Infrared (IR) small target detection is a critical technology in both military and civil applications. Nowadays, the optimization-based methods are widely concerned for their good performance under complex backgrounds. However, these optimization models are constructed simply, without sufficient information to fully characterize the features of an image. Moreover, the true target is unprotected in the target weight, and appropriate structural constraints on background are also deficient. Consequently, an IR small target detection algorithm based on target-and-background-weighted two-layer nested model is proposed in this letter. Initially, a two-layer nested model is designed to characterize the global and the local structure of an IR image simultaneously. Then, the smallest eigenvalue of structure tensor (SEoST) is introduced to reweight the overlapping edge information (OEI) map as a target weight, in order to reduce the false alarm rate without missed detection. Furthermore, a weight matrix of background is elaborated as a structural constraint, in order to get a more accurate background estimation result. Finally, the alternating direction multiplier method (ADMM) with a soft-threshold solver is designed to solve the proposed optimization model. Experiments are carried out to evaluate the proposed method by comparing with eight baseline methods, and the results show that the proposed method achieves superior detection performance under complex scenes.

The accurate detection of small infrared (IR) targets in complex backgrounds is crucial for the effective operation of IR search and track (IRST) systems. In this letter, we propose a novel multidirectional diffusion difference measure (MDDDM) approach for accurate and low-complexity IR small target detection. MDDDM consists of three stages. First, a gray intensity measure (GIM) is generated to highlight the important features and suppress high-intensity background regions by using a computationally efficient difference of Gaussian (DoG) filter. Second, the diffusion difference measure (DDM) kernel is computed by fusing an improved Gaussian kernel (IGK) and a directional filter kernel (DFK), utilizing feature minimization instead of omnidirectional gradient judgment to suppress background edge clutters. Finally, threshold segmentation operation is used for precise localization and extraction of the target from the background. Experimental results demonstrate that MDDDM outperforms other state-of-the-art algorithms in terms of detection rate and false alarm rate while maintaining the fastest running speed.

In this work, we analyze the secrecy outage performance of a dual-hop relay system composed of multipleinput- multiple-output radio-frequency (RF) links and a freespace optical (FSO) link while a multiple-antenna eavesdropper wiretaps the confidential information by decoding the received signals from the source node. The channel state information (CSI) of the RF and FSO links is considered to be outdated and imprecise, respectively. We propose four transmit antenna selection (TAS) schemes to enhance the secrecy performance of the considered systems. The secrecy outage performance with different TAS schemes is analyzed and the effects of misalignment and detection technology on the secrecy outage performance of mixed systems are studied. We derive the closed-form expressions for probability density function (PDF) and cumulative distribution function (CDF) over M´alaga channel with imperfect CSI. Then the closed-form expressions for the CDF and PDF of the equivalent signal-to-noise ratio (SNR) at the legitimate receiver over Nakagami-m and M´alaga channels are derived. Furthermore, the bound of the effective secrecy throughput (EST) with different TAS schemes are derived. Besides, the asymptotic results for EST are investigated by exploiting the unfolding of Meijer’s G-function when the electrical SNR of FSO link approaches infinity. Finally, Monte-Carlo simulation results are presented to testify the correctness of the proposed analysis. The results illustrate that outdated CSI shows a strong effect on the secrecy performance of the mixed RF-FSO systems. In addition, increasing the number of antennas at the source cannot significantly enhance the secrecy performance of the considered systems