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The object detection based on video has the problem of poor recognition effect in bad weather, so it is necessary to make up for video defects and improve the robustness of detection framework. In view of this problem, this study designs an object detection framework based on radar and video fusion. YOLOv5 (You Only Look Once version 5) network is used to obtain image feature map and image detection frame, density-based clustering is used to obtain radar detection frame, and radar data is encoded to get object detection results based on radar information. Finally, the detection boxes of the two are superimposed to obtain a new ROI (Region of Interest), and the classification vector after fusion radar information is obtained, which improves the detection accuracy in extreme weather. The experimental results show that the mAP(mean Average Precision) of the framework reaches 60.07%, and the parameter number is only 7.64 x 10°, which indicates that the framework has the characteristics of lightweight, fast computing speed and high robustness, and can be widely used in embedded and mobile platforms. [ABSTRACT FROM AUTHOR]

Aiming at the current situation of lack of environment and equipment in radar training, a radar operation training method based on the combination of virtual and real is proposed. Firstly, the connotation of the concept of virtual-real combination is analyzed. Secondly, the interaction methods of combining physical radar and virtual environment and virtual radar and physical environment are studied. Finally, combined with the specific training requirements, the application of real-real, real-virtual, virtual-real, and virtual-virtual radar interaction methods in radar training is analyzed in the same scenario.

The data fusion of radar and automatic dependent surveillance-broadcast(ADS-B) is the effective method to surveille the 'black flights' and flying birds. However, the tracking performance of the two sensors has large differences and is easy to be fluctuated, which will bring a decline in fusion accuracy. A data fusion method of radar and ADS-B based on track quality assessment is proposed. Firstly, the effects of local track accuracy, data update times and sensor measurement errors on local track quality on corresponding assessment factors are analyzed and quantified. And then, these assessment factors are combined to calculate the quality weighting factors of the local track, and the asynchronous track fusion processing of radar and ADS-B is completed based on the distributed fusion structure. Finally, the feasibility and effectiveness of the proposed method is verified with simulation experiment and application. The results show that the proposed fusion method can effectively improve the fusion accuracy, and the tracking errors are better than the traditional algorithms when the sensor tracking performance fluctuates.

Aiming at the current situation of lack of environment and equipment in radar training, a radar operation training method based on the combination of virtual and real is proposed. Firstly, the connotation of the concept of virtual-real combination is analyzed. Secondly, the interaction methods of combining physical radar and virtual environment and virtual radar and physical environment are studied. Finally, combined with the specific training requirements, the application of real-real, real-virtual, virtual-real, and virtual-virtual radar interaction methods in radar training is analyzed in the same scenario. [ABSTRACT FROM AUTHOR]

For calibrating the measurement error of the speed sensor and estimating the speed accurately while system is nonlinear and noise is non-Gaussian, dual radar and wheel axle sensor are configured and federal particle filter is used to acquire fusion. The whole operation process of CRH3 train from start to stop between two stations is taken as an example, the speed measurement errors of different speed estimation methods under the conditions of train idling, slipping, vibration and the speed sensor with dynamic noise are analyzed and verified. The simulation results show that: The root-mean-square error can be reduced by 31.52% and 47.35% respectively in the idling and sliding stages after the calibration of dual-radar and wheel-axle combination compared with no calibration; Compared with the two types of dual-radar calibration methods, the maximum relative error of the dual-radar separation vibration speed calibration method can be 39.66% lower than that of the dual-radar angle deviation estimation calibration method when the train vibration speed ratio is 0 to 1 and the radar installation angle error is -1° to 1°. Compared with the filtering results of dual radar and axle sensors before fusion, the speed measurement results after using joint particle filtering fusion are 34.71% and 14.03% lower in MAE, and 26.51% and 10.98% lower in RMSE respectively. Compared with federated extended Kalman filter fusion, the root mean square error of velocity measurement using federated particle filter fusion is 26.97% lower and the maximum absolute error can be reduced by 16.10%. [ABSTRACT FROM AUTHOR]

