Simultaneous Radar Research Articles

First holistic modelling of meteoroid ablation and fragmentation: A case study of the Orionids recorded by the Canadian Automated Meteor Observatory

18 mm-sized Orionid meteoroids were captured in 2019 and 2020 by the Canadian Automated Observatory’s mirror tracking system. Meteor position measurements were made to an accuracy of ∼1m and the meteors were tracked to a limiting magnitude of about +7.5 at the faintest point. The trajectory estimation shows the intrinsic physical dispersion of the Orionid radiant is 0.400°±0.062°. An erosion-based entry model was fit to the observations to reproduce ablation and fragmentation for each meteor, simultaneously reproducing the light curve, the dynamics, and the wake. Wake observations were found to directly inform the grain mass distribution released in the modelled erosion. A new luminous efficiency model was derived from simultaneous radar and optical observations and applied in the modelling to improve its accuracy. The results show that the apparent strength of Orionids varies with radiant location and time of appearance during the period of shower activity. The average differential grain mass distribution index was 2.15, higher than found from in-situ estimates, possibly due to the evolution of the physical properties of meteoroids since ejection. All Orionids showed leading fragment morphology which was best explained by stopping the erosion at the peak of the light curve, leaving a non-fragmenting meteoroid with ∼10% of the original mass. The inverted Orionid meteoroid average bulk density of ∼300kgm−3, corresponding to porosities of ∼90%, is consistent with in-situ measurements of larger dust particles by Vega-2 at 1P/Halley and Rosetta at 67P.

Vigilance end-spurt patterns in event-related potentials

The end-spurt effect, where performance declines with time-on-task and then increases toward the end of a task, has garnered little attention in the vigilance literature. Researchers have suggested the performance enhancement is due to increased motivation or arousal with knowledge of the end of the vigil. However, recent examination of neural signature patterns during a simultaneous discrimination task, where task length was unknown, provided preliminary support that the end-spurt reflects pacing of resources. The current effort expands this previous work to an additional simultaneous task and to a successive discrimination task across two sessions, one where task length was not known and one where task length was known. Twenty-eight (Study 1) and a separate 24 (Study 2) participants completed a Simultaneous Radar task (Study 1) in one session and Simultaneous and Successive Lines tasks (Study 2) across two sessions while neural data was collected. Several event-related potentials exhibited non-monotonic patterns during the vigilance tasks, in some cases reflecting end-spurt patterns, but more commonly reflecting higher-order polynomial patterns. These patterns were more prevalent in anterior regions as opposed to posterior regions. Of note, the N1 anterior exhibited consistent general patterns across all the vigilance tasks and across sessions. Importantly, even when participants had knowledge of session length, some ERPs still exhibited higher-order polynomial trends, suggesting pacing rather than an end-spurt from motivation or arousal as the vigil ends. These insights can help inform predictive modeling of vigilance performance and the implementation of mitigation efforts to allay the vigilance decrement.

The Spectrum and Orbit of a Fireball Producing Mesospheric Irregularity and Implications for Meteor Mass Deposition

The physical properties of meteoroids producing meteor plasma non-field-aligned irregularities (NFAI) in the Earth’s atmosphere are poorly known. Here we report a complete picture of a fireball and mesospheric NFAI that it produced for the first time. Simultaneous radar and optical observations were made by the recently completed facility, Meteor and ionospheric Irregularity Observation System. The observations show that the mesospheric NFAI were clustered into three patches where the optical meteor flares took place, instead of being generated continuously along the whole meteor path. It is very likely that nanometer-or-larger-sized dust particles could be directly generated via meteoroid fragmentation at the flaring points and thus promote the generation of NFAI patches. The properties of the parent meteoroid show a chondrite type and a Jupiter family comet orbit, with Na/Mg and Fe/Mg intensity ratios of 1.5 and 1, respectively, photometric mass of about 4 g, and fragmentation strengths of around 10–74 kPa. The results suggest that the direct generation of dust particles, which was previously observed in the atmospheric disintegration of a kiloton-scale meteoroid, could be extended to the much smaller gram-scale meteoroids. Since meteoroids having such characteristics or more fragile material are not unusual, further studies leading to a better understanding of meteor mass deposition in the upper atmosphere, which consider the dust particles directly generated via gram-scale meteoroid fragmentation, are extremely important.

Spurious Beam Suppression in Dual-Beam Phased Array Transmission by Impedance Tuning

A significant challenge for dual-beam, codesigned systems, such as for simultaneous radar and communications transmission, has been identified as the spurious beams produced by spatial intermodulation from nonlinearities in the transmitter power amplifier. We demonstrate that tuning the load impedance of the power amplifiers can reverse the elementwise power amplifier nonlinear distortion, reducing the magnitude of the unwanted beam transmissions and restoring the integrity of the dual-beam antenna pattern for application to an active electronically scanned array. A comparison to a recently documented predistortion approach for correcting spurious transmissions is provided, and it is shown that impedance tuning can address both element output power and linearity, whereas predistortion addresses only the linearity issue and causes the amplifier gain in many of the array elements to suffer. For multiple dual-beam angle scenarios, simulation results show that impedance tuning is effective at maximizing beam power in both beam directions, maximizing current gain in the element power amplifiers, and minimizing the size of the unwanted spurious beams.

