Shore-based Radar Research Articles

Multichannel Sea Clutter Measurement and Space-Time Characteristics Analysis with L-Band Shore-Based Radar

In order to study the space-time characteristics of sea clutter, the sea clutter is always measured by the airborne multichannel radar; however, the sea clutter shows the heterogeneity between range gates, which means the space-time covariance matrix’s correspondence to the single range gate cannot be estimated accurately. Meanwhile, the measurement of the sea clutter data by the airborne radar is usually affected by the motion of the platform, which makes the analysis results unrepresentative of the space-time characteristics of the pure sea clutter. In this paper, a sea clutter measurement method based on L-band shore-based multichannel radar is proposed, where the transmit sub-array periodically moves with the pulse repetition period to obtain multiple sets of coherent processing interval pulses for each range gate. This measurement method can exclude the influences of the moving platform. Moreover, a sea clutter space-time signal model of the single range gate is proposed, and the model is used to simulate three-dimensional sea clutter data with space-time coupling characteristics. With verification of the measured and simulated data, it can be seen that the data composed of single range gate and multiple coherent processing interval pulses can accurately estimate the space-time covariance matrix corresponding to this single range gate. Furthermore, the space-time characteristics are analyzed based on the measured data. The results show that the eigenvalue spectrum and the spread width of space-time power spectrum are influenced by the backscattering coefficient of sea clutter and the speed of sea surface motion. In comparison, the decorrelation effect caused by the backscattering coefficient of sea clutter is stronger than that caused by the speed of the surface motion. The proposed method is helpful for guiding multichannel sea clutter measurement and the analysis results are of great significance to the clutter suppression algorithms of the marine multichannel radar.

The Dynamic Sea Clutter Simulation of Shore-Based Radar Based on Stokes Waves

The sea clutter model based on the physical sea surface can simulate radar echo at different times and positions and is more suitable for describing dynamic sea clutter than the traditional models based on statistical significance. However, when applying the physical surface model to shore-based radar, the effects of wave nonlinearity, breaking wave, shadow, and radar footprint size must be considered. In this paper, a dynamic sea clutter simulation scheme based on a nonlinear wave is proposed that uses random Stokes waves instead of linear superposition waves to simulate the nonlinear dynamic sea surface and then calculates echo in the form of scattering cells. In this process, the relationship between wind speed and the nonlinear factor of the Stokes wave is derived, a simple model of shadow modulation is provided, and a method for appending the sea clutter spikes formed by breaking waves is developed. The experimental results show that the simulated sea clutter and the real measured clutter have good consistency in intensity, amplitude statistical distribution, Doppler spectrum, and spatiotemporal correlation. The proposed scheme is suitable for the sea clutter simulation of shore-based radar and can also adjust the relevant parameters to extend to other types of sea clutter simulation.

Experimental Study of Maritime Moving Target Detection Using Hitchhiking Bistatic Radar

Hitchhiking bistatic radar system takes the direct wave signal that is transmitted by the non-cooperative radar emitter as the reference to detect and analyze the target echo signal, so as to realize the positioning and tracking of the target. This radar system has the advantages of low cost and strong survivability. Aiming at the problem of passive radar to covert the detection of maritime targets, this paper develops a hitchhiking bistatic radar system for maritime target detection, which uses the shore-based radar as the non-cooperative radar emitter. By continuously collecting the direct wave and target echo data of the non-cooperative radar, the direct wave reference signal reconstruction, pulse compression, interference suppression and synchronization processing, non-coherent integration, MTI (moving target indication), clutter map processing, and adaptive CFAR (constant false alarm rate) detection are completed to obtain the azimuth, bistatic range, and Doppler frequency of the target, and finally realize the positioning of non-cooperative maritime targets. This paper first introduces and demonstrates the composition principle of the system, introduces the signal processing implementation method of the system in detail, and tests and analyzes the key algorithms. The experimental results show that the system can realize the passive coherent detection of maritime moving targets and locate multiple targets at the same time. The experiment obtains a very clear PPI (plane position indicator) display picture of the hitchhiking bistatic radar system, and the radar detection data of the experimental system is in good agreement with the AIS (automatic identification system) data.