In the ground attack mission, the attack plan needs to be formulated and distributed to the attack aircraft based on the threat source intelligence data obtained in advance with the help of the tactical mission planning system. The passive radar reconnaissance and direction finding system can calculate the location information of threat sources and provide it to the task planning system by processing the received signal. When the enemy radar is a frequency diverse array system rather than a phased array system, the bending characteristics of the beam of the frequency diverse array radar can deceive the passive direction finding system. On the basis of analyzing the basic structure of frequency diverse array radar, this article compares the phase plane characteristics of phased array and frequency diverse array, and takes the interferometer direction finding system as an example to study the deception effect of frequency diverse array radar compared to phase method direction finding. The deception simulation results of several nonlinear FDA arrays show that the virtual transmitter intersection coordinate deviation of log-FDA is greater than that of sin-FDA. When the x-axis coordinate of the interferometer is xG=300 km, the virtual transmitter intersection coordinates gradually approach the actual position of the FDA array as the y-axis coordinate of the interferometer increases. The intersection offset is log-FDA>sin -FDA>reciprocal-FDA.

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In order to improve the operational effectiveness of multi-sensor cooperative detection of carrier-bome fighter, based on the scene of air interception, according to the combat airspace from far to near, the scene model of the extended range search of carrier-borne fighter, the radar infrared fusion detection, the cooperative guidance of formation and radar multi-beam detection are established. In the over-the-horizon, medium-range and short-range search phase, the extended range detection, interference and multi-beam detection in the multi-sensor cooperative detection mode are simulated and analyzed. According to the different combat distance, the design of multi-sensor cooperative detection mode under the combat flow is innovatively carried out. [ABSTRACT FROM AUTHOR]

With the acceleration of urbanization, the intelligent transportation has received more and more attention. Among them, the use of depth completion technology to extract the depth information of objects plays an important role in the realization of vehicle target tracking, distance calculation between targets and other tasks. However, multi-source depth completion data collected in practice often have correlation bias, resulting in knotty errors. In this regard, this study studies the depth completion technology based on multi-source data association fusion. The proposed technology enhances the depth map by calculating multi-channel confidence, and performs more accurate point-by-point correlation between the image and the millimeter-wave radar point cloud data. By designing a multi-scale attention fusion module, the adaptive fusion of multi-granularity associated data is realized to generate high-quality depth maps. In this study, a large number of experiments have been carried out in the public nuScenes data set. The experimental results show that the mean absolute error of our method is 1.142 m, which is lower than the 1.472 m of the existing benchmark method. [ABSTRACT FROM AUTHOR]

Most traditional multi-aircraft flight path optimization methods are oriented toward area coverage, use static optimization models, and face the challenge of model mismatch under complex dynamic environments. Therefore, this study proposes a flight path optimization method for dynamic area coverage based on multi-aircraft radars. First, we introduce an attenuation factor to this method to characterize the actual coverage effect of airborne radar on a dynamic environment, and we take the area coverage rate under the dynamic area coverage background as the optimization function. After integrating the constraints of multi-dimensional flight path control parameters to be optimized, we built a mathematical model for dynamic area coverage flight path optimization based on multi-aircraft radars. Then, the stochastic optimization method is used to solve the flight path optimization problem of dynamic area coverage. Finally, the simulation results show that the proposed flight path optimization method can significantly improve the dynamic coverage performance in dynamic areas compared with the search mode using preset flight paths based on multi-aircraft radars. Compared with the traditional flight path optimization method oriented to static environments, the dynamic coverage performance of our proposed method is improved by approximately 6% on average.

