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In this paper, we present the results of a special experimental study of quiet-time behavior of the mid-latitude ionosphere over Eastern Europe by synchronously operation of different ground-based facilities. For the first time we used data obtained from Kharkiv incoherent scatter (IS) radar, ionosonde and coherent Doppler HF sounding system to detect and investigate traveling ionospheric disturbances (TIDs). The periods close to winter solstice and autumn equinox in 2018 were analyzed. The dominant periods and horizontal phase velocities of registered TIDs were 45–80 min and 230–460 m s−1, respectively. The strongest signatures were observed in the solstice measurement and represented by large amplitudes. Based on results obtained by all three methods, we found the LS TIDs with the same interval of time and altitude of propagation and similar characteristics (the period of about 50 min, estimated vertical 80 m/s and horizontal 460 m/s velocity and horizontal spatial scale size about 1360 km) for winter measurement. Such observational findings confirm the reliability of these TID detection techniques. Possible sources of TIDs generation were considered including solar terminator. [ABSTRACT FROM AUTHOR]

• Middle atmosphere dynamics and coupling using three decades of Indian MST radar and complimentary observations. • Highlighted recent results on waves, tides, planetary waves, tropopause, STE processes and low-latitude mesospheric dynamics. • Gap areas and scope for future study using other complementary techniques are mentioned. The genesis for Indian Mesosphere-Stratosphere-Troposphere (MST) radar came from the Indian Middle Atmospheric Programme (IMAP) to study the middle atmospheric dynamics and its underlying processes. During the early 1990s VHF radar operating at 53 MHz has been set up at Gadanki (13.5°N, 79.2°E), India, which started operating initially in the stratospheric and tropospheric (ST) mode. It is upgraded to MST mode in 1993. Since then, it has served various scientific experiments not only from India but under international collaboration. Numerous focused campaigns that have national and international importance were conducted. Using this unique data in the last 30 years along with complementary measurements, several stimulating results has been reported covering a wide range of topics that includes gravity wave characteristics, tides, planetary waves, oscillations, tropopause dynamics and stratosphere-troposphere exchange processes, monsoon dynamics and circulations, mesospheric structure and dynamics, vertical and lateral coupling and long-term trends. The present communication will highlight the unique results obtained using long-term observations of Indian MST radar and complementary techniques covering the complete middle atmosphere. Unique results include quantification of the momentum carried by the high-frequency waves generated in the troposphere up to the mesosphere, demarcating the complete tropical tropopause layer using MST radar observations alone, indication for the strengthening of the tropical easterly jet in the recent decade, unusual behavior of the Hadley circulation during drought and El Nino years, the revelation of the mechanisms for the occurrence of mesospheric echoes at the tropical latitudes, quantification of the turbulence, evidence for the role of anthropogenic changes on the dynamics of the mesosphere and generation of the empirical model by combing multi-instrument data sets. These data set also served in validating numerous ground-based and space-borne measurements including several re-analysis products over a tropical latitude. Issues remained unresolved and ways to tackle in future experiments are highlighted. [ABSTRACT FROM AUTHOR]

This study focuses on the improvement of the tracking performance of space observation radar systems. Coherent radar systems usually provide an observation vector including four observables (range, range rate, azimuth, elevation) measured at a given epoch. Moreover, for some coherent radars, such as the TIRA system, it is possible to determine an additional parameter, the range rate, which is extracted from the collected complex amplitude. The tracking performance can be improved by increasing the observation parameter accuracy. The influence of each parameter on the overall tracking performance can be assessed by conducting a sensitivity analysis. The investigation shows that the best way to increase the accuracy of the state vector is by improving the angle estimates. The TIRA system is equipped with a tracking radar and an imaging radar. A powerful solution to improve the tracking performance is the realization of a multi-sensor data fusion between the two radars of the system. [ABSTRACT FROM AUTHOR]

This review article provides an overview of various aspects of lunar exploration, including missions to the Moon, collection and analysis of lunar sample data in laboratories, and the processing and analysis of remote sensing data, particularly using radar techniques. Both remote sensing and in-situ methods are critical for advancing our understanding of the lunar surface and its properties. This review article focuses on the identification and quantification of water–ice deposits located in areas such as Permanently shadowed areas (PSRs) and the lunar poles (section " Lunar Poles and PSRs: A Special Environment "). These volatile resources have the potential to serve as valuable sources of fuel for future missions, making it crucial for the lunar community to determine their abundance and distribution. After thoroughly examining lunar samples using high-precision laboratory techniques, many preconceptions were dispelled which is highlighted in the section " Laboratory Investigation of Lunar samples ". But as in-situ observations are difficult to acquire, especially terrestrial bodies samples, remote sensing techniques allow the global understanding of the surface. The article specifically highlights the importance of understanding the electrical characteristics of the lunar surface and how radar inversion can provide valuable information in this regard. The " Conclusion " section of this review article serves as a key takeaway for readers, underscoring the critical role that both in-situ and remote sensing techniques play in advancing our understanding of the Moon. [ABSTRACT FROM AUTHOR]

• A frequency-domain retracker with interface to In-Flight Point-Target-Response. • Assessment of the impact of In-Flight Point-Target-Response for Sentinel-6 MF. • The range walk correction applied via a Chirp-Zeta-Transform algorithm. • Assessment of the impact of the range-walk correction for Sentinel-6 MF. • A full Cal/Val of the first year of Sentinel-6 MF altimetry science data. Poseidon-4 is a dual-frequency redundant radar altimeter on board the European Commission Copernicus Programme Sentinel-6 Michael Freilich satellite, that represents a significant breakthrough with respect to its predecessors Jason-class altimeters due to its digital architecture and to its innovative measurements and calibration modes. In the framework of the Sentinel-6 Michael Freilich commissioning preparatory activities, CNES has contracted CLS for the development of a Sentinel-6 Processing Prototype (S6PP) application. S6PP is a multi-chain processing suite able to process Sentinel-6 Level-1A and Level-1B data products up to Level-2. The novel algorithms developed in the CNES/CLS research and development activities are implemented within S6PP and validated to support the different thematic applications (in particular inland water and ocean) and in view of promoting them for possible implementation in the operational ground segment. The present work covers in particular the main results over open ocean for the main altimetric geophysical variables over the sea surface (sea surface height anomaly, significant wave-height, sigma-nought and wind speed) derived by the Low-Resolution Mode (LRM) and High-Resolution Mode (HRM) chains of S6PP in terms of precision, accuracy, spectral content and measurement stability. Given the reported variation of the payload in-orbit temperatures along with the reported instrumental ageing, and given the tight requirement to measure the GMSL (Global Mean Sea Level) in seamless continuity with Jason-3, the clear goal for S6PP was to process the S6-MF data with the minimum possible level of approximations along the processing pipeline but still maintaining a very efficient prototype from the computational point of view. For this scope, a novel and computationally efficient numerical retracking scheme with interface to the in-flight PTR (Point Target Response) provided by the instrument calibration chain has been put in place within S6PP for both the Low-Resolution and High-Resolution modes whereas the Delay-Doppler beam-forming is carried out by applying the range walk correction based on a computationally efficient algorithm (Chirp Zeta-Transform). The impact of the range walk correction and of the in-flight PTR interface is assessed for HRM and LRM, respectively. The paper shows that the proposed processing baseline ensures a dataset robust from the currently known instrumental degradation or ageing issues, both in LRM and HRM mode and, once this is done, that Sentinel-6 Michael Freilich global mean sea level measurement is in line with the one measured by Jason-3. [ABSTRACT FROM AUTHOR]

Calibrating the relative positional posture of the roadside sensor with respect to the road is crucial for target tracking and sensor fusion. However, most previous studies rely on prior information or require additional manual measurements, which increases calibration error and labor costs. This paper proposes an automatic extrinsic parameters calibration method for roadside integrated radar camera fusion sensors for the first time. In particular, we leverage the radar camera fusion framework to automatically reconstruct the road plane. Specifically, to integrate sensing abilities, a stable bidirectional selection association method is adopted to match radar and camera trajectories. Based on the association results, the Extended Kalman Filter (EKF) is adopted to fuse pixel positions and three-dimensional (3D) velocities of vehicles, and then a series of 3D positions of vehicle bottoms are obtained to reconstruct the road plane. Experimental results show that our proposed method achieves automatic and accurate calibration of extrinsic parameters. • An automatic extrinsic parameters calibration method. • Calibration method for roadside radar camera fusion sensors for the first time. • Use radar to provide scale factors, thus eliminating the need for prior information. • The method is tested in real-world scenarios and achieves promising performance. • Experiments verify that the proposed method is robust to data association results. [ABSTRACT FROM AUTHOR]

