Shipborne Platform Research Articles

An RD-Domain Virtual Aperture Extension Method for Shipborne HFSWR

High-frequency surface wave radar (HFSWR) is widely used for detecting sea surface or low-altitude targets due to its all-weather operation and over-the-horizon detection capability. To further enhance the maneuverability and detection range of HFSWR, shipborne HFSWR has been developed. However, compared to shore-based platforms, shipborne platforms face challenges such as a small array aperture and reduced Direction of Arrival (DOA) estimation performance due to their limited size. The traditional time–domain virtual aperture extension method, based on the principle of space-time equivalence, aims to improve the array aperture but has limitations when used for HFSWR background or multiple targets with different speeds. To address these issues, this paper proposes a range-Doppler domain (RD-domain) virtual aperture extension method for the uniform linear array, based on the uniform motion model. The contributions of this work include (1) a continuous motion model for shipborne HFSWR, (2) a virtual aperture processing flowchart for shipborne HFSWR, and (3) an RD-domain aperture extension method suitable for HFSWR background or multiple targets with varying speeds. Through simulation and experimental data, we validate the proposed method and analyze its performance.

Sliding window SA-CNN-based CFAR detector for extended target in shipborne HFSWR

ABSTRACT In shipborne high-frequency surface wave radar (HFSWR), the change of platform speed or heading will cause variations in the extension of the Doppler spectrum for vessel targets located in different directions, subsequently resulting in alterations to the signal-to-noise ratio (SNR). These alterations in vessel target echo present challenges for manual parameter adjustments in traditional constant false alarm rate (CFAR) methods for shipborne HFSWR, thereby hindering the maintenance of stable target detection capabilities. In this paper, a self-attention-convolutional neural network (SA-CNN)-based CFAR detector is proposed, which transforms the detection problem into signal structure classification. First, the extension characteristics of vessel target echoes resulting from changes in speed or heading of the shipborne platform are quantitatively analysed, thereby guiding the selection of an optimal sliding window and constructing input vectors for the neural network. Subsequently, the SA-CNN is designed to efficiently extract the structural features of the signal and accurately predict the probability of target presence. Finally, the Monte Carlo method is used to control the false alarm rate effectively. Simulation and real dataset verification demonstrate that the proposed method exhibits superior detection performance compared to traditional methods in shipborne HFSWR, especially for detecting extended targets.

Patent Technology of Shipborne Stabilized Platform

Background: When a ship is sailing or operating at sea, it is unavoidable to produce sixdegrees- of-freedom movements of rolling, pitching, and yawing under the action of sea wind and waves, which seriously impacts the operation of precision equipment on the ship and the safety of personnel. The ship-borne stabilized platform can isolate the ship's motion and eliminate the impact of sea waves on the personnel and equipment on it to a large extent. With the increasing demand for ship surfaces in marine fields, such as navigation equipment, military facilities, and sea condition simulation, there is an urgent need to study ship-borne platforms with high stability and efficiency to isolate swaying and ensure ship performance. Objective: This study aims to analyse the patents and summarize the characteristics and existing problems of the shipborne platform to provide a reference for the future development of the shipborne stabilized platform. Methods: Various representative patents related to shipborne stabilized platforms and multi-DOF platforms were researched in this study. Results: Through the analysis and comparison of patent technology, the main problems existing in the structure and design principle of the existing shipborne stabilized platform are summarized, and the development trend and direction of the shipborne stabilized platform are discussed. Conclusion: Shipborne stabilization is highly significant in isolating the ship's motion. At present, the ship-borne stabilized platform has produced six degrees of freedom of movement, but due to the improvement of control response requirements, the structure of the platform needs to be further improved. With the development of test technology toward intelligent and big data-driven technology, the shipborne stabilized platform is moving toward cloud computing and large-scale testing.

GPS-Free Wireless Precise Positioning System for Automatic Flying and Landing Application of Shipborne Unmanned Aerial Vehicle.