In order to study the waveform selection of radar seeker in the terminal guidance and tracking phase, this paper proposes a waveform selection algorithm in the guidance and tracking process of cognitive radar seeker. Firstly, we establish the processing flow of radar seeker waveform selection by combining the seeker guidance and observation filtering models; Secondly, we use the interactive multiple model unscented Kalman filter (IMMUKF) algorithm to solve the nonlinear tracking problem. We minimize tracking error by searching for waveform parameters based on the maximum mutual information criterion. The simulation results show that the waveform selection algorithm can effectively improve the seeker tracking accuracy and provide stable guidance overload. [ABSTRACT FROM AUTHOR]

Through flexible configuration of warship formation, the Aegis Warship Formation achieves interception and defense of targets in different attack directions. Based on the warship coordinate system and target coordinate system, the detection and interception zone models of Aegis warship formation are constructed. The functional simulation models of guidance radar and SM-3 interceptor are integrated to propose a dynamic simulation modeling method for anti-missile defense of warship formations. The detection directional coefficient and killing directional coefficient are defined, which are used to quantitatively evaluate the directional characteristics of the formation anti-missile defense. The simulations are conducted with a typical case of two-ship Aegis formation, and useful conclusions are obtained. The results can provide support for battlefield offensive and defensive situation assessment. [ABSTRACT FROM AUTHOR]

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To meet the needs of flight teaching and training, aiming at the interactive, multi-input multi-output and comprehensive sequential logic controlling characteristic of integrated avionics system display and control interface for fighters, a functional simulation method by designing display and control logic independently is introduced. On the basis of this structure, a loosely coupled, modular and visual simulation method of display and control interface for multi-function fire control radar is presented, and the realization of display and control logic based on Simulink/Stateflow is introduced. The application result shows that the program progress is more intuitive, and the code is more maintainable, so this design method can improve the fidelity and developing efficiency of display and control simulation. All these researches can provide technology reference for the simulation of display and control interfaces for avionics systems and its subsystems. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Harbin University of Science & Technology is the property of Journal of Harbin University of Science & Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

LFM-Chebyshev chaotic bi-phase code signal is a mixed signal which uses Chebyshev chaotic sequence as inter pulse two-phase coding and linear frequency modulation processing in the pulse. It has strong concealment and anti-jamming ability. In order to study the application value of LFM-Chebyshev chaotic bi-phase code signal in electronic countermeasures, based on the model and characteristics of LFM-Chebyshev chaotic bi-phase code signal, the jamming effects of five jamming styles, such as interval sampling and repeater jamming, convolution modulation jamming, frequency shift jamming, distance jamming and distance-frequency shift two-dimensional jamming, on LFM-Chebyshev chaotic bi-phasie code signal are simulated by MATLAB software. The characteristics and parameters set of the five jamming methods are analysed. Theoretical analysis and simulation results show that convolution modulation jamming is an ideal jamming mode for LFM-Chebyshev chaotic bi-phase code signal.

Radar uses electromagnetic waves to detect， track and locate objects at certain distances， which is widely used in military， meteorological， navigation and other fields. Radar emits electromagnetic waves outward and produces non-ionizing radiation， which may be considered as a physical occupational hazard. Epidemiological surveys found that long-term exposure to radar is associated with various adverse health effects， which may be correlated to transmitted power and frequency of radar， location of radar antenna， position of workers， and shielding effectiveness of cabins where work station is located. Based on radar frequency and electromagnetic radiation intensity， this study summarizes the health effects of radar on occupational population exposed to radar.

Aiming at the problem of aerosapce time-sensitive target recognition, a new sequential feature extraction method for radar high resolution range profile (HRRP) is proposed, and a multi classifier based on decision tree and support vector description (SVDD) method is designed. Firstly, the method estimates the radial size of the target based on time-series HRRP, uses sequential pulse accumulation to perform sliding window processing on the size estimation results, and obtains the four statistical characteristics of mean, range, median, and end mean of the radial size in each window. Then, The four types of features are spliced to obtain more robust high-dimensional features. Finally, the proposed multi classification SVDD method based on decision tree (Multi-SVDD-DT) is used to classify the obtained high-dimensional features. The simulation data experiments of four types of aircraft show that the proposed method can extract the robust features of the target, and can effectively complete the recognition task of aerospace time-sensitive targets.