During deorbiting, be it natural orbital decay or otherwise (e.g. self-disposal or active debris removal), precise knowledge of the condition of the target is of critical importance. The Tracking and Imaging Radar (TIRA) is an instrument that possesses the ability to accurately determine satellite and space debris orbits while also generating detailed radar images of them. We present recent results from the characterization of deorbiting satellites and space debris employing TIRA. Drawing examples from orbital decay events (Tiangong-1, Soyuz 2.1v R/B), deorbiting (Tiangong-2) and self-disposal operations (Carbonite-1, MicroSCOPE), we demonstrate the potential of TIRA. Furthermore, we focus on the emerging field of active debris removal (ADR), where reliable information of the on-orbit status and attitude motion of potential targets can "make or break" an ADR mission. In this context, the on-orbit status of a JAXA R/B (43682) and a VESPA adapter (39162) are investigated. We employ inverse synthetic aperture radar (ISAR) imaging and 3D modelling of ISAR images, obtained with TIRA, to characterize the status and attitude motion of satellites and space debris. When certain conditions render direct imaging unsuitable, the more powerful L-band tracking radar of TIRA is used to obtain and analyze the temporal evolution of their radar cross-section (RCS). In this work, we employ for the first time, a wavelet time–frequency analysis of such RCS signatures, specifically of NABEO-1 (43692) in LEO and an Ariane 5 rocket body (28904) in geostationary transfer orbit (GTO), to characterize their on-orbit status. The wavelet analysis delivers results in good agreement with more traditional tools, with added information on time localization of periodicities. We are thus able to confirm the tumbling motion of NABEO-1 and constrain the rotational velocity of Ariane 5 upper stage (28904). [ABSTRACT FROM AUTHOR]

This work outlines and assesses several methods for the detection of manoeuvres in Low Earth Orbit (LEO) from surveillance radar data. To be able to detect manoeuvres, the main starting assumption is that the object under analysis has an orbit known with a sufficient degree of precision. Based on the precise (a posteriori) orbit and radar data, several manoeuvre detection methods are presented; one is based on unscented Kalman filtering, whereas two others algorithms are based on reachability analysis of the state, which correlates its prediction set with the next track from the radar. The filtering algorithm can be extended for several radar tracks, whereas the reachability-based methods are more precise in detecting manoeuvres. Then, to inherit the best properties of both classes of algorithms, a manoeuvre detection filter that combines both concepts is finally presented. Manoeuvre detection results are analysed first for simulated scenarios—for validation and calibration purposes—and later for real data. Radar information comes from the Spanish Space Surveillance Radar (S3TSR), with real manoeuvre information and high-quality ephemerides. The results show promise, taking into account that a single surveillance radar is the only source of data, obtaining manoeuvre detection rates of more than 50% and false positive rates of less than 10%. [ABSTRACT FROM AUTHOR]

Curved periacetabular osteotomy (CPO) is indicated for patients with developmental dysplasia of hip (DDH) to prevent progressive osteoarthritis. Patients with DDH have not only lateral acetabulum dysplasia but also anterior and posterior dysplasia. The full circumference acetabular coverage angle (ACA) of the femoral head should be evaluated preoperatively. This study aimed to determine the full circumference ACA in the patients with DDH before and after CPO compared with the coverage in normal patients. Twenty-three patients (a total of 24 hips) with DDH undergoing CPO between February 2006 and March 2014 were included in this study. The normal group was defined as the normal side in patients with unilateral osteonecrosis of the femoral head (ONFH) and the non-collapsed femoral head side in patients with bilateral ONFH. Pre- and postoperative hip functions were evaluated using the Japanese Orthopedic Association (JOA) hip score. ACA was measured using pre- and postoperative three-dimensional computed tomography (3DCT) and described as a clock using a radar chart. The ACA of the normal group was evaluated in the same manner as that for patients who underwent CPO. The ACA before CPO was compared with the ACA after CPO, the ACA before CPO was compared with that of the normal group and the ACA after CPO was compared with that of the normal group at each location. The mean JOA hip scores improved significantly from 69 preoperatively to 88 postoperatively. The superior, posterior, and anterior ACA after CPO significantly increased and the inferior ACA decreased compared with ACA before CPO. The superior, posterior, and anterior ACA before CPO were significantly smaller than ACA in the normal group. The ACA after CPO were similar to the normal group. CPO improved the anterosuperior coverage of the femoral head but reduced its inferior coverage. The radar chart could visualize acetabulum full circumference and was useful for three-dimensional pre-postoperative evaluation. [ABSTRACT FROM AUTHOR]

• Evolving the Radar System Simulator into the Sensor Network Simulator. • Newly implemented Optical Performance Model was verified and validated with real data. • The SNS tool suite can be used to analyze sensor networks and their performance. The number of human-made objects orbiting the Earth is growing steadily. This trend is further accelerating during recent years due to increasing commercialization in the field of satellite operations and an increasing launch rate. Concerning the area of space surveillance and tracking (SST), this leads to higher demands with respect to object observation capabilities. In order to ensure the safe usability of the different Earth orbits for all spacecraft operators, it is of great importance to continuously observe and catalog as many of the human-made objects as possible. This is especially true for inactive and uncontrollable objects, i.e. space debris. Only by maintaining accurate catalogs of the space debris environment, involuntary collisions can be avoided and risks of losing a spacecraft kept low. While the number of space debris objects can only be expected to further increase, it is not trivial to increase the number of observation sites, such as telescopes and radars, or their capabilities to counter this. One way to increase the observation capabilities without constructing new observation sites is to search for possibilities to improve the efficiency with which the existing sensors observe objects. With the goal to study and analyze single sensors, sensor networks, and how they can be used in the most efficient way, a sensor network simulator tool suite has been developed at the Institute of Space Systems of the Technical University of Braunschweig. Originally, the tool suite was developed as a radar system simulator concentrating on the different radar system configurations, such as reflector antennas or phased arrays that are used in a mono- or bistatic mode. Additionally, the corresponding radar performance model is able to simulate a tracking as well as a scanning mode. Building upon this tool suite, it is now extended to include an optical performance model and the possibility to simulate not only ground-based but also space-based sensors. Within this work, the preliminary results obtained with the newly implemented optical performance model are shown. Using the enhanced version of this sensor network simulator tool suite, thorough analyses can now be made using the radar and optical performance models. Sensor networks consisting of radars and telescopes being both ground- or space-based can be studied in different configurations. Thereby, different aspects, such as observation strategies, sensor tasking, or choosing the right location and sensor to reach a certain goal can be investigated. [ABSTRACT FROM AUTHOR]

Ground-based radar systems are critical for physical and dynamical characterization of near-Earth objects (NEOs) and space debris. The operational aspect and applications of radar for planetary defense and space situational/domain awareness (SSA/SDA) are similar, but there are some factors that should be taken into account for an instrument to support both areas: planetary defense is focused on asteroids and comets in heliocentric orbit with perihelion distance <1.3 au. Special attention is given to potentially hazardous objects (PHOs), which are NEOs larger than 140 m that can come within 0.05 au (∼20 lunar distances) of Earth. Radar can quickly and accurately determine NEOs' future trajectory, therefore, the sooner an object can be observed, the safer it is to assess any possible threat. Radar is also useful to help obtaining information about the objects' properties to plan for an impact mitigation mission if needed. For SSA, the focus is artificial objects orbiting Earth. This document presents the radar capabilities of the legacy Arecibo telescope, and explores synergistic future concepts for planetary defense and SSA. • The Arecibo Observatory had the most powerful planetary radar system in the world. • Arecibo supported planetary defense that focuses on near-Earth asteroids and comets. • Ground-based radars are critical for characterization of near-Earth objects. • Space Situational Awareness uses ground-based radar for space debris studies. • Synergistic use of radar system for planetary defense and debris should be explored. [ABSTRACT FROM AUTHOR]