Formation of a Receiving Beam in a Receiving and Transmitting Phased X-Band Antenna Arrays for Tracking a Group of Targets at Close Distances with Simultaneous Radar Illumination

Formation of a Receiving Beam in a Receiving and Transmitting Phased X-Band Antenna Arrays for Tracking a Group of Targets at Close Distances with Simultaneous Radar Illumination

Spatial X-ray detection system based on simultaneous communication and radar

An integrated scheme of X-ray communication and detection is proposed in this paper, which is used for the detection of the unknown target inside the coating while communication. In contrast to the X-ray communication methods reported previously, simultaneous communication and radar detection have two distinct features. One is that both communication and detection signals share the same X-ray source and channel, so the spatial resources can be effectively utilized. The other is that X-ray can penetrate the metal shielding structure and detect the internal materials effectively. In order to achieve the above goals, the propagation feasibility of an X-ray signal in space and space sparse plasma environment are first analyzed. Simulation and experiment results indicate that the X-ray carrier can realize transmission without attenuation in space environment. Then, an X-ray radar and communication demonstration system is built to verify the detection ability of coated materials. Experimental results show that when the characteristic spectrum value of the unknown target is much higher than that of the rest shell, the spatial X-ray radar system can achieve more accurate discrimination. Finally, a conclusion is reached, and some feasible detection suggestions are provided for this simultaneous detection and communication system.

Why we need radar, lidar, and solar radiance observations to constrain ice cloud microphysics

Abstract. Ice clouds and their effect on earth's radiation budget are one of the largest sources of uncertainty in climate change predictions. The uncertainty in predicting ice cloud feedbacks in a warming climate arises due to uncertainties in measuring and explaining their current optical and microphysical properties as well as from insufficient knowledge about their spatial and temporal distribution. This knowledge can be significantly improved by active remote sensing, which can help to explore the vertical profile of ice cloud microphysics, such as ice particle size and ice water content. This study focuses on the well-established variational approach VarCloud to retrieve ice cloud microphysics from radar–lidar measurements. While active backscatter retrieval techniques surpass the information content of most passive, vertically integrated retrieval techniques, their accuracy is limited by essential assumptions about the ice crystal shape. Since most radar–lidar retrieval algorithms rely heavily on universal mass–size relationships to parameterize the prevalent ice particle shape, biases in ice water content and ice water path can be expected in individual cloud regimes. In turn, these biases can lead to an erroneous estimation of the radiative effect of ice clouds. In many cases, these biases could be spotted and corrected by the simultaneous exploitation of measured solar radiances. The agreement with measured solar radiances is a logical prerequisite for an accurate estimation of the radiative effect of ice clouds. To this end, this study exploits simultaneous radar, lidar, and passive measurements made on board the German High Altitude and Long Range Research Aircraft. By using the ice clouds derived with VarCloud as an input to radiative transfer calculations, simulated solar radiances are compared to measured solar radiances made above the actual clouds. This radiative closure study is done using different ice crystal models to improve the knowledge of the prevalent ice crystal shape. While in one case aggregates were capable of reconciling radar, lidar, and solar radiance measurements, this study also analyses a more problematic case for which no radiative closure could be achieved. In this case, collocated in situ measurements indicate that the lack of closure may be linked to unexpectedly high values of the ice crystal number density.

Simultaneous Radar Detection and Frequency Measurement by Broadband Microwave Photonic Processing

Incorporating radar detection and frequency measurement functions within a single system is highly desirable in modern RF applications. In this article, a microwave photonic system is proposed and demonstrated to simultaneously realize broadband radar detection and frequency measurement. By sharing a light with ± 2nd-order linear frequency-modulated (LFM) sidebands in a polarization-division-multiplexing manner, radar detection and frequency measurement functions can be realized simultaneously. In the transmitter, the shared light is used to generate a radar signal that has a quadrupled bandwidth compared with the input electrical LFM signal. In the receiver, the shared light is applied as the reference to perform photonic de-chirping of the radar echo and to scan the frequency of the signal under test (SUT) along two orthogonal polarization directions. In the experiment, a 4.5–6.5 GHz LFM signal is used to generate the shared light source, based on which radar detection (bandwidth: 18–26 GHz) with a range resolution as high as 2.06 cm, and frequency measurement (measurement range: 28–36 GHz) with a scanning rate of 0.8 GHz/μs and a resolution of 37.6 MHz are achieved. In addition, the reconfigurablilty of the frequency measurement range, and its capability for measuring the multi-tone and wideband signals are also demonstrated.