In traditional radar object tracking algorithms, targets are regarded as points in tracking filtering algorithms. With higher resolution in range and azimuth directions, a target can occupy multiple resolution units, so radars can obtain high-resolution observation results. When point targets turn into extended objects, the traditional point target tracking filtering algorithms can hardly achieve stable tracking to the extended object due to the increasing complexity in data association. In this paper, a radar single extended object tracking algorithm is proposed based on correlation filtering algorithm in the computer vision field. This algorithm normalizes radar echoes to get the visual radar range-azimuth image firstly. Then, this image is transformed into the Cartesian coordinate system from the polar coordinate system. At last, the target appearance of the extended object are online learned by the correlation filter to realize the target tracking based on filtering response diagram. Real data based experimental results demonstrate that this algorithm can obtain the object location and size in each frame. Compared with traditional filtering algorithms, this algorithm is more accurate and robust.

Radar system environment is complex, and excessively high range sidelobes will cause weak targets to be lost and false targets. To solve this problem, a novel orthogonal frequency-division multiplexing(OFDM) radar low sidelobe waveform design method based on genetic algorithm(GA) is proposed. First, the OFDM waveform based on cyclic prefix(CP) is constructed. All sub carriers are modulated with m-sequence codes. Then, the main lobe and sidelobe ratio after pulse compression is taken as the objective function, and the phase parameter is taken as the optimization object. The objective function is transformed into an unconstrained optimization problem. Last, by using genetic algorithm to solve the optimization problem, the radar range sidelobe suppression is achieved. Theoretical analysis and simulation results show that this method can effectively suppress the range sidelobes.

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This paper presents a review of the scientific research progress of the lunar in-situ spectroscopy and radar, focusing on the important results obtained by the Chang'E-3 and Chang'E-4 missions. In terms of the spectral detection, we report the composition, the photometric characteristics, space weathering information and thermal radiation characteristics of the lunar surface. In terms of radar detection, the detection of geological subsurface structures of the Moon, the detection of possible cavities/lava-tubes, and the inversion of the dielectric properties of the lunar regolith are described. Finally, the future development trends of lunar in-situ spectroscopy and radar detection are discussed.

Copyright of China Mechanical Engineering is the property of Editorial Board of China Mechanical Engineering and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Aiming at the problem that it is difficult to directly test the intercepted distance between radar and specific ESM reconnaissance equipment, the equivalent test method of radar intercepted distance by ESM reconnaissance equipment is studied. Firstly, the equivalent model of intercepted distance under the expected test condition and the substitute test condition is deduced. Then, according to different test scenarios, the equivalent model is subdivided into four different types. Finally, the equivalent model is verified by the measured data. The data is from the intercepted distance of a certain radar in the outfield flight test. The test results show that the error of the equivalent model is 7.26%, which meets the requirement that the error of the test outline is less than 10%.

Distributed soft target refers to nonrigid target or a target group with wide distribution range, time-varying spatial distribution, or internal relative motion. This type of target is currently attracting considerable interest in the radar field, and the research on its radar characteristics and sensing technology is a typical interdisciplinary problem. To help the radar technicians better understand the related technologies, this study introduces the dynamics, scattering/transmission, radar characteristics, detection, and parameter retrieval of this type of target in continuous and discrete forms, as regards the positive and inverse problems. Considering the aircraft wake vortex as an example, the radar characteristics and sensing technology of this type of target are illustrated, which can serve as a good reference for the development of related radar detection technologies.

There is an urgent need for radar-measured data to tackle key technologies of radar maritime target detection. The ‘‘Sea-detecting X-band Radar and Data Acquisition Program’’, proposed in 2019, aims to obtain data through radar experiments and share them publicly. In 2020, the program continued to advance and conducted several experiments in three aspects, namely, Radar Cross-Section (RCS) calibration of radar targets, detection of sea clutter and target under different sea conditions, as well as detection and tracking of maneuvering targets in sea. The measurement data of the stainless steel sphere calibrator at different distances in radar slow-scanning mode, sea clutter in radar staring mode in different directions, sea target in radar staring mode, and marine engine speedboat in radar scanning mode are obtained. In addition, wind and wave data, data from the Automatic Identification System (AIS) of targets, visible/infrared data, and other associated sensor data are synchronously obtained.