This research is dedicated to developing an automatic landing system for shipborne unmanned aerial vehicles (UAVs) based on wireless precise positioning technology. The application scenario is practical for specific challenging and complex environmental conditions, such as the Global Positioning System (GPS) being disabled during wartime. The primary objective is to establish a precise and real-time dynamic wireless positioning system, ensuring that the UAV can autonomously land on the shipborne platform without relying on GPS. This work addresses several key aspects, including the implementation of an ultra-wideband (UWB) circuit module with a specific antenna design and RF front-end chip to enhance wireless signal reception. These modules play a crucial role in achieving accurate positioning, mitigating the limitations caused by GPS inaccuracy, thereby enhancing the overall performance and reception range of the system. Additionally, the study develops a wireless positioning algorithm to validate the effectiveness of automatic landing on the shipborne platform. The platform's wave vibration is considered to provide a realistic landing system for shipborne UAVs. The UWB modules are practically installed on the shipborne platform, and the UAV and the autonomous three-body vessel are tested simultaneously in the outdoor open water space to verify the functionality, precision, and adaptability of the proposed UAV landing system. Results demonstrate that the UAV can autonomously fly from 200 m, approach, and automatically land on the moving shipborne platform without relying on GPS.

Real Aperture Radar Super-Resolution Imaging for Sea Surface Monitoring Based on a Hybrid Model

In recent years, super-resolution imaging techniques have been intensely introduced to enhance the azimuth resolution of real aperture scanning radar (RASR). However, there is a paucity of research on the subject of sea surface imaging with small incident angles for complex scenarios. This research endeavors to explore super-resolution imaging for sea surface monitoring, with a specific emphasis on grounded or shipborne platforms. To tackle the inescapable interference of sea clutter, it was segregated from the imaging objects and was modeled alongside I/Q channel noise within the maximum likelihood framework, thus mitigating clutter’s impact. Simultaneously, for characterizing the non-stationary regions of the monitoring scene, we harnessed the Markov random field (MRF) model for its two-dimensional (2D) spatial representational capacity, augmented by a quadratic term to bolster outlier resilience. Subsequently, the maximum a posteriori (MAP) criterion was employed to unite the ML function with the statistical model regarding imaging scene. This hybrid model forms the core of our super-resolution methodology. Finally, a fast iterative threshold shrinkage method was applied to solve this objective function, yielding stable estimates of the monitored scene. Through the validation of simulation and real data experiments, the superiority of the proposed approach in recovering the monitoring scenes and clutter suppression has been verified.

Wideband Antennas of Passive Seekers for Anti Radiation Missiles

Suppression of Enemy Air Defence (SEAD) is a fundamental element of Air Power application by means of in protecting friendly air attackers and destroying the enemy’s ability to defend against air attack. Most of the SEAD operation even today relies on Anti-radiation missile (ARM) which is an air-to-surface tactical missile designed to detect, seek, attack and destroy opponent’s radar. Passive seeker of ARM is a miniaturized ESM receiver which is capable of extracting the necessary angular data from the enemy radar emissions. Single head passive seeker covering wide frequency range from L to Ku band is the preferred choice. Wideband antennas have been designed and utilized for Direction Finding applications of ESM/ELINT receivers for ground, air and ship borne platforms. Unlike these platforms, there are several restrictions for passive seeker based compact ESM receiver for missile borne platform specially air to surface missile where lesser diameter is one of the preferred design parameter. This review paper mainly discusses the existing wideband antennas such as spiral, log-periodic, printed circuit vivaldi and all-metal vivaldi antennas and the comparison of their various parameters for passive seeker. The paper also suggests their suitability with respect to their placement on the missile for three configurations: concealed inside the radome, flush-mounted and conformal antenna based. The paper also brought about the specific test facility required for testing and evaluation of passive seeker to characterize it with missile radome which is the most challenging and time consuming task. Among the three passive seeker configuration discussed, conformal antenna based passive seeker using all-metal Vivaldi is the best option avoiding radome aberration correction which is being utilized in the present third generations of ARM. The second commonly and established passive seeker configuration is concealed inside the radome using spiral antennas where handling radome aberration correction is a limitation.

