Most of the existing anomaly detection (AD) approaches for hyperspectral images (HSIs) usually achieve high detection accuracy at the cost of high computational complexity. To meet the needs of actual detection scenarios (efficiency, robustness, and accuracy), this letter introduces a fast and robust AD algorithm via subfeatures grouping and binary accumulation (SFBA) for HSIs. We propose a spatial–spectral anomaly scoring strategy to improve detection accuracy. A number of spectral subfeatures of HSI are selected and divided into $N$ groups as the detection input information and the proposed scoring strategy is carried out for $N$ group data, respectively, to improve the detection efficiency. Then binary accumulation is introduced to improve the robustness of AD algorithm by accumulating detection results of each group. Our proposed detection algorithm was compared with the existing algorithms on real hyperspectral datasets, thereby verifying its strong robustness and low computational complexity simultaneously.

For hypersonic flight, high-dynamic plasma sheaths surrounding vehicles deteriorate communication quality. In this work, hypersonic vehicle downlink integrated channels that cascade the plasma sheath channel and Rice fading channel are first established, and the probability density functions (PDFs) of the integrated channel amplitude and phase are derived theoretically. Then, a downlink SIMO system over the integrated channel is considered, including a single antenna transmitter and a single ground receiver equipped with a large number of antennas. For this system, a noncoherent telemetry scheme is proposed, a transmitter that modulates information only in the power of the symbols, and an adaptive maximum likelihood (ML) receiver which demodulates symbols using the PDF of the average received power (ARP) across the antennas. Motivated by the efficient power utilization, an asymptotically optimal constellation design in terms of symbol error rate (SER) with an increasing number of antennas is proposed, under an assumption that CSI statistics are available. The PDF of ARP is well estimated by a reduced reversible jump markov chain monte carlo (RRJ-MCMC) algorithm and used for symbol demodulation and achievable rate derivation. The numerical results demonstrate that the optimal constellation scheme outperforms the amplitude shift keying (ASK) constellation scheme and is robust against the plasma sheath attenuation with moderate antennas or a large line-of-sight (LOS) component.

This study starts from the physical perspective of electromagnetic wave propagation in ionosphere media, and the skywave OTH (over-the-horizon) ionosphere channel model is established for hypersonic vehicles based on the ray-tracing method, and this study identifies the key parameters influencing channel characteristics. Secondly, using the re-entry trajectory of the RAM C-II flight experiment as an example, dynamic multipath channel characteristic parameters—such as loss, delay, and Doppler shift—are analyzed in multiple seasons during the noon and midnight periods at a communication frequency of 14 MHz. The results indicate that the settling effect of the ionosphere at midnight makes the changes in the channel more complex, with the irregular sudden appearance and disappearance of multipath numbers. In addition, channel loss is greater in low-elevation propagation mode than in high-elevation propagation mode, indicating that the channel multipath exhibits high loss and low delay characteristics. The skywave communication channel model for hypersonic vehicles, and the dynamic multipath channel characteristic parameters presented in this study offer valuable support for the design, development, and evaluation of long-distance TT&C (Tracking, Telemetering, and Command) communication systems.

Rapid detection of the new class of hypersonic targets (HTs) presenting unknown military threats in space-based surveillance will guarantee aerospace security. This paper proposes an unsupervised subclass definition and an efficient isolation forest based on an anomalous hyperspectral feature selection (USD-EiForest) algorithm to detect the new class of never-before-seen HTs under emerging hyperspectral sample streams. First, we reveal that the hyperspectral features (HFs) of the new class of HTs have no anomaly characteristics when compared to the globally observed samples while having prominent anomaly characteristics when compared to the subclasses of observed samples. Second, an unsupervised subclass definition method adapted to HTs is utilized to classify the observed samples into several subclasses. Then, an efficient isolation forest is designed to determine whether the data stream sample in each subclass indicates anomaly features that mark the detection of the new class of hypersonic targets (DNHT). Finally, we experiment on the simulated hyperspectral HTs data sets considering the RAM-C II HT as the observed samples and the HTV-2 HT as the unknown samples. The results suggest that the performance of our proposal has competitive advantages in terms of accuracy and detection efficiency.

In hypersonic flight, the coupling mechanisms between the plasma sheath channel and multipath channel are different due to opposite signal transmission directions. As a result, the integrated channel is asymmetric, and the statistical characteristics of the vehicle-to-ground-station (V2G) integrated channel and the ground-station-to-vehicle (G2V) integrated channel vary. In this article, the discrepancies between the two coupling mechanisms of the integrated channels are analyzed, the probability density functions (pdfs) and power spectral density (PSD) functions of the integrated channels are thoroughly derived, and a series of simulations are designed to verify the theoretical derivation results. The results show that the channel asymmetry is mainly reflected in the pdfs of the integrated channel envelopes and that there is no discernible difference between the phase pdfs and PSD functions. Thus, the relevant conclusions can deepen the understanding of the integrated channel of hypersonic vehicles and provide guidance for communication system designs.