To address the problems of the traditional regional road network path guidance system, such as the difficulty to effectively plan the optimal solution of the path and poor stability, the immune genetic algorithm was applied to the path guidance system. It connects the radar devices, infrared beacon identification and other devices with the path-induced control center to construct the hardware environment of the induction system. Then the immune genetic algorithm was used to expand the encoding of different initial points to determine the encoding path. Finally the optimal induction path was designed through the process of data evaluation, chromosome determination, path judgment and weight evaluation by combining the results of hierarchical search method and restricted region search method. The results show that the stability of the path guidance system using the proposed method is better, and the stability can reach 0.979. The intelligent path guidance system based on immune heredity can effectively determine the optimal solution of vehicle driving path, and can successfully achieve the optimal path guidance. [ABSTRACT FROM AUTHOR]

To meet the demand of large number and high integration of filters in the IF filter modules of radar receivers, a miniaturization LC filter based on the 3D integration technology is proposed in this study. The application and integrating process of 3D LC filter in modules are studied and analyzed. The 3D LC filter adopts two substrates, and uses 3D integration process and BGA technology to realize the three-dimensional integrated assembly of the two substrates. High-density layout can be realized by placing capacitive elements on the bottom substrate. Inductive elements are placed on the top substrate and separated from the capacitive elements, and signal communication is achieved through solder balls. The use of a three-dimensional integration scheme can reduce the size of the LC filter circuit by nearly 50%, and the filter index is consistent with the performance of the planar filter circuit. Compared with the traditional IF filter component design method, this solution is more conducive to achieve high integration and miniaturization. [ABSTRACT FROM AUTHOR]

Regarding the target characteristics in marine radar detection, this paper introduces classic radar target characteristics and models, and the main problems associated with the measurement and computation of these target characteristics. From three perspectives, i.e., the target, environment, and sensor, we discuss the target characteristic that have attracted much attention in the field of marine target detection. We discuss the diversity of marine target characteristics, the variety and complexity of the marine environment, coupling effects between the target and the environment, and the main requirements of the typical marine radar in target detection applications. The techniques used in the measurements and computation of target characteristic are also introduced. We propose a multidimensional representation of the target characteristics and briefly discuss its applications.

To meet the radar data requirements of target detection technology research and address the lack of publicly available sea-detecting radar data, a data-sharing program for sea-detecting radar is proposed herein. The aim of the proposed data-sharing program is to conduct sea detection experiments using an X-band solidstate phase-coherent radar and other multi-type radars to obtain the target and sea clutter data under different sea conditions, resolutions, and grazing angles. Moreover, the marine meteorological and hydrological data, target position, and track data are simultaneously obtained using the proposed data-sharing program to help achieve the standardized management of radar-measured data. The proposed data-sharing program aims to promote the open sharing of data sets, serve as the basis for research on sea clutter characteristics, and facilitate the research on sea clutter suppression and target detection technology.

In order to improve accuracy of vehicle forward collision prevention warning system on road environment perception, a vehicle tracking method of information fusion for millimeter-wave radar and vision sensor was proposed. An algorithm to eliminate radar jamming targets was proposed to reduce processing time of jamming targets. A symmetric detection algorithm was proposed to detect radar target ROI (region of interest) symmetrically and reduce lateral position errors of radar target ROI. In order to improve the tracking accuracy, a KCF-KF combined filtering algorithm was proposed to track and fuse vehicles. Actual vehicle tests show that the method may effectively track vehicle position information, and the tracking accuracy of X and Y coordinates in pixel coordinate system is more than 97.34% and 95.19% respectively. [ABSTRACT FROM AUTHOR]

In complex marine environments, sea clutter greatly affects the detection performance of maritime targets. Because the influencing factors of sea clutter are numerous and the mechanism is complex, there are great difficulties in feature description and sea clutter suppression, and it is necessary to carry out long-term, systematic, continuous, and in-depth research. Carrying out sea clutter measurement experiments and obtaining measurement data under the influence of different parameters is an important prerequisite for supporting this research. This paper mainly focuses on the sea clutter measurements that have been carried out. First, typical experiments in various countries such as Canada, South Africa, Australia, the United States, Spain, and Germany are categorized and summarized from the aspects of shore-based experiment and airborne experiment. Then, sea clutter measurement experiments with wave tank conducted by the United States and Japan are reviewed, and domestic sea clutter measurement experiments as well as the construction of the maritime target detection experimental center in Yantai are briefly introduced. Finally, the future research directions that should be emphasized are projected: more systematic and continuous sea clutter measurement experiments need to be conducted; experiment and data analysis under explicit task background need to be strengthened; and sea clutter and target datasets that meet the requirement of intelligent radar applications need to be urgently constructed.