Research on sea clutter model of emulating aircraft motion based on shore-based multichannel radar

ABSTRACT Space-time adaptive processing (STAP) is an important clutter suppression technique in airborne multichannel radar. It can be a challenging problem to apply STAP to the maritime airborne radar without knowledge of sea clutter space-time coupling characteristics. The radar sea clutter data with space-time coupling characteristics can be obtained by airborne multichannel radar, but the flight testing is very expensive. A cost-effective technique is presented for emulating airborne motion based on shore-based multichannel radar. The technique is implemented by the same array shared with transmit and receive antenna, where the transmit array uses an inverse displaced phase centre antenna to emulate platform motion and the receive array is used for receiving data. Based on the above technique, a sea clutter model of aircraft motion emulation is proposed. Then, we verify the model by quantitatively comparing the number of eigenvalue and the spread width of the space-time power spectrum between the simulated and measured data. The result shows that the eigenvalue number and the spread width of 3 dB clutter ridge of measured data are more than 79.5% of that belonging to simulated data. It means that the simulated radar sea clutter data generated by this model can better fit the measured data under sea states classes 1–4, which can provide support for the analysis of sea clutter space-time characteristics.

CLASI: Coordinating Innovative Observations and Modeling to Improve Coastal Environmental Prediction Systems

Abstract The Coastal Land–Air–Sea Interaction (CLASI) project aims to develop new “coast-aware” atmospheric boundary and surface layer parameterizations that represent the complex land–sea transition region through innovative observational and numerical modeling studies. The CLASI field effort involves an extensive array of more than 40 land- and ocean-based moorings and towers deployed within varying coastal domains, including sandy, rocky, urban, and mountainous shorelines. Eight Air–Sea Interaction Spar (ASIS) buoys are positioned within the coastal and nearshore zone, the largest and most concentrated deployment of this unique, established measurement platform. Additionally, an array of novel nearshore buoys and a network of land-based surface flux towers are complemented by spatial sampling from aircraft, shore-based radars, drones, and satellites. CLASI also incorporates unique electromagnetic wave (EM) propagation measurements using a coherent array, drone receiver, and a marine radar to understand evaporation duct variability in the coastal zone. The goal of CLASI is to provide a rich dataset for validation of coupled, data assimilating large-eddy simulations (LES) and the Navy’s Coupled Ocean/Atmosphere Mesoscale Prediction System (COAMPS). CLASI observes four distinct coastal regimes within Monterey Bay, California (MB). By coordinating observations with COAMPS and LES simulations, the CLASI efforts will result in enhanced understanding of coastal physical processes and their representation in numerical weather prediction (NWP) models tailored to the coastal transition region. CLASI will also render a rich dataset for model evaluation and testing in support of future improvements to operational forecast models.

Influences of Cross-Sea High-Voltage Transmission Lines on Navigational Aids

With the development of high-voltage electric power industry and the construction of cross-sea transmission projects in coastal ports, the interference of cross-sea high-voltage transmission lines on the performance of ship navigation aids gains considerable attention. The navigation safety control measures for ships crossing the waters of high-voltage transmission lines are proposed to study the navigational safety of the waters for the construction of high-voltage transmission lines across the sea. Conclusions with certain reliability are also drawn based on the analysis of the reasons and mechanisms of the interference phenomenon for the reference of maritime and scientific researchers. The images or signals of interference under the electromagnetic radiation from maritime shore-based radars, shipborne radars, shipborne VHF and GPS equipment through high-voltage transmission lines are obtained through on-site and actual ship testing.