PTESO based robust stabilization control and its application to 3-DOF ship-borne parallel platform

In this paper, a prescribed-time extended state observer (PTESO) is constructed for a three degree-of-freedom (3-DOF) parallel ship-borne platform to estimate the platform’s total disturbances, including dynamic uncertainties, unknown time-varying external disturbances and coupling between the platform motion state variables. The constructed PTESO offers the advantages of converging within a prescribed time, suppressing initial peaking phenomenon and easy implementation. Furthermore, a PTESO based PD-like robust stabilization control law is designed, which maintains the support surface of the platform at a given horizontal position and orientation in the inertial space. Theoretical analyses show that the resulting closed-loop stabilization control system is stable. Simulation results with comparisons are presented to verify the effectiveness of our proposed robust stabilization control strategy.

Imaging VOC distribution and tracing emission sources in surface water by a mobile shipborne spray inlet proton transfer reaction mass spectrometry

Volatile organic compound (VOC) pollution in surface water can affect the growth of microorganisms and even cause damage to human health. Quickly obtaining VOC distribution and tracing emission sources are of great significance to ensure the security of water quality. In this study, we developed a mobile shipborne spray inlet proton transfer reaction mass spectrometry (S-SI-PTR-MS) instrument for rapid and on-line detection of volatile organic compounds (VOCs) in surface water. It mainly consists of a shipborne platform, a spray inlet system, a proton transfer reaction mass spectrometer, and geographic information software (GIS). During the navigation, VOCs in water can be quickly extracted to gaseous state by the SI system and transferred into the proton transfer reaction mass spectrometry (PTR-MS) for detection. The GIS can receive VOC and longitude-latitude data at the same time. And then the identification and concentration information can be shown on an electronic map in real time. The limit of detection and response time were 1.32 μg/L∼9.43 μg/L and 56 s∼114 s, respectively. The spatial resolution is 0.14 m in a common navigation experiment (5 km/h, dwell time=0.1 s), allowing for high-resolution monitoring of VOCs in water. Finally, field experiments were performed on the lower Nanfeihe River and some surfaces of Chaohu Lake in China. During tracing pollution in Nanfeihe River, two VOC emission sources in the downstream were located, nearing a sewage outlet and a wharf, respectively. During imaging VOC distribution in the Chaohu Lake, we found the areas with high-concentration VOCs were mainly along the ship channel. The newly developed S-SI-PTR-MS can monitor water quality in surface water in real time and has the potential to assist environmental protection enforcement.

Composite disturbance observer-based backstepping stabilisation for 3-DOF ship-borne platform with unknown disturbances

ABSTRACT A composite anti-disturbance stabilisation control scheme is presented for the ship-borne platform system with completely unknown disturbances. The completely unknown disturbances consist of external time-varying disturbances and norm-bounded unmodelled dynamics. The composite anti-disturbance control scheme is built through integrating the nonlinear disturbance observer and the robustifying term with the vectorial backstepping technique. The nonlinear disturbance observer is designed to provide the on-line estimations of external time-varying disturbances such that the disturbance compensation term is introduced into the control design. The robustifying term with the adaptive law is employed to attenuate norm-bounded unmodelled dynamics. On the basis of the vectorial backstepping technique, the composite anti-disturbance control law is derived. The composite anti-disturbance control structure consists of the outer layer with the nonlinear disturbance observer for external time-varying disturbance cancellation as well as the inner layer with the vectorial backstepping control together with the robustifying term for unmodelled dynamic attenuation. By means of the Lyapunov stability theory, it is proven that the composite anti-disturbance stabilisation controller can achieve the disturbance rejection and attenuation simultaneously. It is verified by illustrative simulations that the composite anti-disturbance stabilisation control scheme can effectively stabilise the ship-borne stabilisation platform.