Distributed Coherent Aperture Radar (DCAR) utilizes multiple separated antenna apertures to emit signals in the same space area, realizing spatial coherent synthesis of electro-magnetic waves. Such a flexible radar system has advantages such as higher resolution, greater radar power, and lower cost. Combined with microwave photonic technologies, which have merits in wideband signal generation, transmission and procession, the DCAR has a comprehensive and better performance. This paper introduces a microwave photonics-based high-resolution distributed coherent aperture radar that was proposed by researchers of Tsinghua University. Taking advantages of microwave photonic technology, a group of wideband orthogonal phase-coded linear frequency modulation waves is generated in the coherence-on-receive mode, with the frequency ranging from 8.5 GHz to 11.5 GHz, all with phase coding under a bit rate of 0.5 Gbps. The orthogonality of the signals is nearly 30 dB, and the range resolution is better than 0.05 m. While in the full coherence mode, the transmitted waveforms can be flexibly switched to the wideband coherent linear frequency modulation waves, and the full coherent synthesis can be realized. The waveforms generated by the proposed system can meet the waveform requirements of the DCAR in different operation modes. In the experiment, full coherence is achieved with two sets of radars, resulting a signal- to-noise ratio gain of 8.3 dB.

In view of real-time demand for speed compensation on high speed moving platform, an implementation method of missile speed compensation is proposed. After the idea of range cell migration compensation applied to the missile speed compensation, the signal-to-noise ratio of coherent accumulation is improved, and hardware design is realized on FPGA. The simulation experiment shows that the missile speed compensation method with FPGA has advantages of high real-time, fast processing speed and high precision.

This paper presents a radar working mode based on multi-pulse combination and coding, and the basic concept and theoretical model of pulse-coded radar are established. Using multi-pulse combination and the modulation of the time, frequency, and phase parameters, the pulse signal is coded in time domain, frequency domain, or time-frequency domain. Based on multi-pulse combination and coding, a new working method and theoretical basis are provided to solve the problem of coupling constraints among parameters of traditional pulse and continuous wave radars, which limits the performance of the radar system. Based on the fabricated Synthetic Aperture Radar (SAR) and its tests, the pulse coding, target signal recovery method, and pulse coding performance were studied. The study and test results show that the sampling rate of radar signals could be reduced to break through the limitation of Nyquist sampling theorem and simplify the difficulty of system implementation using frequency division pulse coding method. A 5 GHz bandwidth signal was sampled with 4.8 GHz and was recovered without distortion in the radar system, and an SAR imaging resolution of 0.03×0.03 m was realized. By using the time domain pulse coding method with an increase of duty cycle, the signal-to-noise ratio was improved by over 20 dB. By using the two-dimensional pulse coding method, the SAR signal ambiguity was removed, and the imaging swath of over 90 km was realized. The theoretical and test results verify the significant advantages of the pulse coding method in improving radar performance, by which a new technical approach for the realization of high performance radar system is provided.

Electromagnetic waves are transmitted by radars and reflected by different objects, and radar signal processing is highly significant as its analyses can lead to the acquisition of important information such as the situation and radial movement speed. Moreover, deep learning has gained much attention in several fields, and it can be utilized to implement radar signal processing. Compared with the traditional methods, deep learning can realize automatic feature extraction and yield highly accurate results; hence, in this paper, the application of deep learning algorithm in radar signal processing is studied. In addition, the study directions in radar signal processing are summarized into overfitting and interpretation. Thus, these two issues are being considered.