Sea Echoes for Airborne HF/VHF Radar: Mathematical Model and Simulation

Currently, shore-based HF radars are widely used for coastal observations, and airborne radars are utilized for monitoring the ocean with a relatively large coverage offshore. In order to take the advantage of airborne radars, the theoretical mechanism of airborne HF/VHF radar for ocean surface observation has been studied in this paper. First, we describe the ocean surface wave height with the linear and nonlinear parts in a reasonable mathematical form and adopt the small perturbation method (SPM) to compute the HF/VHF radio scattered field induced by the sea surface. Second, the normalized radar cross section (NRCS) of the ocean surface is derived by tackling the field scattered from the random sea as a stochastic process. Third, the NRCS is simulated using the SPM under different sea states, at various radar operating frequencies and incident angles, and then the influences of these factors on radar sea echoes are investigated. At last, a comparison of NRCS using the SPM and the generalized function method (GFM) is done and analyzed. The mathematical model links the sea echoes and the ocean wave height spectrum, and it also offers a theoretical basis for designing a potential airborne HF/VHF radar for ocean surface remote sensing.

A Track Initiation Algorithm Using Residual Threshold for Shore-Based Radar in Heavy Clutter Environments

There is a large error in the actual radar trajectory tracking process. Track initiation is the primary problem in trajectory tracking and the first step in target tracking. The current track initiation algorithms are greatly affected by heavy clutter environments, so it is necessary to propose an algorithm to solve the problem of low track initiation efficiency. This paper presents a track initiation algorithm using a residual threshold in heavy clutter environments. The falling probability of measured value and decision threshold are used to determine the correlation window. The angle limiting condition is added to establish the track association, and the residual threshold is used to further eliminate the false tracks. The initial track experiment with the trajectory data in the sea near Rizhao Port shows that the algorithm is superior to the traditional logic method and Kalman filter method in track quality. The experiment uses the AIS buffer zone to calculate track initiation probability and uses the multi-region AIS trajectory data for verification. The experimental result shows that track initiation probability with the proposed algorithm in this paper can reach 92.31%.

Sea Clutter Amplitude Prediction Using a Long Short-Term Memory Neural Network

In the marine environment, shore-based radars play an important role in military surveillance and sensing. Sea clutter is one of the main factors affecting the performance of shore-based radar. Affected by marine environmental factors and radar parameters, the fluctuation law of sea clutter amplitude is very complicated. In the process of training a sea clutter amplitude prediction model, the traditional method updates the model parameters according to the current input data and the parameters in the current model, and cannot utilize the historical information of sea clutter amplitude. It is only possible to learn the short-term variation characteristics of the sea clutter. In order to learn the long-term variation law of sea clutter, a sea clutter prediction system based on the long short-term memory neural network is proposed. Based on sea clutter data collected by IPIX radar, UHF-band radar and S-band radar, the experimental results show that the mean square error of this prediction system is smaller than the traditional prediction methods. The sea clutter suppression signal is extracted by comparing the predicted sea clutter data with the original sea clutter data. The results show that the proposed sea clutter prediction system has a good effect on sea clutter suppression.

Simulation and analysis system of sea echo based on MATLAB

Marine radar is mainly used for maritime navigation and avoidance of collision. Shore-based marine radar is used for offshore vessel management. In the marine environment, the radar echo is complex for the targets which are polytypic and undulant, and the clutter is strongly and violently affected by the environment. In order to simulate and analyse the sea echo from shore-based radar with real time and high precision, this study sets up a kind of MATLAB simulation and analyses system of real-time data communication and record playback based on transport control protocol/ Internet protocol and GUI. The system can realise the multi-dimensional multi-mode display and subsequent refined simulation of the echo based on static data or dynamic data, and the situation analysis of marine environment is provided through the learning training of multi-frame data. The system has been successfully applied in field experiments and has played an important role in fault analysis and algorithm optimisation, which has very high application value.

Airborne Remote Sensing of Surface Velocities in a Tidal River

The global optimal solution (GOS) has proven to be very accurate for deriving water surface velocities from contemporaneous image pairs, but previous studies have used shore-based radars or satellite measurements with resolutions on the order of a kilometer or tens of meters to establish this. In contrast, the objective of this paper is to derive a GOS velocity field from infrared (IR) (3–5 $\mu \text{m}$ ) images having a 1-m pixel size. Because IR images can frequently exhibit a low signal-to-noise ratio, a newly developed GOS technique with a local similarity metric is used to retrieve velocities from such low-contrast data sets. To demonstrate the utility of this new method, we use airborne data collected in the tidal Potomac River over 11 days and spatially varying flood, ebb, and slack conditions. The resulting GOS-derived velocity estimates are compared against acoustic Doppler current profiler (ADCP) measurements taken simultaneously with the airborne collections. Velocity magnitudes and directions are found to have GOS versus ADCP correlations of 0.93 and 0.99, respectively. This high correlation suggests that the GOS technique may be applicable to a variety of lower contrast imagery that can now be collected by a low-altitude remotely controlled aircraft.