It has been shown that bistatic radars using radio telescopes as receivers can be used to increase the sensitivity of orbital debris measurements over traditional terrestrial monostatic radar. A method to calculate the lateral surface area of a bistatic radar is needed to evaluate the efficacy of a proposed bistatic radar configuration for orbital debris measurements. For over three decades, models of the orbital debris (OD) environment in low Earth orbit (LEO) have been developed to assess the risk posed by OD to spacecraft. While terrestrial radar measures debris 3 mm and larger and in situ measurements provide data for debris smaller than 1 mm, no good data sources exist for debris between 1 mm and 3 mm in size. This results in large variations between competing OD models. It also happens to be the size regime which poses the highest mission-ending risk to spacecraft. It is, therefore, of interest to investigate potential new data sources for this under-sampled size regime. There are many radars and radio telescopes that could be combined to create sensitive bistatic radars that could potentially bridge the size gap. In addition to sensitivity, it is necessary to predict the expected count rate of a candidate sensor to evaluate its performance. NASA's Orbital Debris Engineering Model (ORDEM) can be used to predict the flux of debris passing through the line of sight of a radar or telescope. This flux is related to a count rate through the calculation of the lateral surface area of the sensor. While this can be done easily for monostatic radars, a method for calculating the lateral surface area of a bistatic radar is needed. This new method of calculation has been developed and is described. The new method maps the radar beam overlap in 3D space, calculating the area of the complex surface formed by the gain product of the two antennas. Comparisons of the monostatic and new bistatic lateral surface area calculation methods for the monostatic case are presented. Results of a sample lateral surface area calculation for a bistatic radar observation configuration currently employed by NASA are shown. Finally, a guide for total error as a function of baseline and target altitude is established. [ABSTRACT FROM AUTHOR]

The construction of the distribution of the flux density of meteor bodies over the celestial sphere is necessary for solving problems of meteor astronomy and others. To construct such distributions, experimental data on the coordinates of meteor radiants are needed. Meteor radars provide determination of the coordinates of the radiant in the presence of one transmitter and three spaced receivers. In this research, we are talking about ground-based meteor observations of the number of meteors using single-station meteor back-skatter radars as simpler than measurements of meteor radiants. In the 1950–80s in Kharkiv (Ukraine), active meteor radar research was carried out, both simple single-station and complex with remote points. The authors in the 1980s were participants in the meteor international program GLOBMET (Kashcheev, 1982; Roper, 1990). At that time, they modified an algorithm for calculating the flux density of meteor bodies over the heliocentric celestial sphere by number, range and velocity for radar observations with using single-station meteor backscatter. An algorithm was developed for dividing the celestial sphere into regions with a combination of "celestial" and "antenna" regions with a binding of a meteor to the antenna region in radar observations with a narrowly directed antenna without goniometr. This algorithm was applied to specific equipment for measuring the number of meteors by the Kharkiv Meteor Automated Radar System (MARS), 31.1 MHz. The correctness of the algorithm was confirmed by constructing the density distribution of the incident flux over the celestial sphere based on measurements in October-December 1989. The distributions are constructed using two methods for approximating the amplitude-time characteristics of signals. The results represent the experience of past years, which may be of interest as a scientific and technical solution. [ABSTRACT FROM AUTHOR]

This paper is concerned with the measurement outlier-resistant mobile robot localization problem by using multiple Doppler-azimuth radars under round-robin protocol (R-RP). In the considered robot localization system, multiple Doppler-azimuth radars are equipped on the robot platform to produce the measurement including the Doppler frequency shift and the azimuth. In order to assuage communication link congestion, the R-RP is used. For mitigating the influence of outliers, a time-varying state estimator is constructed which contains a saturation function with variable saturation levels. This paper aims at seeking out a practicable yet effective solution to the addressed robot localization problem by devising the constructed estimator which can assure that, over a finite horizon, the localization error satisfies the given H ∞ performance index. By constructing an appropriate Lyapunov function, the sufficient condition, which can guarantee the localization error to fulfill the given H ∞ performance, is established. Then, by resorting to the solution to a set of linear matrix inequalities, the constructed estimator can be devised. In the light of the estimator design strategy proposed in this paper, the corresponding robot localization algorithm is developed. At last, some simulations are conducted to testify the usefulness of the developed robot localization algorithm. • The measurement outlier and the round-robin protocol are considered simultaneously for the robot localization problem for the first time. • A discrete state estimator containing a saturation function with the variable saturation level is constructed. • By using Lyapunov theory and the RLMI method, the estimator is designed. • The corresponding measurement outlier-resistant robot localization algorithm is given. [ABSTRACT FROM AUTHOR]

In this study, a short-range mmWave radar is proposed for obtaining non-contact, non-invasive, and high-accuracy measurements of multiple vital signs. The system can extract the heart rate (HR), respiration rate (RR), and blood pressure (BP). A compact radar sensing unit operating at 122 GHz was used to transmit and receive signals reflected off a patient's chest under breathing and non-breathing (breath-holding) conditions. Algorithms were developed for extracting the BP values. The BP values were determined as 129/80 and 129/83 for the breathing and non-breathing signals, respectively. Furthermore, the extracted data were used to calculate the HR and RR based on the period of each data cycle and a fast Fourier transform (FFT). Both techniques yielded an RR of 12 breaths per minute. The HR values for breathing and non-breathing were 68 and 53 beats per minute, respectively. Furthermore, the HRs computed from the FFT of the breathing and non-breathing signals were 55 and 53 beats per minute, respectively. All values were consistent with the reference values. Thus, the system shows feasibility for low-cost, highly accurate, and continuous patient monitoring. [ABSTRACT FROM AUTHOR]

Given the recent surge in severe weather phenomena, the development of reliable computational resources that could assist meteorologists in issuing weather alerts is of great importance. To this end, deep learning models are being intensely studied for developing short-term weather forecasting tools using radar data. A drawback of these approaches, however, is the fact that their predictions tend to be blurry. In this paper, we aim to improve the visual quality of the predicted radar maps by introducing a new approach for designing perceptual losses which uses autoencoders as feature extractors. Compared to perceptual losses using VGG networks, our proposed approach uses fewer computational resources and no additional annotations or data sets. Experiments on radar reflectivity data collected by MET Norway show that the proposed method is able to provide visually sharper predictions than related work loss functions, while achieving an improvement of up to 6.45% in terms of root-mean-square error and of up to 17.65% in terms of false alarm ratio. [ABSTRACT FROM AUTHOR]

This paper proposes a new dual-band difference (DBD) method to retrieve total electron content (TEC) in Martian ionosphere with the dual-band echoes of the Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS). It establishes the relationship between the group delay difference of two-band echoes and the plasmas frequency. Then the Martian ionospheric parameters are solved with this equation. Then the TEC is calculated by integrating the vertical distribution model of Mars electron density. This method is used to calculate the TEC of the typical ionosphere in the southern hemisphere of Mars, and the comparison with previous results validates this method. The experiments prove that this method can not only calculate the TEC of dayside and nightside in different periods, but also effectively eliminate the influence of ionospheric dispersion on radar echoes. Moreover, the time variation characteristics of the ionosphere are analyzed. According to the characteristics of this algorithm, the error sources are analyzed. By calculating the influence of different parameters on the results, it is proved that the maximum error of the algorithm is less than 0.1 TECU. [ABSTRACT FROM AUTHOR]

• Ratios of E-CHAIM model-to-RISR radar measured electron density are close to one at heights near F2 peak. • On average, E-CHAIM underestimates electron density at ionospheric topside and bottomside by ∼ 20 % • E-CHAIM underestimations are strongest in summer and equinoctial nighttime at bottomside and in autumn nighttime at topside. In this study, predictions of the E-CHAIM ionospheric model are compared with measurements by the incoherent scatter radars RISR at Resolute Bay, Canada, in the northern polar cap. Reasonable coverage was available for all seasons except winter for which no conclusions were drawn. It is shown that ratios of the model-to measured electron densities are close to unity in the central part of the F layer, around its peak. This is particularly evident for summer daytime. Distributions of the ratios are wider for other seasons indicating larger number of cases when the model underestimates or overestimates. E-CHAIM underestimates the electron density at ionospheric topside and bottomside by ∼ 10–20 %. At the bottomside, the underestimations are strongest in summer and equinoctial nighttime. At the topside, the underestimations are strongest in autumn nighttime. Model overestimations are noticeable in the middle part of the F layer during dawn hours in autumn. Overall, the model tends to not predict highest-observed peak electron densities and the largest-observed heights of the peak. [ABSTRACT FROM AUTHOR]

This paper presents an approach to ensuring the safety of a landing module on a threat during its splashdown in the World Ocean. We propose mathematical methods and software to predict the main hydrophysical disturbances from underwater vehicles, which are necessary to estimate artificial anomalies on the sea surface. • Detection of underwater objects ensures safety of the spacecraft splashdown. • Underwater object creates identifiable hydrophysical anomalies. • Computer technologies can predict hydrophysical anomalies. • Analysis of radar images of anomalies allows to detect an underwater object. [ABSTRACT FROM AUTHOR]

