Marine Target Research Articles

Effects of Breaking Waves on Composite Backscattering from Ship-Ocean Scene**Supported by the National Natural Science Foundation of China under Grant No 61372004, the Fundamental Research Funds for the Central Universities, and the Foundation of Science and Technology on Electromagnetic Scattering Laboratory.

The existence of the sea surface is bound to affect the electromagnetic (EM) scattering from marine targets. When dealing with the composite scattering from targets over a sea surface by applying high-frequency EM theories, the total scattering field can be decomposed into three parts in low sea states, namely, the direct scattering from the sea surface, the direct scattering from targets and the coupling scattering between the sea surface and targets. With regard to high sea states, breaking waves make the direct scattering from the sea surface and the coupling scattering more complicated. To solve this issue, a scattering model is proposed to analyze the composite scattering from a ship over a rough sea surface under high sea states. To consider the effect of breaking waves, a three dimensional geometric model is adopted together with Ufimtsev’s theory of edge waves for the scattering from a breaker. In addition, the coupling scattering between targets and breaking waves is taken into account by considering all possible scattering paths. The simulated results indicate that the influence of breaking waves on the scattering field from the sea surface and on the coupling field is non-negligible, and the numerical results also show the effectiveness of the proposed scattering model.

A Rapid and Efficient Screening Method for Antibacterial Compound-Producing Bacteria.

Antibacterial compounds are widely used in the treatment of human and animal diseases. The overuse of antibiotics has led to a rapid rise in the prevalence of drug-resistant bacteria, making the development of new antibacterial compounds essential. This study focused on developing a fast and easy method for identifying marine bacteria that produce antibiotic compounds. Eight randomly selected marine target bacterial species (Agrococcus terreus, Bacillus algicola, Mesoflavibacter zeaxanthinifaciens, Pseudoalteromonas flavipulchra, P. peptidolytica, P. piscicida, P. rubra, and Zunongwangia atlantica) were tested for production of antibacterial compounds against four strains of test bacteria (B. cereus, B. subtilis, Halomonas smyrnensis, and Vibrio alginolyticus). Colony picking was used as the primary screening method. Clear zones were observed around colonies of P. flavipulchra, P. peptidolytica, P. piscicida, and P. rubra tested against B. cereus, B. subtilis, and H. smyrnensis. The efficiency of colony scraping and broth culture methods for antimicrobial compound extraction was also compared using a disk diffusion assay. P. peptidolytica, P. piscicida, and P. rubra showed antagonistic activity against H. smyrnensis, B. cereus, and B. subtilis, respectively, only in the colony scraping method. Our results show that colony picking and colony scraping are effective, quick, and easy methods of screening for antibacterial compound-producing bacteria.

Cooperative localization of marine targets by UAVs

The paper introduces a cooperative system to search for and localize targets by the use of low cost sensors. The system works based on collaboration of several decentralized, similar and self-organized components that are separately installed on flying vehicles. Interactions and information sharing between these flying vehicles construct a sensor and actuating network that cause the flying vehicles to search more intelligently and gather more efficient signals despite poor quality sensors. In each flying vehicle, a modified version of Monte-Carlo filter is implemented in order to fuse its own sensor measurements with the information received from the other vehicles and the priori of the targets to evolve into the posterior. The target posterior is then used to generate guidance points for the vehicle searching guidance law. The searching guidance law directs the vehicle through guidance points where the best measurements are available for an optimum search. Observability studies are performed to show that the developed system is able to extract the states of targets from measurements. In addition, numerical results by the use of an accurate simulation program, statistically show the performance of the developed system.

A Multi‐Autonomous Underwater Vehicle System for Autonomous Tracking of Marine Life