The Utilisation of Pisang Island as a Platform to Support the Current Safety and Security Needs of Marine Navigation in the Straits of Malacca

Current marine navigational practice relies less on long-range visual marine signals such as lighthouses for reference purposes. This is due to the availability of Global Navigation Satellite Systems (GNSS), which are integrated with other navigational aids on ships. Therefore, the objective of this study is to review the function of Pisang Island lighthouse and to propose the most relevant use of Pisang Island for current navigational needs. The function of the lighthouse was reviewed according to the IALA Navigational Guide and the AIS data image. The result showed that the most suitable navigational use of the lighthouse is to act as a reference for Line of Position (LOP). The AIS data image indicated that mariners are not using Pisang Island lighthouse for LOP. The trend in the Straits of Malacca (SoM) was compared with the trend in the Straits of Dover, UK. The selected experts verified that LOP was not practised there. As a specific example, a tanker ship route in the South China Sea was used to further support that LOP was not practised. This evidence supported the view that Pisang Island lighthouse is less relevant for current navigational practice and does not directly support the coastal state VTS operation and the establishment of the marine electronic highway. Furthermore, the existing shore-based VTS radar has limitations on range and the detection of targets near Pisang Island. Therefore, this study proposes the establishment of a new radar station on Pisang Island at the existing site of the lighthouse. The proposed new radar station on Pisang Island will add to the existing coverage of the VTS radar, bridging the coverage gaps to overcome the weakness of the existing shore-based radar and improve the safety and security of marine navigation in the SoM.

Analysis of High‐Frequency EM Scattering Properties on Time‐Varying Sea Surface

This paper proposes to solve the extralarge scale Electromagnetic (EM) scattering problem on a wind-driven sea surface at Low-grazing-angle (LGA) directed against a shore-based radar with an Iterative physical optics (IPO) model. Using Monte Carlo simulations, it compares the average Doppler spectra of backscattered signals at different angles and sea states. The methods are: the forward-backward methodology and its modification with under-relaxation iteration which improves convergence and stability of the IPO; the local iteration methodology and the Fast far-field approximation (FaFFA) in the matrix-vector product which reduce the computational complexity based on the scattering characteristics of sea surface. The simulations show a broadening effect of the Doppler spectra in a more complicated sea state at LGA.

An Accelerated Forward–Backward Iterative Physical Optics for Electromagnetic Scattering from Rough Sea Surface

This article proposes to solve the extra-large-scale (e.g., larger than 1,000 square lambda) electric electromagnetic scattering problem on a wind-driven sea surface at a low grazing angle directed against a shore-based radar with an iterative physical optics model. In order to accelerate the convergence of the iterative physical optics model and improve its robustness, the forward–backward methodology and its modification with under-relaxation iteration are developed first to simulate the rough sea surface scattering. Meanwhile, according to the scattering characteristics of rough sea surface, the local iteration methodology and the fast far-field approximation in the matrix-vector product are proposed to reduce greatly the computational complexity. Through these techniques, this model can solve effectively the extra-large-scale electric scattering problem from the randomly rough sea surfaces.

Erratum to: Ice type extraction of rough ice in the eastern coast of Liaodong Bay with shore-based radar

Erratum to: Ice type extraction of rough ice in the eastern coast of Liaodong Bay with shore-based radar

Ice type extraction of rough ice in the eastern coast of Liaodong Bay with shore-based radar

Sea ice thickness is one of the main hazard factors of ice disasters in Bohai Sea. In this paper, through shore-based radar (X-band) data analysis, the appropriate pixel for ice type extraction was firstly determined. Then, combined with observation data obtained with ice type trackers, the corresponding relationship between radar echo and floating ice type (Nilas ice) in the eastern coast of Liaodong Bay was established and the ice type extraction method based on a specific distance (5 nmi) was proposed. With ice thickness data measured with an icebreaker, we analyzed the errors of extraction results of ice type. The analysis results showed that if only the distance factor was considered, the gray value of shore-based radar echo could be used to extract floating ice type in the eastern coast of Liaodong Bay. The conclusion is of great practical significance to the real-time monitoring of medium-scale sea ice disasters.