Penetration path planning for stealth unmanned aerial vehicles (SUAVs) in the integrated air defense system (IADS) has been a hot research topic in recent years. The present study examines penetration path planning in different threat environments. Firstly, for the complex terrain and static radar threats, a modified A-Star algorithm containing the bidirectional sector expansion and variable step search strategy is proposed to elude static threats rapidly. Then, with regard to bandit threats, the minimal radar cross-section (RCS) tactics are presented to achieve path replanning. Furthermore, the combinatorial methodology of the minimum RCS tactics and the modified A-Star algorithm is applied to achieve the dynamic path planning for SUAV. The simulation results indicate that the modified A-Star algorithm and minimal RCS tactics can significantly reduce the probability of radar system, which has better superiority in calculation efficiency, path cost and safety. And the minimal RCS tactics have better real-time performance and are more convenient in dealing with dynamic threats, which enhances the survivability of SUAV and verifies the effectiveness of the proposed methodology. • This paper presents a novel framework to settle dynamic path planning problem for stealth unmanned aerial vehicles. • A modified A-Star algorithm that adopts the bidirectional sector variable step search strategy. • The minimal radar cross-section tactics are convenient to deal with the bandit threats and enhance real-time performance. • The combinatorial methodology has better superiority in calculation efficiency, path cost and safety. [ABSTRACT FROM AUTHOR]

• Finds all efficient routes of an UAV considering distance and threat objectives. • The UAV can move to any point in the continuous space. • Characterizes efficient trajectories between target pairs by a fitted curve. • Outperforms discretized case in solution quality and computational effort. We consider the route planning problem of an unmanned air vehicle (UAV) in a continuous space that is monitored by radars. The UAV visits multiple targets and returns to the base. The routes are constructed considering the total distance traveled and the total radar detection threat objectives. The UAV is capable of moving to any point in the terrain. This leads to infinitely many efficient trajectories between target pairs and infinitely many efficient routes to visit all targets. We use a two stage approach in solving the complex problem of finding all efficient routes. In the first stage, we structure the nondominated frontiers of the efficient trajectories between all target pairs. For this, we first identify properties shared by efficient trajectories between target pairs that are protected by a radar. This helps to structure the nondominated frontier between any target pair by identifying at most four specific efficient trajectories. We develop a search-based algorithm that finds these efficient trajectories effectively. For the second stage, we develop a mixed integer nonlinear program that exploits the structured nondominated frontiers between target pairs to construct the efficient routes. We compare the nondominated front we generate in the continuous space with its counterpart in a terrain discretized with three different grid fidelities. The continuous space representation outperforms all discrete representations in terms of solution quality and computational times. [ABSTRACT FROM AUTHOR]

• A review of track detection algorithms across different research fields. • Technical description of the initiation, maintenance and termination of a radar track in the BIRALES radar. • Presentation of a new track detection strategy that is used for the detection of orbital debris using a bi-static continuous-wave radar. • Performance evaluation of this new track detection method on synthetic data. The world's economy has become heavily dependent on the services provided by satellites. With the exponential increase in satellite launches, the population of defunct or inactive hardware in space has grown substantially. This is especially true in sensitive orbits such as the Low Earth Orbit (LEO) and Geostationary Earth Orbit (GEO) regimes. These objects, collectively known as orbital debris, can reach speeds of up to 28 000km h−1 in LEO. At these orbital speeds, even the smallest of objects can pose a considerable threat to operational satellites or astronauts. This makes the monitoring, and detection, of these objects of the utmost importance. This work describes the latest detection strategy used in one of Europe's largest Space Situational Awareness (SSA) installation; the BIstatic RAdar for LEo Survey (BIRALES) space debris radar. We present a novel bottom-up approach that makes use of single-linkage clustering to identify faint radar streaks in spectrogram data. Tests on synthetic data have shown that the detection strategy presented in this study obtains a higher detection rate when it is compared against existing methods. Unlike other approaches, this detection strategy, using the Multi-beam streak detection strategy (MSDS) algorithm, was still able to recall 90% of the track information at an Signal-to-Noise Ratio (SNR) of 2dB. [ABSTRACT FROM AUTHOR]

Millimeter wave applications gives an efficient solution to furnish peak data rates in indoor wireless access systems. Propagation of the signal will get up-shot because of few considerations in advanced communication appliances. Superior output and high directivity antennas are mandatory to overcome these consequences. By installing unequal slots in the structure, the tree-shaped unequal slotted antenna is analyzed for the variations in impedance, directivity changes and reflection coefficient. The better quality results have been observed for the proposed structure while compare with existing structures. The maximum simulation reflection coefficient(S11) of tree-shaped unequal slotted antenna is 45.12 dB, directivity is 6.54 dBi with the efficiency of 60 % and at 60 GHz, and the measurement value of 36.35 is observed which covers the complete RADAR applications which have an unlicensed bandwidth. The dimension of tree-shaped unequal slotted antenna is observed as 12*7*0.508 mm3. The proposed tree-shaped unequal slotted antenna is well suited for millimeter-wave appliances such as Microcell, Femtocell and macrocell applications because of its good bandwidth and less dimension. [ABSTRACT FROM AUTHOR]

For the physical model testing of wave energy converters (WECs) in the wave basin, it is necessary to test the models in a small number of sea states. Previously, the H – T binning method was widely used to determine the sea states that are representative of an ocean area. However, it omitted much useful information such as the wave directionality. In this paper, a novel method, the K -means clustering technique is used in combination with High Frequency (HF) radar measured data from Wave Hub, UK. The results show that K -means clustering method better preserves the characteristics of the ocean area than the binning method. Furthermore, the impact of different regrouping methods on assessing the annual energy output of the model is investigated, by applying the K -means clustering method to a 1:25 two-body hinged raft WEC. It is found that although non-linear performance can be clearly observed in the model both physically and numerically. Due to the fact that most sea states from Wave Hub are out of the non-linearity range of the model, the non-linear effect on the overall performance of the WEC model in this ocean area is limited. It allows the annual energy output to be accurately predicted by using only a small number of representative sea states (defined as K) ≤15, based on K -means clustering method. • K -means method selected representative sea states tested on a physical WEC model. • K -means method is effective in selecting the sea states for WEC model testing. • Representative sea states can obtain accurate annual energy output estimation. • Non-linearity of WEC tested had limited influence on annual energy output estimation. [ABSTRACT FROM AUTHOR]

This study presents the analysis of planetary waves (PWs) using daily mean wind velocities for four years (August 2013 to July 2017) of continuous measurements using MF radar over the low latitude Indian region Kolhapur (16.8° N; 74.2° E). The MF radar at Kolhapur was upgraded in 2013. These are the first results of PWs after the upgradation of MF radar. The seasonal and intra-seasonal variabilities of East-West (EW) traveling PWs in the MLT region have been studied. In the present work, the data was analyzed to study the waves with various periodicities (e.g. 3–4, 5–8, 15–17, and 30–60 days). The 3.5 day [Ultra-Fast Kelvin (UFK)] wave shows semiannual variability with burst like wave activity observed during the summer months and December solstice. In addition, it is observed to be stronger in the spring equinoctial period. A strong semiannual oscillation (SAO) has been observed in a 6.5-day wave with peaks near the equinoxes. Similar to SAO over the low latitude MLT region, the wave activity is stronger in April/May than in September/October. The 6.5-day waves are observed to be stronger when the background mean wind is westward. From the analysis, it has been seen that the period before and after the equinoctial period is favorable for the 6.5-day wave propagation. The 16-day wave has no significant seasonal dependence; instead, the waves spread to almost all seasons. The Madden-Julian Oscillations (MJOs) have been observed to be propagating with an average wind speed of ∼ 5 m/s when the background mean wind is eastward. The occurrence of MJO is observed during the summer and winter months. These results are the first of their kind in two aspects: first, they show the PWs with enhanced altitude coverage covering up to 110 km, and second, they show the PWs not contaminated due to equatorial electro jet influence. [ABSTRACT FROM AUTHOR]

We describe the use of radar beam-park experiments to characterize the space debris resulting from a recent fragmentation event, the deliberate demolition of the defunct Kosmos-1408 satellite. We identify the Kosmos-1408 fragments and present distribution of measurement parameters as well as proxy orbit parameters. We present and apply a novel technique to estimate the size of objects by matching the signal to noise ratio of the detection to the radiation pattern of the radar. With this method we estimate the size distribution of the debris cloud. We also demonstrate how a pair of beam-park observations can be used to perform a crude, yet seemingly reliable, initial orbit determination. Finally, we present followup observations ∼ 5 months after the fragmentation that show a still compact cloud of debris. • The deliberate destruction of the Kosmos-1408 satellite has generated an appreciable cloud of space debris. • Ground-based radars in beam-park mode can be used to observe and characterize the debris cloud. • We have used these observations to estimate size distributions of the debris cloud. • Orbit information for objects can, in some cases, be obtained or updated using these kinds of observations. [ABSTRACT FROM AUTHOR]