This paper presents a multi-autonomous underwater vehicle system capable of cooperatively and autonomously tracking and following marine targets (i.e., fish) tagged with an acoustic transmitter. The AUVs have been equipped with stereo-hydrophones that receive signals broadcasted by the acoustic transmitter tags to enable real-time calculation of bearing-to-tag and distance-to-tag measurements. These measurements are shared between AUVs via acoustic modem and fused within each AUV's particle filter for estimating the target's position. The AUVs use a leader/follower multi-AUV control system to enable the AUVs to drive toward the estimated target state by following collision-free paths. Once within the local area of the target, the AUVs circumnavigate the target state until it moves to another area. The system builds on previous work by incorporating a new SmartTag package that can be attached to an individual's dorsal fin. The SmartTag houses a full inertial measurement unit (INU), video logger, acoustic transmitter, and timed release mechanism. After real-time AUV tracking experiments, the SmartTag is recovered. Logged IMU data are fused with logged AUV-obtained acoustic tag measurements within a particle filter to improve state estimation accuracy. This improvement is validated through a series of multi-AUV shark and boat tracking experiments conducted at Santa Catalina Island, California. When compared with previous work that did not use the SmartTag package, results demonstrated a decrease in mean position estimation error of 25–75%, tag orientation estimation errors dropped from 80° to 30° , the sensitivity of mean position error with respect to distance to the tag was less by a factor of 50, and the sensitivity of mean position error with respect to acoustic signal reception frequency to the tag was 25 times less. These statistics demonstrate a large improvement in the system's robustness when the SmartTag package is used.

Mid-infrared imaging system based on polarizers for detecting marine targets covered in sun glint.

When a marine target is detected by a mid-infrared detector on a sunny day, the target's information could be lost if it is located in sun glint. Therefore, we developed a new mid-infrared imaging system capable of effectively detecting marine targets in regions of strong sun glint, which is presented in this report. Firstly, the theory of the analysis methods employed in different detection scenarios is briefly described to establish whether one or two polarizers should be utilized to suppress further the p-polarized component of sun glint. Secondly, for the case in which a second polarizer is employed, the formula for the optimum angle between the two polarizers is given. Then, the results of our field experiment are presented, demonstrating that the developed system can significantly reduce sun glint and can enhance the contrast of target images. A commonly used image processing algorithm proved capable of identifying a target in sun glint, confirming the effectiveness of our proposed mid-infrared polarization imaging system.

Tracking of Range and Azimuth for Continuous Imaging of Marine Target in Monopulse ISAR with Wideband Echoes

Real-time tracking of maneuvering targets is the prerequisite for continuous imaging of moving targets in inverse synthetic aperture radar (ISAR). In this paper, the range and azimuth tracking (RAT) method with wideband radar echoes is first presented for a mechanical scanning monopulse ISAR, which is regarded as the simplest phased array unit due to the two antenna feeds. To relieve the estimation fluctuation and poor robustness of the RAT method with a single snapshot, a modified range and azimuth tracking approach based on centroid algorithm (RATCA) with forgotten factor and multiple echoes is then proposed. The performances of different forgotten factors are investigated. Both theoretical analysis and experimental results demonstrate that RATCA is superior to RAT method. Particularly, when target echo is missing occasionally, RAT method fails while RATCA still keeps good performance. The potential of continuous imaging with shipborne ISAR is verified by experimental results. With minor modification, the method proposed in this paper can be potentially applied in the phased array radar.

Effective coherent integration method for marine target with micromotion via phase differentiation and radon‐Lv's distribution

Effective detection of marine targets with low observability gives a severe challenge to radar signal processing. The micro-Doppler (m-D) signatures of marine target can provide extra information for non-stationary and time-varying signal analysis. Long-time integration is an effective way to strengthen the m-D signal and improve signal-to-clutter ratio. However, the performances are affected by the range across unit and Doppler frequency migration effects. In this study, m-D characteristics of marine target are studied and a novel representation, i.e. phase differentiation and Radon-Lv's distribution (PD-RLVD), is proposed to detect the m-D signal to realise the long-time coherent integration. The PD-RLVD can accurately and directly represent the m-D signal in the chirp rate and chirp change domain appearing as obvious peaks. The proposed method is simple not only because it only requires a 2D Fourier transform of the scaled Radon instantaneous auto-correlation function after PD, but also for not introducing any non-physical attributes. Relations between PD-RLVD and other integration methods are introduced as well. Experiments with real data show that the proposed method can achieve higher integration gain, detection probability, and accuracies of motion parameter estimation.