Analysis of the Influence of Attitude Error on Underwater Positioning and Its High-Precision Realization Algorithm

GNSS/INS can provide position, attitude, and velocity (PAV) information for shipborne platforms. However, if the ship has a long-term linear motion or a stationary state, and is under the combined actions of sea surface swells, there will be a situation of sideslip and drift; if the ship is traveling slowly or shaking violently, the attitude calculation will not be completed. In the above situation, the traditional single-antenna GNSS/INS measurement mode is not suitable, and the attitude observability is poor; the heading angle attitude information, especially, will gradually diverge. Unreliable information will directly lead to a significant increase in underwater positioning errors. In this paper, a multi-antenna GNSS/INS combination algorithm is developed and used to provide high-precision PAV information, and is thereby able to obtain high-precision underwater positioning results. The experimental results show that the method has improved the acquisition of position and velocity in the horizontal direction and the accuracy of navigation attitude measurement. In particular, the attitude measurement accuracy in the 3 degrees of freedom (DoF) are improved by 10.1% (roll), 8.6% (pitch), and 29.3% (yaw).

Acceleration method of infrared image detail enhancement on FPGA

Among the many cockpit human-computer interaction systems of airborne, vehicle-mounted, and ship-borne platforms, the image detail enhancement technology can improve the ability of personnel to interpret infrared images, which has very important application requirements. The enhanced algorithm running on the embedded computing platform needs to have a higher processing speed and smaller time delay in meeting the needs of real-time interaction. The current infrared video sensor usually has a lower resolution, and the image detail enhancement algorithm still can achieve real-time processing performance on a homogeneous multi-core CPU processing platform. However, as the resolution of platform sensors continues to increase, image processing speed and time delay are difficult to meet application requirements. We propose a method for enhancing and accelerating infrared image details for FPGA platforms. By considering the FPGA's specific domain software and hardware computing architecture, the traditional bilateral filtering image details algorithm is accelerated using local cache and search table, so that real-time processing performance can still be achieved under the input image of the 4k resolution, while almost no additional memory access delay is added. While ensuring the processing effect, the algorithm greatly improves the processing and delay indicators to meet the application requirements of embedded equipment in specific fields such as the cockpit human-computer interaction system.

Simulation analysis of first order sea clutter spectrum for shipborne bistatic HFSWR

Compared with onshore bistatic high frequency surface wave radar (BHFSWR) and shipborne monostatic HFSWR (MHFSWR), shipborne BHFSWR combines the common advantages of both. It is worth noting that the motion state of both mobile stations needs to be considered. In this paper, the spreading characteristics of first-order sea clutter and the doppler shift of the shipborne BHFSWR were analysed theoretically. Then, the simulation results of forward motion and yaw motion are given, and the co-modulation of the echo signal by the motion of the transmitting and the receiving station was investigated. The simulation results show that the amplitude-frequency characteristics of the first-order sea clutter were more complex when the shipborne transmitter and shipborne receiver were at different uniform motion. Finally, combined with the flexibility of shipborne platform, a new scheme was proposed. That is, it can be adjusted the posture information of the shipborne platform, the detection coverage can be better and the spread range of the first-order sea clutter can be reduced.