Ground-based radar interferometry offers significant capabilities for the observation of engineering structures and natural objects displacements. The quality of the recorded displacement is significantly influenced by the intensity of the reflected radar signal. In order to determine the actual accuracy of measurement performed in the field, two comparative experiments were carried out. In both cases, referential values were specified using precise instruments: a laser interferometer and a precise total station. This way, the error value equal to 0.1–0.2 mm declared by the manufacturer was confirmed in the field conditions. Furthermore, the relationship between SNR (signal-to-noise ratio) parameter and the actual measurement accuracy was analysed based on the acquired results. Due to the different ways of expressing the parameter, i.e. thermal and estimated SNR values, specific for the applied radar system, both of them were analysed. Finally, the model which allows determining the actual accuracy of displacement measurement in the field was proposed. It includes the SNR value and the distance to the object, so the accuracy can be reliably estimated upon these basic parameters without the need for additional measurement techniques. [ABSTRACT FROM AUTHOR]

Insects are the most diverse group of animals on Earth, but their small size and high diversity have always made them challenging to study. Recent technological advances have the potential to revolutionise insect ecology and monitoring. We describe the state of the art of four technologies (computer vision, acoustic monitoring, radar, and molecular methods), and assess their advantages, current limitations, and future potential. We discuss how these technologies can adhere to modern standards of data curation and transparency, their implications for citizen science, and their potential for integration among different monitoring programmes and technologies. We argue that they provide unprecedented possibilities for insect ecology and monitoring, but it will be important to foster international standards via collaboration. Technological developments are opening new possibilities for biodiversity monitoring, but – especially for insects – they come with their own unique set of limitations. Due to the vast diversity of insects, of which at least 80% remain undescribed, traditional monitoring is unable to provide even basic knowledge of the state of most insect species in most places. We appraise four emerging tools and technologies (computer vision, acoustic monitoring, radar, and molecular methods) that provide unprecedented opportunities for insect ecology. These technologies can enhance spatial, temporal, and taxonomic coverage of monitoring, but none can monitor all insects at all scales, and each comes with a set of limitations. Technological integration, open data, and international standards are needed to harness the full potential of novel technologies for insect monitoring. [ABSTRACT FROM AUTHOR]

Based on a variety of observation instruments, we have comprehensively analysed the rare topside fossil plumes after sunrise during the recovery phase of the 27–29 May 2017 magnetic storm over Sanya. The results showed that the irregularities leading to these topside plumes on Sanya Very High Frequency (VHF) radar maps were not freshly generated after sunrise, but were able to survive at even ∼02:30UT (∼09:48LT). Different from the fresh equatorial plasma bubbles (EPBs) near sunrise, the | V d | of these plumes was very small and the zonal drift was also unnoticeable. Although a plasma depletion could be observed by Swarm A satellite near Sanya, it was too small and no ionospheric scintillation or TEC fast fluctuation was caused by it. Since the simultaneous disturbances were found under the F peak over Sanya and the corresponding plumes at Fuke appeared later than those at Sanya by ∼40 min, it was inferred that the irregularities leading to these topside plumes were generated somewhere to the south of Sanya, and then grew and reached higher altitudes and extended to higher latitudes along the geomagnetic field lines. Combining the theory of disturbance electric field during storm, it was inferred that the eastward overshielding penetration electric field as well as the uplift of F layer supported the formation and sustainment of the irregularities leading to the topside plumes. [ABSTRACT FROM AUTHOR]

This study evaluated feasibility and patient outcomes for targeted axillary lymph node (LN) dissection (TAD) with SAVI SCOUT® ultrasound-guided radar reflector localization (RRL). In this IRB-approved retrospective study, 800 consecutive patients who underwent ultrasound-guided RRL between November 2017 and June 2020 were reviewed. Of these patients, those with axillary LN RRL were included in this study. Reports in the electronic medical record were reviewed to determine RRL placement, retrieval, and surgical outcomes. A total of 147 patients met inclusion criteria. Of these, axillary RRL was performed for biopsy-proven metastatic disease in 134 and inconclusive or benign biopsy in 13. RRL was successful in 146/151 lymph nodes (97%). Two patients had placement >10 mm from target and 3 had no post-placement signal. In all 5, the targets were successfully retrieved at surgery. Specimen radiographs were performed in 135 cases and confirmed the intended target in all 135 (100%). In 109 patients who underwent TAD + sentinel lymph node biopsy (SLNB), the RRL LN and the SLN(s) were different in 18 (17%). In 3 of these, the RRL LN was the only malignant LN (3%). In the 105 patients who underwent neoadjuvant chemotherapy, 43% (45/105) achieved nodal pCR and 85% (89/105) had <3 metastatic lymph nodes at surgery. Ultrasound-guided RRL of axillary LNs is a feasible approach to facilitate TAD with high placement and retrieval success rates. This enables TAD as an alternative to complete axillary LN dissection (cALND), sparing some patients with low nodal tumor burden from cALND. • US-guided SAVI SCOUT® radar reflector localization of axillary lymph nodes is highly successful (97% initial placement success rate, 100% surgery retrieval success rate) • This facilitates targeted axillary dissection + sentinel lymph node biopsy in patients with high likelihood of achieving low nodal burden • For ER/PR+ patients with only 1 suspicious lymph node on initial imaging, 95% had low nodal burden after neoadjuvant chemotherapy Precis • US-guided SAVI SCOUT® radar reflector localization of axillary lymph nodes is highly successful and facilitates targeted axillary dissection in patients with a likelihood of low axillary nodal burden [ABSTRACT FROM AUTHOR]

• This work attempts to make an overview of the RA schemes for target tracking. • The modeling methods and solution techniques for RA in RSN are reviewed. • The challenges and promising research directions on RA are discussed. Traditional networked radar fusion technology adopts an open-loop signal processing manner, in which multiple nodes independently detect or track target first, and then send their raw data or processed measurements to the fusion center for target state estimation. In such a working manner, each radar sensor operates within predetermined rules, adopts fixed transmit and receiving mode for changeable target tracking environment, and thus will definitely cause an insufficient use of its limited resource. Resource allocation (RA) has emerged as a promising technology to exploit the limited radar resource in a more efficient way by allocating the available resource parameters w.r.t. multiple nodes collaboratively in view of the fused target tracking performance. The goal of this paper is to provide a brief overview of the RA methods for fused target tracking in radar sensor network. We mainly investigate the existing RA works and divide them into two types, namely tracking quality constrained RA type and performance driven RA type. Solution techniques for both types appeared in the literatures are also summarized. Finally, some potential future research directions in this field are discussed. [ABSTRACT FROM AUTHOR]

A recent paper (Mhaskar (2020)) introduces a straightforward and simple kernel based approximation for manifold learning that does not require the knowledge of anything about the manifold, except for its dimension. In this paper, we examine how the pointwise error in approximation using least squares optimization based on similarly localized kernels depends upon the data characteristics and deteriorates as one goes away from the training data. The theory is presented with an abstract localized kernel, which can utilize any prior knowledge about the data being located on an unknown sub-manifold of a known manifold. We demonstrate the performance of our approach using a publicly available micro-Doppler data set, and investigate the use of different preprocessing measures, kernels, and manifold dimensions. Specifically, it is shown that the localized kernel introduced in the above mentioned paper when used with PCA components leads to a near-competitive performance to deep neural networks, and offers significant improvements in training speed and memory requirements. To demonstrate the fact that our methods are agnostic to the domain knowledge, we examine the classification problem in a simple video data set. • We examine the pointwise error in approximation using least squares optimization based on the kernel presented in Mhaskar (2020). • The approximation error depends upon the data characteristics and deteriorates as one goes away from the training data. • The theory is presented with an abstract localized kernel, which can utilize any prior knowledge about the data being located on an unknown sub-manifold of a known manifold. • We demonstrate the performance of this kernel using a publicly available micro-Doppler data set, investigating the use of different preprocessing measures, kernels, and manifold dimension. • It is shown that the proposed method offers nearcompetitive performance to deep neural networks and significant improvements to speed and accuracy. [ABSTRACT FROM AUTHOR]