In this paper, we review the recent developments on information metamaterials, including digital metamaterials, coding metamaterials, and programmable metamaterials; furthermore, we discuss their applications in the terahertz (THz)-frequency region. In addition their flexibility to manipulate the electromagnetic waves, the physical principle, numerical simulation, fabrication, and application of information metamaterial are discussed in detail. Moreover, we developed and applied a coding metasurface that works in the THz band. Furthermore, the principle of real-time programmable metamaterials and their application in novel imaging systems and radar systems are illustrated. Information metamaterials and metasurfaces can be used for various functional devices such as beam splitting and low radar cross section, which open up a novel route to manipulate THz radiations.

Copyright of China Mechanical Engineering is the property of Editorial Board of China Mechanical Engineering and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Aircraft wake vortex is a pair of strong counter-rotating vortices and has attracted considerable attention in various fields including aviation safety and atmospheric physics. The characteristics and detection of wake vortex act as the basis for both behavior prediction as well as hazard assessment. This paper provides a short survey of the characteristics and detection researches. Initially, the wake vortex is classified as clear-air wake vortex (i.e., wake turbulence and contrail) and precipitation wake vortex (i.e., under rainy, foggy or snowy condition). Subsequently, the dynamics and scattering are introduced, and the main verdicts are: the radar (radio detection and ranging) scattering of wake vortex is relatively weak under clear air conditions, but the Lidar (Light detection and ranging) scattering is appreciable owing to the presence of particles such as aerosols. Wake vortices under precipitation conditions and contrails possess relatively good radar reflectivity owing the strong scattering characteristics of precipitation droplets and ice crystals. Furthermore, we have introduced a joint detection scheme of Lidar and radar for wake vortex along with parameter-retrieval algorithms. Finally, we have presented our conclusions and intended future research.

To obtain an accurate polarization scattering matrix, simultaneous full polarization radar systems must transmit two signals. The performance of orthogonal polyphase codes designed by the traditional method is limited by the code length and is sensitive to Doppler frequency. In this paper, we propose a design method for orthogonal polyphase codes that have good Doppler tolerance. We consider the peak sidelobe level and isolation and transform the signal design problem into a nonlinear optimization problem, which we solve using a genetic algorithm. Our simulation results show that our proposed orthogonal polyphase codes have better Doppler tolerance and their peak sidelobe levels and orthogonal performances are 1.5～2 dB better than the codes designed by Deng or Khan. As such, the new design can improve the measurement accuracy of simultaneous full polarization radar systems.

In this study, a new type of Continuous Wave (CW) signal modulated by pseudocode family is designed, solving the problem of more quantity of warhead dynamic fragments, larger speed variation, larger distribution and more difficult resolution during the measurement of warhead dynamic fragments. This signal has thumbtack ambiguity function and multiresolution characteristics. It can meet the measurement needs very well. Herein, correlation properties and ambiguity function characteristics of this signal are analyzed. Moreover, the signal’s limitations are reported. Recommendations pertaining to signal selection, number option, and usage are presented. The analysis results show that this signal can be used for dynamic fragments measurement of warhead. This signal is also of great importance to improve complex waveform design and radar performance.

This study uses time domain terahertz radar system to discuss systematic imaging studies on the scaled models based on the improved Back-Projection (BP) algorithm. We image the scaled models with different shapes and are able to distinguish spatial gaps as small as 6 mm. The Theoretical calculation predicts that the lateral resolution and the axial resolution can be as high as 0.125 mm. Center enhancement and background rings caused by the algorithm in the imaging results are also qualitatively analyzed and are proposed methods to overcome this problem.

In view of shortcomings of bad anti-interference and low reliability existed in ultrasonic measurement method for coal level measurement, a mine-used radar material level monitoring device was designed. The device transmits high frequency electromagnetic wave to the measured object by material level sensor and processes reflected signal by use of noise threshold processing technology, filtering processing technology and false echo processing technology, so as to realize real-time and accurate measurement of material level. The testing results show that the device has high reliability, small measurement error and strong anti-interference.