Coast–Ship Bistatic HF Surface Wave Radar: Simulation Analysis and Experimental Verification

The coast–ship bistatic high-frequency surface wave radar (HFSWR) not only has the anti-interference advantages of the coast-based bistatic HFSWR, but also has the advantages of maneuverability and an extended detection area of the shipborne HFSWR. In this paper, theoretical formulas were derived for the coast–ship bistatic radar, including the first-order sea clutter scattering cross-section and the Doppler frequency shift of moving targets. Then, simulation results of the first-order sea clutter spectrum under different operating conditions were given, and the range of broadening of the first-order sea clutter spectrum and its influence on target detection were investigated. The simulation results show the broadening ranges of the right sea clutter spectrum and left sea clutter spectrum were symmetric when the shipborne platform was anchored, whereas they were asymmetric when the shipborne platform was underway. This asymmetry is primarily a function of platform velocity and radar frequency. Based on experimental data of the coast–ship bistatic HFSWR conducted in 2019, the broadening range of the sea clutter and the target frequency shift were analyzed and compared with simulation results based on the same parameter configuration. The agreement of the measured results with the simulation results verifies the theoretical formulas.

Target characteristics analysis for a shipborne HF surface wave radar

In this study, based on the shipborne high-frequency (HF) surface wave radar target detection application, the first-order ocean surface cross-section for the shipborne HF surface wave radar is simulated, and the relationship between the sea clutter widening characteristics and platform speed is analysed. Then, the relationship between the target echo characteristics of shipborne HF surface wave radar with the platform speed and sails direction is analysed. Finally, combined with the characteristics of the target and sea clutter, a new scheme of target detection for the shipborne radar is proposed. That is, by changing the course of the shipborne platform motion, the target is separated from the widened sea clutter, thereby improving the target-detection performance of the shipborne HF surface wave radar.

The Ozone Water-Land Environmental Transition Study (OWLETS): An Innovative Strategy for Understanding Chesapeake Bay Pollution Events.

Coastal regions have historically represented a significant challenge for air quality investigations due to water-land boundary transition characteristics and a paucity of measurements available over water. Prior studies have identified the formation of high levels of ozone over water bodies, such as the Chesapeake Bay, that can potentially recirculate back over land to significantly impact populated areas. Earth-observing satellites and forecast models face challenges in capturing the coastal transition zone where small-scale meteorological dynamics are complex and large changes in pollutants can occur on very short spatial and temporal scales. An observation strategy is presented to synchronously measure pollutants 'over-land' and 'over-water' to provide a more complete picture of chemical gradients across coastal boundaries for both the needs of state and local environmental management and new remote sensing platforms. Intensive vertical profile information from ozone lidar systems and ozonesondes, obtained at two main sites, one over land and the other over water, are complemented by remote sensing and in-situ observations of air quality from ground-based, airborne (both personned and unpersonned), and shipborne platforms. These observations, coupled with reliable chemical transport simulations, such as the NOAA National Air Quality Forecast Capability (NAQFC), are expected to lead to a more fully characterized and complete land-water interaction observing system that can be used to assess future geostationary air quality instruments, such as the NASA Tropospheric Emissions: Monitoring of Pollution (TEMPO) as well as current low earth orbiting satellites, such as the European Space Agency's Sentinel 5-Precursor (S5-P) with its Tropospheric Monitoring Instrument (TROPOMI).

Using a second-order bistatic cross-section of the ocean surface for bistatic shipborne HFSWR

ABSTRACTThe second-order radar cross section (RCS) of ocean surface is analytically derived for the case in which the radar transmitter is located inland and the receiving antenna is mounted on a shipborne platform. With our previously derived first-order RCS result, the total RCS of ocean surface is simulated for a variety of radar operating parameters and sea states. According to simulation results, it is seen that the relative effect on the second-order spectra due to the platform motion is much smaller than that on the first-order. For the conditions of the radar working with a high operating frequency or a high sea state, the increase of the second-order spectral energy may contaminate the first-order component severely. The obtained results may be useful for setting appropriate limits on the use of radar operating parameters or the bistatic site geometries, from which condition the ocean surface parameters can be effectively extracted from the radar data.