Sea clutter suppression and micromotion marine target detection via radon‐linear canonical ambiguity function

The micro-Doppler (m-D) signature of a marine target is used for detection within sea clutter in this study. The marine target usually has translational and rotational motions, and the corresponding radar returns can be modelled as a quadratic frequency modulated signal over a period of time. To compensate the range walk and Doppler migration of the micromotion target simultaneously, a novel long-time coherent integration detection algorithm, that is, Radon-linear canonical ambiguity function (RLCAF), is proposed. It has been proved that the m-D signal can be well matched and accumulated in the RLCAF domain using the long-time instantaneous autocorrelation function and associated with the parameterisation of the linear canonical transform. Furthermore, to suppress sea clutter and improve signal-to-clutter ratio, the authors propose a RLCAF spectrum subtraction method using the different properties of RLCAF representations between the target and sea clutter. Finally, experiments with real radar dataset indicate that the proposed method can achieve better integration and detection performance of a marine target with micromotion in case of high sea state.

Experimental verification of maritime target parameter evaluation in forward scatter maritime radar

Maritime security is related to national economic and political interests and is strategically important. One efficient way to accomplish maritime border protection is to use the netted forward scatter radar (FSR). FSR is a special type of bistatic radar that operates in a relatively narrow scattering area along the transmitter–receiver baseline, where the effect of the electromagnetic waves forward scattering on targets is dominant above other scattering mechanisms, and in this case, a forward scatter (FS) cross section may increase by orders of magnitude in comparison with the monostatic radar cross section (RCS). Considered in this study are the major problems of marine forward scattering radar detection and estimation of length of low-profile (small and slow) marine targets using a pre-processing approach. It is based on the assumption that the variation of the phase and amplitude in the Doppler signal signature is stronger inside the FS zone than in an outside region. Two variants of pre-processing algorithms are presented in the study, one for the envelope and the other for the phase. Both variants are based on the use the local variance filtering. The results obtained prove the sufficient improvement in a signal-to-clutter ratio (SCR). Estimation of the marine target length under the low SCR is designed using the assumption of known or previously estimated velocity. Presented results demonstrate high accuracy of length estimation. Considered steps of targets detection and target attributes evaluations are necessary for maritime targets classification. The designed algorithms are verified using a set of experimental records of signals from different marine targets obtained using marine FSR developed by the teams from University of Birmingham, UK and Sofia University, Bulgaria.

Radon-Linear Canonical Ambiguity Function-Based Detection and Estimation Method for Marine Target With Micromotion

Robust and effective detection of a marine target is a challenging task due to the complex sea environment and target's motion. A long-time coherent integration technique is one of the most useful methods for the improvement of radar detection ability, whereas it would easily run into the across range unit (ARU) and Doppler frequency migration (DFM) effects resulting distributed energy in the time and frequency domain. In this paper, the micro-Doppler (m-D) signature of a marine target is employed for detection and modeled as a quadratic frequency-modulated signal. Furthermore, a novel long-time coherent integration method, i.e., Radon-linear canonical ambiguity function (RLCAF), is proposed to detect and estimate the m-D signal without the ARU and DFM effects. The observation values of a micromotion target are first extracted by searching along the moving trajectory. Then these values are carried out with the long-time instantaneous autocorrelation function for reduction of the signal order, and well matched and accumulated in the RLCAF domain using extra three degrees of freedom. It can be verified that the proposed RLCAF can be regarded as a generalization of the popular ambiguity function, fractional Fourier transform, fractional ambiguity function, and Radon-linear canonical transform. Experiments with simulated and real radar data sets indicate that the RLCAF can achieve higher integration gain and detection probability of a marine target in a low signal-to-clutter ratio environment.

Marine target detection in quad-pol synthetic aperture radar imagery based on the relative phase of cross-polarized channels

A focus on marine target detection in noise corrupted fully polarimetric synthetic aperture radar (SAR) is presented. The property of the relative phase between two cross-polar- ized channels reveals that the relative phases evaluated within sea surface area or noise corrupted area are widely spread phase angle region ½−π; π� due to decorrelation effect; however, the rel- ative phases are concentrated to zero and � π for real target and its first-order azimuth ambi- guities (FOAAs), respectively. Exploiting this physical behavior, the reciprocal of the mean square value of the relative phase (RMSRP) is defined as a new parameter for target detection, and the experiments based on fully polarimetric Radarsat-2 SAR images show that the strong noise and the FOAAs can be effectively suppressed in RMSRP image. Meanwhile, validity of the new parameter for target detection is also verified by two typical Radarsat-2 SAR images, in which targets' ambiguities and strong noise are present. © The Authors. Published by SPIE under a Creative Commons Attribution 3.0 Unported License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI. (DOI: 10.1117/1.JRS.9