The rapid development of detection technology, the technology with radar infrared compatible stealth function has become one of the important ways to improve the survivability of weapons and equipment. However, the two stealth mechanisms of radar stealth and infrared stealth are mutually exclusive. In this work, a multilayer radar-infrared compatible stealth metamaterial is presented based on SiO 2 fiber reinforced aerogels skeleton (SFRAS). The prepared samples with bird 's nest microstructure showed good compressive strength (1.73–2.52 MPa) and low density (0.22–0.27 g/cm3), achieving lightweight. Moreover, the metamaterial exhibits excellent electromagnetic absorption performance, effective absorbing broadband (13 GHz), and ultra-wideband absorption of electromagnetic waves is achieved. Nanoporous structure and low thermal conductivity (0.03426–0.05011 W/ (m K)) successfully reduce the surface thermal radiation, indicating that it is a potential material for achieving infrared stealth. The new technology provides a new approach to the research of the radar-infrared compatible stealth structure. • A multilayer radar-infrared compatible stealth metamaterial is synthesized based on the traditional papermaking process. • The effect of fiber contents on both mechanical and thermal conductivity was studied. • The absorbing properties of metamaterial are studied, and the relative bandwidth reaches139.8 %. • The structure was observed to have a unique three-dimensional bird's nest-like structure by using SEM. [ABSTRACT FROM AUTHOR]

A composite hybrid structure reinforced by cobalt oxide (Co3O4), copper-copper oxide (Cu–Cu2O), and barium hexaferrite (BaFe12O19) was investigated. Chemical reduction and sol-gel were used for synthesizing reinforcement materials. Polyester resin was used as a matrix material. Synthesized powders were analyzed and characterized by using various characterization techniques such as differential thermal analysis, X-ray diffractions (XRD), vibrating sample magnetometer (VSM), scanning electron microscopy (SEM), and particle size analysis. Three-Layer RAM structures were prepared layer by layer, and the concentration of the filler powders was the same in each layer. RAM structures were investigated using a vector network analyzer (VNA). Based on the radar absorbing analysis, the most effective absorption is possessed by sample RA5 50 wt%, which consists of two layers of cobalt oxide and one layer of copper-copper oxide. The maximum value of the reflection loss was- 45 dB at a frequency of 10.25 GHz. • A composite hybrid structure reinforced with Co3O4, Cu–Cu2O and BaFe12O19 was produced by and sol-gel and chemical reduction. • Three-layer RAM structures were prepared with different additives. • Radar absorbing structures were investigated using a vector network analyzer (VNA). • Most effective absorption achieved by sample consisting of two layers of cobalt oxide and one layer of copper-copper oxide. • The maximum value of reflection loss was - 45 dB at a frequency of 10.25 GHz. [ABSTRACT FROM AUTHOR]

This study presents low phase angle 0 ° – 5 ° measurements of polarimetric properties of icy planetary regolith analog materials acquired using the custom-built Multi-Axis- Goniometer-Instrument (MAGI). We present same sense (S C) , and opposite sense (O C) backscatter circular polarization coefficients, circular polarization ratio (C P R) , and degree linear polarization (D L P) of spherical latex (non-dye) beads of varying sizes and volume concentrations (v/v) in aqueous solutions (λ = 0. 8 μ m) in water. We also present measurements of alumina powder in air at λ = 1. 064 μ m. Measurements showed that at a low incidence angle (i = 0 °) , backscatter is dominated by surface specular single-bounce scattering, that hides other scattering processes. At high (i = 15 °) incidence angle, surface single-bounce surface scattering becomes negligible, allowing for the detection of diffuse, dihedral (multiple bounces) scattering. We find that classical Mie alumina particles (2. 1 μ m , 4. 0 μ m) enhance subsurface scattering due to a larger void space relative to larger Mie particles (30 μ m) , that cause the radar signal to scatter forward off small imperfections, maintaining the polarization properties of the signal and generating high > 1 C P R. Latex beads, representing impurities, demonstrate the impact of isotropic and anisotropic scattering on radar signatures. This study also found that the scattering medium's anisotropy correlates to the size of the beads, while the void space of the medium inversely correlates with the bead size and the volume concentration (v/v) of the beads. Rayleigh beads, due to isotropic scattering from the reduced scattering cross-section and higher transparency relative to larger impurities, generate subsurface single bounce scattering from the sample platform, producing O C ≫ S C and a low (< 0. 5) C P R across all v/v. Rayleigh impurities in transparent water-ice simulate single bounce scattering from underlying layers. Conversely, classical and large Mie beads generate anisotropic scattering that intensifies scattering in the forward direction with high C P R , inversely proportional to the volume concentration. This study aids in interpreting radar observations of icy bodies in the solar system, providing insights into the interplay between radar waves and icy regolith compositions. • Multi-Axis-Goniometer-Instrument for measuring polarization at low phase angles. • Polarization properties of latex beads in aqueous solution and alumina powder in air. • Alumina particles of different sizes affect subsurface scattering due to void space. • Latex beads affect polarization through isotropic, and anisotropic scattering. • The study provides insights for interpreting radar observations of icy bodies. [ABSTRACT FROM AUTHOR]

The increasing use of Global Positioning System (GPS)-based autonomous drones in various civilian and military applications has raised concerns about malicious or unintentionally harmful activities that can be carried through them. It is necessary to detect these intruding drones within protected areas and prevent their unauthorized access by denying them entry. We propose a framework that combines the detection of intruding drones using an L-band radar and then counters by transmitting fake GPS coordinates toward the drones, effectively redirecting them. This article explains the setup required to add to an existing monostatic radar that provides two-dimensional information, i.e., range and azimuth information, to enable the proposed setup to get the elevation angle of the drone. We propose a linear array design using digital receive-only beamforming techniques in the elevation domain to compute the elevation angle in addition to the range, velocity, and azimuth information being provided by the monostatic radar to get complete information about the intruding drone. The simulation of drone detection is followed by an examination of the impact of transmitting fabricated GPS coordinates to the drone. Experimental verification has been conducted to validate both the digital beamforming algorithm and the spoofing technique. This approach blocks the reception of actual GPS signals in the drone and replaces the drone's GPS coordinates with alternative, desired coordinates. The proposed framework can be used to prevent unauthorized drone intrusions in the protected area. [ABSTRACT FROM AUTHOR]

Angle estimation of signals received by antenna arrays is a key step in adaptive beamforming, used to detect and locate targets in space. It is desirable to reduce costs by employing a smaller number of antennas while maintaining efficiency and degrees of freedom (DOF) of the system at the same time. Co-prime antenna arrays not only circumvent the operational constraints of cost and hardware complexity, but also boost the DOF by utilizing far fewer antennas as compared to traditional uniform linear arrays. In this paper, meta-heuristic computing paradigm for estimating arrival angle of targets with co-prime arrays incorporated in monostatic radar is proposed. The system's autocorrelation and Mean Square Error (MSE) are used for fitness function optimized by global/local search with Genetic Algorithm (GA) and Pattern Search (PS). Monte Carlo simulations are performed to evaluate the performance via estimation accuracy, MSE, and computational cost for varying numbers of impinging waves. [ABSTRACT FROM AUTHOR]

In this study, a novel RAM utilizing Fe 3 O 4 , ZnO, polyaniline (PANI), and reduced graphene oxide (rGO) in the form of nanohybrid is invented, namely Fe 3 O 4 /ZnO/PANI/rGO nanohybrid. In this study, the effects of the rGO fraction in Fe 3 O 4 /ZnO/PANI/rGO composition on the radar absorbing performance were investigated. Meanwhile, exploring the quality of the nanohybrid sample, such as the crystal structure, functional groups, morphology, magnetic properties, and reflection loss was also examined carefully. It shows that two crystalline phases of Fe 3 O 4 and ZnO, as well as amorphous structures of PANI and rGO are formed independently, indicating successful nanohybrid formation. In this case, PANI functioned as a binder for Fe 3 O 4 and ZnO, and thus, it could infiltrate the pores of rGO. Fe 3 O 4 /ZnO/PANI/rGO nanohybrid possesses superparamagnetic properties with decreasing saturation magnetization as rGO composition increases. Nevertheless, rGO enhanced the radar absorption performance with a maximum reflection loss of −8.57 dB at 11.10 GHz. In this present research, the synergy of combination between the magnetic and dielectric losses in the Fe 3 O 4 /ZnO/PANI/rGO nanohybrid is discussed together with plausible strategies to obtain highly efficient RAM. • The radar technology is one of important aspect in stealth technology. • One of the most popular magnetic materials applied as radar technology is Fe 3 O 4. • A novel Fe 3 O 4 /ZnO/PANI/rGO nanohybrid for radar absorbing application was successfully synthesized using the regular mixing method. • Radar absorbing material (RAM) must have several features, including high permittivity and permeability with high magnetic saturation. • rGO enhanced the radar absorption performance with a maximum reflection loss of −8.57 dB at 11.10 GHz. [ABSTRACT FROM AUTHOR]

