrally distinct signatures present in the input scene must be less than the number of spectral bands. The proposed algorithm yields very good results even when this criterion is not satisfied.

Target detection in hyperspectral imagery is a complex process due to many factors. Exploiting the hyperspectral image for analysis is very challenging due to large information and low spatial resolution. However, hyperspectral target detection has numerous applications. Hence, it is important to pursue research in target detection. In this paper, a literature survey of target detection algorithms for hyperspectral imagery is presented along with scope for future research. An overview of theory behind the hyperspectral imaging is detailed. Also, various challenges involved in exploring the hyperspectral data are discussed.

This paper introduces Cointegration Theory to address the problem of adaptive target detection in hyperspectral imagery. Cointegration Theory aims at mining a long-term equilibrium relationship, which refers to the condition that an appropriate linear combination of several non-stationary series can be stationary as long as they have similar or related drift. Hyperspectral response sequences, which are highly non-stationary, have similar patterns among the same materials. To be treated as a time series, each given hyperspectral curve is matched with the reference spectrum via the Johansen Cointegration Test. The statistic of the test is then used for target detection. Experimental results indicate that our proposed method is effective and has a strong capacity to identify interesting objects from their background.

Unstructured detectors such as KGLRT, ACE and AMF are widely applied for target detection in hyperspectral imagery (HSI). However, conventional global and local approaches construct background model without considering the contamination caused by anomalies and suspected targets. This paper proposes a local ACE algorithm based on the minimum covariance determinant (MCD) estimator. In the proposed algo-rithm, a spectral angle based clustering method is applied to the whitened hyperspectral data to form several disjoint clusters over the whole image. Then for each cluster, the robust estimations of its background statistics are obtained using the MCD estimator. Finally, the ACE detector is applied to each pixel utilizing the robust background statistics of the cluster. With experimental results on two different real datasets, the superiority of the proposed algorithm is demonstrated.

Subpixel target detection in hyperspectral imagery is challenging since subpixel targets are smaller in size than the resolution of a single pixel and accurate pixel-level labels on subpixel targets are often unavailable. In particular, this article addresses the problem of learning a prime prototype target signature from imprecisely labeled highly mixed hyperspectral data. Two algorithms, multiple-instance subpixel adaptive cosine estimator (MI-SPACE) and multiple-instance subpixel spectral matched filter (MI-SPSMF), based on multiple-instance learning framework are presented. The proposed methods aim to learn a discriminative prime target signature by maximizing the posterior detection statistics of subpixel hyperspectral targets for the correspondingly proposed subpixel adaptive cosine estimator (SPACE) and subpixel spectral matched filter (SPSMF) detectors, which are also developed in this article. Experimental results demonstrate the effectiveness of the proposed methods on both simulated and real-field hyperspectral subpixel target detection tasks.

Sparse representation based on stacked kernel for target detection in hyperspectral imagery

The processing chain leading to specific material detection in hyperspectral imagery implies the use of atmospherically corrected images of emissivity or reflectance before comparing image signatures to a database of materials' signatures. This is a sensible approach for the reflective hyperspectral bands l and when the pixels are completely filled with a uniform material in the LWIR bands (8 to 12 microns). In the LWIR, the atmospheric correction process is different of what is used in the reflective bands and involves the use of a temperature and emissivity separation process (TES). If the pixel is not filled with a uniform material and the measured radiance is produced from the mix of materials having different emissivity and temperatures, the output of the TES will not be linear in temperature and in emissivity and will be contaminated by the non-linear mix of the temperature and emissivity of the materials leading to a potential for confusion during the detection process. In this paper, we propose a detection approach using the ground leaving radiance that is used directly to perform detection using emissivity signatures contained in a database. The detection results using this process are compared with the detection results using the output of a TES algorithm. The study is performed in simulation without noise and with the exact knowledge of the downwelling irradiance. The results show that a detection algorithm using the ground leaving radiance performs better than its counterpart using the emissivity when the difference in temperature increases.

Reduction of the potential health risks to consumers caused by food-borne infections is a very important food safety issue of public concern; one of the leading causes of food-borne illnesses is fecal contamination. We consider detecting fecal contaminants on chicken carcasses using hyperspectral imagery. We introduce our new improved floating forward selection (IFFS) algorithm for feature selection of the wavebands to use in hyperspectral data for classification. Our IFFS algorithm is an improvement on the state-of-the-art sequential floating forward selection (SFFS) algorithm. Our initial results indicate that our method gives an excellent detection rate and performs better than other quasi-optimal feature selection algorithms.

Non-overlapping classification of hyperspectral imagery with superpixel segmentation

In this paper we examine the efficacy of using the closest distance to center algorithm in conjunction with ellipsoidal multivariate trimming (MVT) to find outliers in a hyperspectral image. MVT is applied here as a global anomaly detector on images that are pre-processed into clusters using a technique called X-means. Under the assumption that there are no more than 5% outliers in any given cluster set, we develop a method, based upon principal component analysis pre-processing, to create a flexible threshold for determining the percentage of data to retain with MVT. Using a retention percentage that more adequately reflects the actual number of outlier-free observations allows one to form estimates of the mean and covariance matrix that more effectively decrease the effects of swamping and masking as compared to using a set percentile for retention. These ideas are tested against real and synthetically generated hyperspectral imagery.

In this paper, collaborative representation is proposed for anomaly detection in hyperspectral imagery. The algorithm is directly based on the concept that each pixel in background can be approximately represented by its spatial neighborhoods, while anomalies cannot. The representation is assumed to be the linear combination of neighboring pixels, and the collaboration of representation is reinforced by l <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> -norm minimization of the representation weight vector. To adjust the contribution of each neighboring pixel, a distance-weighted regularization matrix is included in the optimization problem, which has a simple and closed-form solution. By imposing the sum-to-one constraint to the weight vector, the stability of the solution can be enhanced. The major advantage of the proposed algorithm is the capability of adaptively modeling the background even when anomalous pixels are involved. A kernel extension of the proposed approach is also studied. Experimental results indicate that our proposed detector may outperform the traditional detection methods such as the classic Reed-Xiaoli (RX) algorithm, the kernel RX algorithm, and the state-of-the-art robust principal component analysis based and sparse-representation-based anomaly detectors, with low computational cost.