Ionospheric Decontamination for HF Hybrid Sky-Surface Wave Radar on a Shipborne Platform

This letter describes a method of correcting ionospheric frequency modulation for a high-frequency hybrid sky-surface wave radar mounted on a shipborne platform. In the proposed method, azimuth-dependent sea clutter signals are first decomposed into monocomponent signals based on distinguishable differences in their directions of incidence. Afterward, based on the decomposed monocomponent signals, the statistical mean of the time derivatives of the signal phases, weighted by the signal amplitudes, is used to estimate the ionospheric frequency modulation. Finally, the estimated result is applied to the received data to compensate for the ionospheric contamination. Numerical results on simulated data demonstrate the effectiveness of the proposed algorithm.

SATELLITE-DERIVED BATHYMETRY: ACCURACY ASSESSMENT ON DEPTHS DERIVATION ALGORITHM FOR SHALLOW WATER AREA

Abstract. Over the years, the acquisition technique of bathymetric data has evolved from a shipborne platform to airborne and presently, utilising space-borne acquisition. The extensive development of remote sensing technology has brought in the new revolution to the hydrographic surveying. Satellite-Derived Bathymetry (SDB), a space-borne acquisition technique which derives bathymetric data from high-resolution multispectral satellite imagery for various purposes recently considered as a new promising technology in the hydrographic surveying industry. Inspiring by this latest developments, a comprehensive study was initiated by National Hydrographic Centre (NHC) and Universiti Teknologi Malaysia (UTM) to analyse SDB as a means for shallow water area acquisition. By adopting additional adjustment in calibration stage, a marginal improvement discovered on the outcomes from both Stumpf and Lyzenga algorithms where the RMSE values for the derived (predicted) depths were 1.432 meters and 1.728 meters respectively. This paper would deliberate in detail the findings from the study especially on the accuracy level and practicality of SDB over the tropical environmental setting in Malaysia.

Simulation study of first-order sea clutter Doppler spectra for shipborne high frequency radar via hybrid sky-surface wave propagation

The Doppler spectra of first-order sea echo are studied in a high frequency radar system for hybrid sky-surface wave propagation when the receiving antenna array is mounted on a shipborne platform. Here, the platform motion and ionosphere perturbed phases are assumed to be the key factors resulting in the sea clutter spectral fluctuation. Based on the received first-order electric field equation, a closed form of cross sections is derived to account for the ship motion influence. It is shown numerically that the resultant clutter spectra exhibit significant discrepancies with different system operating parameters and platform motion states. In addition, the phase path variations along the inhomogeneous ionosphere are considered by dividing the ionosphere into the quiescent and distorted components. Such manipulation makes it feasible to simulate the phase fluctuations with a method associated with deterministic and stochastic models. Eventually, simulation results for a composite modulation taking account of both effects are provided. Compared with the spread Doppler spectra due to the platform motion, the attached ionosphere perturbed phases will further split and leak the spectral energy, which may bring in difficulties for the applications in remote sensing and target detection.

Nonlinear and Robust Location for Low-cost Shipborne Laser Ranging Positioning

ABSTRACTWithout landing on islands, reefs, or facilities, fast locating targets by the reflectorless ranging integrated with Global Navigation Satellite System (GNSS) has a wide range of application. We propose a nonlinear robust location method and modify current nonlinear estimators for achieving shipborne laser ranging positioning of high precision. The Newton method is recommended as a nonlinear estimator for shipborne ranging positioning since the Gauss–Newton method occasionally fails in critical cases when the control points and the unknown point are approximately coplanar. However, it shows that the vertical positioning based on the shipborne laser ranging is generally of low precision, while the vertical angle measurement is used to further remedy this deficiency. The positioning precision and reliability might be significantly decreased with the increased number of gross errors in the observations that are dynamically implemented on a moving shipborne platform; thus a weighting scheme with high breakdown point is recommended to set the preliminary weights, and then Scheme III of the Institute of Geodesy and Geophysics of China (IGGIII) is applied to iteratively updating the weights of distance observations. It shows that the proposed method based on the angle-distance observational data fusion can be used to achieve a three-dimensional positioning of high precision.