Australia’s protected area network fails to adequately protect the world’s most threatened marine fishes

In order to maintain ecosystems and biodiversity, Australia has long invested in the development of marine and terrestrial protected area networks. Within this land- and sea-scape, northern Australia represents a global population stronghold for four species of the world’s most threatened marine fish family, the sawfishes (family Pristidae). The distribution of sawfishes across northern Australia has previously only been coarsely estimated, and the adequacy of their representation in protected areas has not been evaluated. The calculated range of each species was intersected with Australia’s marine and terrestrial protected area datasets, and targets of 10% marine and 17% inland range protection were used to determine adequacy of sawfish range protection. Marine targets have been achieved for all species, but the inland range protection targets have not been met for any species. Results indicate that further protection of inland habitats is required in order to improve sawfish protection and habitat connectivity.

Detection and classification of marine targets buried in the sediment using structural acoustic features

We present research on detection and classification of underwater targets buried in a saturated sediment using structural acoustic features. These efforts involve simulations using NRL’s STARS3D structural acoustics code and measurements in the NRL free-field and sediment pool facilities, off the coast of Duck, NC, and off the Coast of Panama City, FL. The measurements in the sediment pool demonstrated RVM classifiers trained using numerical data on two features—target strength correlation and elastic highlight image symmetry. Measurements off the coast of Duck were inconclusive owing to tropical storms resulting in a damaged projector. Extensive measurements were then carried out in 60 ft. of water in the Gulf using BOSS, an autonomous underwater vehicle with 40 receivers on its wings. The target field consisted of nine simulant-filled UXO and two false targets buried in the sediment and twenty proud targets. The AUV collected scattering data during north/south, east/west, and diagonal flights. We discuss the data analyzed so far from which we have extracted 3-D images and acoustic color constructs for 18 of the targets and demonstrated UXO/false target separation using a high dimensional acoustic color feature. Finally, we present related work involving targets buried in non-saturated elastic sediments. [This work is supported by ONR and SERDP.]

The Detection of Marine Ship Target Based on GNSS-R of Stratosphere

Combining with the characteristics of stratosphere platform, this article introduces the marine ship target detection based on GNSS-R technology. The basic working principle is proposed for receiving the signals and detecting the marine targets, mainly from the relationship between geometry, the scattering signal characteristics, the signal reception technologies,subsequent data processing and other aspects of the possible implementation techniques. The detailed reflected signal power calculation is also given out, and calculation results show that the receiver placed on the stratosphere platform can achieve reliable target detection, and verify the feasibility of the stratosphere as a GNSS-R's receiver platform for marine target detection.

Marine Radar Target Detection for USV

Unmanned surface vehicles (USV) have become an intense research area because of their extensive applications. Marine radar is the most important environmental perception sensor for USV. Aiming at the problems of noise jamming, uneven brightness, target lost in marine radar images, and the high-speed USV to the requirement of real-time and reliability, this paper proposes the radar image target detection algorithms which suitable for embedded marine radar target detection system. The smoothing algorithm can adaptive select filter in noise, border and background areas, improves the efficiency and smoothing effect. Based on the iterative threshold, the tolerance coefficient is selected by the histogram, ensures the robust of segmentation algorithm. The location, area and invariant moments features can be extracted from the radar image which after connected-component labeling. The actual radar image processing results demonstrate the effectiveness of the proposed algorithms.

Shocked quartz grains from the Målingen structure, Sweden—Evidence for a twin crater of the Lockne impact structure

AbstractThe Målingen structure in Sweden has for a long time been suspected to be the result of an impact; however, no hard evidence, i.e., shock metamorphic features or traces of the impactor, has so far been presented. Here we show that quartz grains displaying planar deformation features (PDFs) oriented along crystallographic planes typical for shock metamorphism are present in drill core samples from the structure. The shocked material was recovered from basement breccias, below the sediment infill, and the distribution of the orientation of the shock‐produced PDFs indicates that the studied material experienced low shock pressures. Based on our findings, we can exclude that the material is transported from the nearby Lockne impact structure, which means that the Målingen structure is a separate impact structure, the seventh confirmed impact structure in Sweden. Furthermore, sedimentological and biostratigraphic aspects of the deposits that fill the depression at Målingen are very similar to features at the Lockne impact structure. This implies a coeval formation age and thus also the confirmation of the first known marine target doublet impact craters on Earth (i.e., the Lockne–Målingen pair).