Simulation Detection Power of Shore-Based Radar under the Influence of Sea Clutter

According to the principle of electromagnetic wave propagation and the model of radar multipath propagation, this paper established radar detection power model in natural space under the impact of sea clutter, and on condition that conducting simulations to study detection power of shore-based radars on different altitudes and different operating frequencies. Simulation results indicate that when the radar operating frequency is constant, with the erection height increases, the detection range will increase at the same time, while significantly reduced about blind region. When the radar erection height is constant, blind region is filled with radars working at C, S and X operating frequencies. The effect of blind filling is of great importance for adjacent bands. This paper provides theoretical reference analysis for radar detection power assessing and overall with a strong engineering application value.

The Role of Remote Sensing in Predicting and Determining Coastal Storm Impacts

Abstract Storm-induced flooding and other damage present a major problem as the coastal population continues to increase rapidly and sea level keeps rising. To predict the path and landfall of a hurricane or other coastal storm and assess the damage, emergency managers and scientists need continuous information on the storm's path, strength, predicted landfall, and expected damage over large areas. Satellite and airborne remote sensors can provide the required information in a timely and reliable way, as demonstrated by a case study of hurricane Katrina's impact on New Orleans and surrounding areas. Satellite images and hurricane hunter planes were used to track hurricane Katrina, with modelers predicting accurately its path, strength, surge level, and landfall location. Shore-based radars were used to confirm the data as the hurricane approached land. Medium- and high-resolution satellite sensors, helicopters, and aircraft were employed to assess damage to the city, including transportation, power, and c...

Onshore propagation of a buoyant ocean front observed using a shore-based marine radar

An analysis is presented of a 2-h-long time series of X-band marine radar images, collected at Duck, North Carolina (USA), that captured the evolution of a buoyant ocean front as it propagated onshore, following a period of upwelling-favorable winds. In plan view, the front exhibits a scallop-shaped structure similar to that previously observed along strongly convergent fronts. This alongshore structure consists of broad frontal crests (a few hundred meters in length) alternating with sharply angled troughs, or frontal cusps. The evolution of these frontal shapes is explored using a reduced-gravity model (Cooper et al., J. Geophys. Res.-Oceans 106 (2001) 16887) that allows for nonlinear self-interaction of a propagating front. A model simulation shows cusps that develop quickly from initially broad troughs and that point toward the buoyant water, features resembling the observations. However, the simulation also shows a continuous oscillation of frontal shapes, while the observed front reaches a quasi-steady plan form. We attribute this difference in behavior to the gradual shoaling of the observed front as it steadily advances, ultimately reaching water depths of less than 2 m, which is comparable to the thickness of the buoyant layer. As a consequence of the shoaling, we suggest the cusps become sites of enhanced mixing, where water inshore of the front is also accelerated seaward.

A Numerical Model of Internal Wave Refraction in the Strait of Gibraltar

Abstract The relative importance of depth, cross-strait interface till and horizontal current shear upon the wave front shapes of internal waves in the Strait of Gibraltar are examined by means of a numerical refraction model. Results from the model are also compared with observations of wave front shape made in the eastern strait using a shore-based marine radar, which imaged the surface effects of the waves. The model is linear and assumes a time-independent two-layer fluid in which the depth of each layer may be any function of position. The effect of current on the propagation is modeled by the addition of a term in the dispersion relation that increments the phase speed by an amount equal to the current component in the propagation direction, at the depth of maximum internal wave displacement. This current may also be any function of position. The results suggest that in the Strait of Gibraltar, interface tilt and horizontal shear both have a strong influence on the refraction, whereas total depth is...