This paper describes a ultra-wideband (UWB) three-stage cascaded high gain amplifier with low group delay variation for phased-array radar system. The shunt inductor at the input not only provides an electrostatic discharge (ESD) path to ground, but also introduces a new notch for S 11 , thus extending the matching bandwidth. Staggered tuning of load impedance peaks at each stage facilitates a balance between flat gain and low group delay variation. The output stage further enhances the overall gain while reinforcing bandwidth and stability through resistive feedback, and employs an adaptive bias circuit for linearity improvement. Implemented in SMIC 40-nm CMOS technology, the proposed amplifier achieves good input impedance matching, flat gain and low group delay variation of ±73.5 ps over 4.7–16 GHz. The whole power consumption is 198.3 mW and the output 1 dB compression point (OP 1dB) is greater than 9 dBm. After careful design, the chip size is 0.64 mm2. [ABSTRACT FROM AUTHOR]

Spatiotemporal prediction is a challenging topic because of uncertainty. Existing works attempt to design complicated systems to learn short-term and long-term dynamics. However, these models suffer from heavy computational burden on spatiotemporal data, especially for high-resolution frames. To reduce resource dependence, we propose FastNet, a novel and light encoder–decoder for predictive learning. We stack four ConvLSTM (Convolutional Long Short-Term Memory) based layers to construct a hierarchical framework. Based on this architecture, the feature aggregation module first aligns the temporal context, then decouples different frequency information, next gathers multi-level features and last synthesizes new feature maps alternately. We aggregate various and hierarchical features into predictions bringing two benefits: rich multi-level features and low resource usage. As for the unit blocks, depth-wise separable convolution is used to improve model efficiency and compress model size. Besides, we adopt perceptual loss as the cost function between ground truths and predictions, which helps our model to get higher similarity with true frames. In experiments, we evaluate the performances of FastNet on the MovingMNIST (Mixed National Institute of Standards and Technology) and Radar Echo datasets to verify its effectiveness. The quantitative metrics on the Radar Echo dataset show that FastNet reaches a slight increase in accuracy but up to 84% decline in computation compared with PredRNN-V2. Therefore, our FastNet achieves competitive results with lower resource usage and fewer parameters than the state-of-the-art model. [ABSTRACT FROM AUTHOR]

Recent studies have shown that radar temporal coherence over tropical and boreal forests undergoes a diurnal cycle as a result of a combined effect of the wind-induced motion of scatterers and of the change and displacement of water within the plant in response to the transpiration process. Within this context, the objective of this paper is to investigate, for the first time, the diurnal cycle of temporal coherence over wheat crops in relation to its development and physiological functioning throughout the agricultural season. A ground-based experiment was installed in Morocco, targeting a wheat field during the 2020 agricultural season. The radar system, essentially based on a Vector Network Analyzer (VNA) connected to 6C-band antennas installed at the top of a 20 m tower, has enabled quad-polarimetric acquisitions every 15 min. In parallel, evapotranspiration, soil moisture and meteorological variables are automatically measured in addition to above-ground biomass and vegetation water content collected during field campaigns. The results show that the temporal coherence with a 15 min baseline follows a marked diurnal cycle characterized by variable amplitude according to the phenological stage, with high values during the night, a significant morning drop to reach the lowest values in the late afternoon followed by an increase to recover the high nighttime values. The rate of the drop at dawn is shown to be related to the increase of evapotranspiration (r = 0.80 at VV polarization) when the wheat is covering the soil and the transpiration dominate the evapotranspiration process. This supports the assumption of a physiological effect related to water movement entailing a decorrelation. By contrast, the daily minimum of temporal coherence occurring in the late afternoon correlates well to the daily maximum of wind (r = 0.7). Interestingly enough, the amplitude of the diurnal cycle exhibit a marked seasonal evolution characterized by an increase of 85% from tillering to maturity in relation to the wheat development. At the early start of the season when the soil is almost bare, irrigation events impact slightly the diurnal cycle of temporal coherence. Likewise, it is shown that the presence of dew in the early morning has led to a decrease of the decorrelation rate. Temporal coherence dynamic has also been investigated for longer baselines up to 22 days. Results indicate a stronger decorrelation than what has been observed on tropical and boreal forests by previous studies with values below 0.4 for baselines above 2 days. Taken together, the results of this work demonstrate the unique potential of sub-daily C-band data for monitoring crop water status by future geostationary radar missions such as Hydroterra. • Diurnal cycles of 15-min C-band temporal coherence over wheat crops are analyzed. • The morning drop of the temporal coherence is related to the transpiration process. • Temporal coherence exhibits a marked seasonal dynamic according to phenological stages. • Irrigation events and morning dew have an impact on sub-daily temporal coherence. • Early morning hours showed potential for monitoring the vegetation physiological functioning. [ABSTRACT FROM AUTHOR]

Airspace surveillance is a significant issue for many countries to control and manage their airspace. The number of radars used and their coverage rate are the main issues to consider in this case. Therefore, this paper addresses the problem of finding the best radar locations to obtain the highest coverage rate with the least possible number of radars in a certain region. The radar placement problem is considered as a multi-objective optimization problem with two objectives: the number of radars and the coverage rate. To perfectly solve this optimization problem, a set of multi-objective meta-heuristic approaches based on simulated annealing, memory-based steady-state genetic algorithm, a decomposition-based multi-objective algorithm with differential evolution, and non-dominated sorting genetic algorithm (NSGA-II) are utilized. Algorithms are tested on a dataset created using DTED-1 map elevation data for two different selected regions. Based on the results, the NSGA-II algorithm achieves the best results and the highest coverage ratios among the tested algorithms. Two improved versions of the NSGA-II algorithm are also proposed to enhance its performance and make it more suitable for solving this optimization problem. The experimental results show that a coverage rate of 98% could be achieved with a small number of radars, and by increasing the number of radars, it exceeds 99%. • This paper solves the radar placement problem using a set of metaheuristic approaches. • The problem is considered as a multi-objective optimization problem. • Two adaptive and enhanced versions of the NSGA-II algorithm are proposed. • The results show that a coverage rate of 98% can be achieved with just a few radars. [ABSTRACT FROM AUTHOR]

The current study utilizes the operational data assimilation system of Deutscher Wetterdienst (DWD) to investigate the impacts of improved radar forward operator. First of all, it is shown that for experiments in which both conventional and radar data are assimilated and the latent heat nudging (LHN) is applied, the one with improved operator (i.e., with improved Mie-scattering scheme and accounting for beam broadening effect and etc.) exhibits neutral impacts on short-term forecasts. However, in subsequent experiments, in which conventional data are not assimilated and the LHN is switched off, the one with improved operator not just reduces representation error during data assimilation cycles but also enhances the short-term forecast skills. In addition, it is found that the subsequent experiments result in much shorter observation error correlation length scales for radar reflectivity data, indicating that the application of the LHN or assimilation of conventional data may increase the length scales. • Improved radar forward operator configurations reduce representation error but exhibit neutral impact on short-term forecasts • However, in the pure radar data assimilation experiment, improved operator configurations enhance forecast skills • The observation error statistics estimated by the Desroziers method exhibit clear dependency on the data assimilation [ABSTRACT FROM AUTHOR]

• U-Net and its improved models were used for radar echo extrapolation and precipitation nowcasting. • The nowcasted precipitation was used as input to the HEC-HMS hydrological model for flood forecasting. • Nested-Unet and U-Net 3Plus were helpful to improve the accuracy of precipitation nowcasting and flood forecasting. Accurate and timely short-term precipitation nowcasting is important for achieving reliable flood forecasting. The data-driven approaches have performed well in radar echo extrapolation to nowcast precipitation. In this paper, U-Net and its improved models, including SmaAt-Unet, Nested-Unet, and U-Net 3Plus were applied to perform radar echo extrapolation and precipitation nowcasting for 0.5 h, 1 h, and 2 h lead times of typical rainfall processes. The nowcasted precipitation was used as input to the HEC-HMS hydrological model for flood forecasting to compare the effect of different structural improvements to U-Net on the accuracy of flood forecasting. The results demonstrated that Nested-Unet and U-Net 3Plus aided in enhancing the accuracy of the extrapolation of moderate intensity radar echoes. With fewer discrepancies and better correlation with measured rainfall, the U-Net and U-Net 3Plus precipitation nowcasting results also produced improved flood forecasting outcome. The precipitation nowcasting and flood forecasting for SmaAt-Unet were slightly worse than other models; the relative errors of both flood peak and depth for Nested-Unet at 0.5 h lead time were less than 20 %, showing a good performance. Moreover, in a separate control experiment, the accuracy of the echo extrapolation was significantly decreased when convolutional block attention module (CBAM) was added to each model. However, all models have better extrapolation accuracy than the basic ConvLSTM. In general, Nested-Unet and U-Net 3Plus were helpful to improve the accuracy of precipitation nowcasting and flood forecasting, and the forecasted flood with 0.5 h and 1 h lead times could match the actual flood processes, but the peak discharge from nowcasting with 2 h lead time were severely underestimated, while the peak occurrence time could be forecasted correctly. These conclusions and attempts can provide effective guidelines for regional precipitation nowcasting and flood forecasting. [ABSTRACT FROM AUTHOR]