Maneuvering Target Detection via Radon-Fractional Fourier Transform-Based Long-Time Coherent Integration

Long-time coherent integration technique is one of the most important methods for the improvement of radar detection ability of a weak maneuvering target, whereas the integration performance may be greatly influenced by the across range unit (ARU) and Doppler frequency migration (DFM) effects. In this paper, a novel representation known as Radon-fractional Fourier transform (RFRFT) is proposed and investigated to solve the above problems simultaneously. It can not only eliminate the effect of DFM by selecting a proper rotation angle but also achieve long-time coherent integration without ARU effect. The RFRFT can be regarded as a special Doppler filter bank composed of filters with different rotation angles, which indicates a generalization of the traditional moving target detection (MTD) and FRFT methods. Some useful properties and the likelihood ratio test detector of RFRFT are derived for maneuvering target detection. Finally, numerical experiments of aerial target and marine target detection are carried out using simulated and real radar datasets. The results demonstrate that for integration gain and detection ability, the proposed method is superior to MTD, FRFT, and Radon-Fourier transform under low signal-to-clutter/noise ratio (SCR/SNR) environments. Moreover, the trajectory of target can be easily obtained via RFRFT as well.

Does Oceania have the institutional capacity to meet marine spatial protection targets under the Convention on Biological Diversity?

The Framework for a Pacific Oceanscape (FPO) catalysed the declaration of large Marine Protected Areas (MPAs) (over 250,000 km) in Oceania. The scale of these Pacific Ocean Arcs’ is designed to address biodiversity loss and climate change that threaten crucial ecological and sociological functions. This paper critically examines the institutional capacity in Oceania to meet spatial marine protection targets under the Convention on Biological Diversity 1992 (CBD). It scrutinises the regional institutions for oceans governance and national institutional arrangements for the oldest and newest Arcs in Kiribati and Palau. Implementation of credible and functional Arcs depends on enforcing the elimination of extractive activities to produce beneficial reserve effects. To meet the 2020 CBD marine spatial protection target will require support from all institutional members and better integration of coastal community governance.

Marine Target Detection from Nonstationary Sea-Clutter Based On Topological Data Analysis

Due to the instinct complexity and the large scale non-stationary of so-called sea-clutter, radar backscatters from ocean surface, it is always challenging to detect the weak marine target. In classical statistical approaches, the seaclutter is modeled as several kinds of stochastic processes, which are found inadequate, especially in high sea-state circumstances. Therefore it is reasonable to discover the underlying dynamics that is responsible for generating the time series of sea-clutter. In this work, we take into account of the marine target detection from the X-Band seaclutter datasets with low Signal-Clutter-Ratio, and propose adequate methods to process these non-stationary data, including Empirical Mode Decomposition and Topological Data Analysis. Both theoretical simulation and experimental results indicate the proposed method's usefulness of for marine target detection, which is implemented by extract different structural features from measured sea-clutter data.

인공어초 조사용 다방향 수중 CCTV 카메라 시스템의 성능 특성

Underwater CCTV camera systems are increasingly replaced the traditional net approach of assessing the species, numbers and aggregation patterns of marine animals distributing around the artificial reefs installed in the inshore fishing grounds, in particular, in relation to the biological investigation of behavior and distribution patterns of target fishes. In relation to these needs, we developed a multi-directional underwater CCTV camera system to use in detecting and tracking marine animals in the artificial reef ground. The marine targets to be investigated were independently tracked by using a camera module toward the bottom and four camera modules installed in the interval of in horizontal plane and inclination of in vertical plane of the CCTV system without the overlap of video frames by each camera module. From the results of several field tests at sea, we believe that the developed multi-directional underwater CCTV camera system will contribute to a better understanding in evaluating the effect of artificial reefs installed in the inshore fishing grounds.