• This paper aims to measure the electromagnetic (EM) characteristics of 3D-printed radar absorbing structures (RASs) based on three-dimensional period pattern surface. • The metrology is validated using HFSS software, a 3D printer and a scanning free-space measurement. • It is crucial to employ specific measurement conditions for each surface shape and examine the distribution of EM characteristics across the entire specimen area. • The analysis and measurement techniques proposed can be applied to the design of 3D-printed RASs. This paper aims to assess the electromagnetic (EM) characteristics of 3D-printed radar absorbing structures (RASs) based on three-dimensional period pattern surface (3D PPS) within the X-band frequency range (8.2–12.4 GHz). The assessment is validated through HFSS software, a 3D printer (Markforged, X7), and a scanning free-space measurement (SFM) system. Firstly, the analysis indicates that the EM characteristics of RASs based on 3D PPS are impacted by impedance matching in the thickness direction and the scattering of EM waves at the edges. The utilization of Onyx (Chopped carbon fiber/Nylon) reveals variations in resonance frequencies and EM wave absorption performance contingent upon the surface shape. Furthermore, significant differences in the variations of EM characteristics are observed even for RASs with the same surface shape but different materials. Secondly, the measurement results of 3D-printed RAS specimens based on PPS using Onyx exhibit similar trends to the analysis results obtained with the SFM system. Ensuring precise measurement results requires specific measurement conditions tailored to each surface shape, along with an examination of the EM characteristic distribution across the entire specimen area. This is crucial due to variations in the size, number, and range of reflected EM waves in the time domain. The analysis and measurement techniques presented in this study hold applicability in designing 3D-printed RASs that demand high EM wave absorption performance, whether under normal or oblique incident EM waves. [ABSTRACT FROM AUTHOR]

Non-cooperative Sense and Avoid is a critical technology for the safety and autonomy of Unmanned Aerial Vehicles (UAV). Standalone sensing solutions, i.e., only based on either visual cameras or radars, encounter challenges especially for vehicles flying at low altitude. To overcome this limit, sensor fusion strategies can play a key role. In this framework, this paper proposes a two-step radar/visual sensor fusion approach taking place both at detection and tracking level. The first step, named "Fuse-Before-Track", consists in jointly using radar information and visual detections (provided by Convolutional Neural Network-based detectors) to remove uninteresting radar echoes thus improving ground clutter removal and speeding up the radar processing pipeline. At the second level, tracking takes place by exploiting the previously retrieved (confirmed) radar measurements and fusing visual detections to improve the solution accuracy. The proposed approach is tested on data collected during experimental flight tests where a ground-fixed multi-sensor setup (integrating a low size weight and power radar and a daylight camera) is used to detect and track a small UAV manually piloted to carry out approaching manoeuvres. Detection and tracking performance is assessed using, as a benchmark, a cm-level relative positioning solution retrieved by means of Carrier Phase Differential GNSS techniques. The implemented detection-level fusion approach ensures radar detection accuracy of meter level and meter-per-second level on range and range rate, respectively. In addition, the second level of fusion allows attaining sub-degree level errors in the angular and angular rates estimates at a tracking stage. Tracking data are finally used for conflict threat assessment, i.e., to get estimates of the distance and time at closest point of approach, with mean errors on the former of about 10 m in most encounters when the latter falls below 50 s. [ABSTRACT FROM AUTHOR]

In this paper, we introduce a groundbreaking modification to a K-band substrate integrated waveguide (SIW) Longitudinal Slot Array Antenna for Vehicle-to-Everything (V2X) applications, particularly long-range radar (LRR) in the automotive industry. Our approach harnesses an elliptic metasurface capable of distinguishing between TE and TM modes in relation to radiation direction. By utilizing metasurfaces, we effectively address the issue of mutual coupling between antenna elements, which often results in subpar antenna performance. This modification focuses on improving various antenna characteristics, including frequency bandwidth (expanded by approximately four times), sidelobe level (reduced by 4 dB), aperture efficiency (increased to about 44%), and cross-polarization (reduced by an average of 10 dB). In essence, the results demonstrate that the increased number of longitudinal elements can be effectively enhanced by utilizing the metasurface structure, while maintaining an acceptable level of efficiency. As an illustrative case, we design a 1 × 32-element Longitudinal Slot Array Antenna using the Elliott method operating at 24.3 GHz, with the antenna size measuring 12.5 × 154 mm 2. Experimental measurements validate our design, showcasing a 10 dB return loss bandwidth of 24.05–24.45 GHz, a maximum gain of 14.45 dBi, a sidelobe level of 24.5 dB, cross-polarization exceeding 30 dB, and an impressive aperture efficiency of 65%. [ABSTRACT FROM AUTHOR]

We present a novel joint radar and communication (JRC) system that utilizes a chaotic optoelectronic oscillator (OEO) to generate a wideband radio frequency carrier. By mixing the carrier with an on-off keying (OOK) signal through intensity modulation and direct detection, a wideband JRC waveform is generated. One part of the waveform is used for transmitting, while the other serves as a reference for radar reception. The unique properties of the chaotic OEO signal, such as its randomness and large bandwidth, are leveraged to achieve superior system performance and eliminate the need for an electronic arbitrary waveform generator. In the proof-of-concept experiment, the JRC system achieves a radar range resolution of 7 cm and a wireless communication rate of 125 Mbit/s. [ABSTRACT FROM AUTHOR]

The recently developed frequency diverse array (FDA) radar applies a small frequency increment across the array elements, which provides advantages in clutter suppression, jamming suppression, and target detection for existing radar systems. In this paper, the frequency increment is enlarged to guarantee that the transmit waveforms are orthogonal in frequency domain for multiple-input multiple-output (MIMO) radar. A multi-scale moving target detection method of FDA-MIMO radar is proposed. The FDA radar with a large frequency increment suffers from the deteriorated decorrelation of scatterers within the same range bin and causes the inner-bin range dependence (IRD) property in transmit spatial domain. By taking additional space–time snapshots in transmit domain as training samples, the space–time adaptive processing (STAP) is applied in joint receive and Doppler domain for clutter suppression, which alleviates the requirement of insufficient training samples in non-stationary clutter environment. In the sequel, a set of beamformers within the whole angular domain of interest is utilized for target detection, which achieves target detection under the condition of random target locations and sizes. Numerical simulation results are provided to verify the effectiveness of the proposed method. • FDA radar of large Δ f can realize waveform orthogonality and obtain range DOFs. • FDA of large Δ f improves the range resolution to distinguish inner-bin scatterers. • The proposed STAP method alleviates the pressure on insufficient training samples. • A set of beamformers are designed to detect target with random locations and sizes. [ABSTRACT FROM AUTHOR]

In this paper, we propose a joint transmit and receive antenna selection scheme for frequency diverse array (FDA) radar that aims at finding an optimal selection of employed FDA antennas, formed by minimizing the Cramér–Rao lower bound (CRLB) of the target localization problem given the available a priori knowledge of potential target locations. The resulting problem is a non-convex Boolean problem in which the objective function is a quadratic objective function with respect to the optimization variables. To allow for an efficient solution, an iterative relaxed algorithm is proposed, substantially simplifying the resulting minimization. Numerical simulations are provided to demonstrate the effectiveness of the proposed approach. • The joint transmit and receive antenna selection scheme for frequency diverse array (FDA) radar is investigated. • The antenna placement is formed by minimizing the Cramér–Rao lower bound (CRLB) of the target localization problem. • An iterative relaxed algorithm is proposed for the resulting non-convex Boolean problem. [ABSTRACT FROM AUTHOR]