Antenna Element Index Modulation for Frequency Diverse Array

In this paper, we propose a new architecture and provide performance analysis for frequency diverse array (FDA) Radar combined with the index modulation (IM) techniques. Here, the IM concept is applied upon frequency offsets in an FDA. Information is transmitted by a dynamically selected subset of antenna element indices applying predefined carrier frequency offsets, which generate different radiation patterns. It is shown that this enables the capability for simultaneous wireless communication and FDA Radar that has the range-angle coupling issue resolved.

Relationships between the Structure of Convective Clouds and Lightning Frequency Derived from Radiophysical Measurements

The results of simultaneous radar, radiometric, and lightning location measurements are analyzed to reveal interrelations between the characteristics of electric discharges and the parameters of a cumulonimbus cloud developing near Saint Petersburg. The dependences of the cloud electric activity on the radar characteristics as well as on the parameters derived from the Meteosat SEVIRI radiometer measurements are considered. It is found that lightning frequency highly correlates with the volume of supercooled cloud regions with high values of reflectivity. An increase in the lightning frequency occurs about 20 minutes after the moment when supercooled cloud volumes with reflectivity above 35–55 dBZ reach the maximum values. The maximum precipitation flux precedes the maximum lightning frequency.

Physical properties of the meteoroids using simultaneous radar and optical observations

The calculation results of photographic and radar meteoroid mass of simultaneous radio - TV and radio-photographic observations of meteors in 1977–1980 in Hissar Astronomical Observatory of the Institute of Astrophysics, Academy of Sciences of Tajikistan. The analyses' results of the shape of light curves of meteors within the theory of evaporation and the theory of the quasi-continuous fragmentation are presented.The photographic meteoroid mass from the light curve were defined: a) by the value of maximum luminous intensity at a height hm and b) by the integration light curve. Based on analysis of the data of the photographic mass were obtained correction factor that takes into account the effect of fragmentation and other factors to determine the mass of meteoroids first method. Average value of the mass of meteoroids calculated from the light curve for meteors with magnitude M ≤ 1 is 19∗10−3g, and the average value of the mass found on magnitude of the luminous intensity at the height the maximum brightness consist 18.2∗10−3g, that is in satisfactory agreement between. Masses of the meteoroids was calculated also radio method by value of maximum linear electron density at the height of maximum ionization.In the framework of the classical theory and the theory quasi-continuous fragmentation, we analyzed the shape of the light curves of simultaneous radio - optical meteors. It is shown that the main mechanism of ablation approximately 60% of simultaneous radio - optical meteors is a quasi-continuous fragmentation. The bulk density and porosity of showers and sporadic meteoroids were determined. Found that the Geminids meteoroids and S.δ-Aquariids have the largest bulk densities (δ0=3.6g/cm3), and have not porosity (K = 0). A meteoroids of the showers Orionids and Leonids have the lowest bulk density (δ0≤0.6g/cm3), and the highest value of the porosity (60≤K≤80%). The mass fragments of shower and sporadic meteoroids lie in the range of 5∗10−8÷10−5g.

Dual-Use Multicarrier Waveform for Radar Detection and Communication

The use of multicarrier waveforms, such as orthogonal frequency division multiplexing (OFDM) as used in radio communication, is gaining interest within the radar community. This paper considers the optimization of radar performance within the structure imposed by a coded OFDM format required to achieve an acceptable communication link. The dual goal of achieving both satisfactory radar and communication performance raises challenges that can be substantively addressed by combining phase coding and modulation techniques to provide the temporal and spectral structure necessary to implement simultaneous radar and communication operations.

Waveform design for communicating radar systems using Fractional Fourier Transform

A novel waveform design technique for enabling a communication channel within a pulse radar is presented. The proposed waveform is composed of quasi-orthogonal chirp sub-carriers generated by means of the Fractional Fourier Transform (FrFT), with the aim of preserving the radar performance of a typical Linear Frequency Modulated (LFM) pulse while embedding data to be sent to a cooperative system. Waveform generation and demodulation are described, together with techniques aimed at optimising the design parameters and mitigating the Inter-Carrier Interference (ICI) caused by the quasi-orthogonality of the chirp sub-carriers. The proposed FrFT based communicating-radar (CoRadar) waveform design is compared with Orthogonal Frequency Division Multiplexing (OFDM) based CoRadar with respect to both radar and communication operations. Radar performance is evaluated through examination of the Ambiguity Function (AF) and by assessing the performance of a standard square law detector. Communication performance is shown in terms of Bit Error Ratio (BER) for different channel conditions. Results demonstrate that the proposed FrFT waveform presents performance close to a LFM pulse in terms of probability of detection and probability of false alarm, in exchange for slightly worse range and Doppler resolution. Furthermore, it is shown to maintain comparable communication performance with respect to the OFDM waveform. Finally, a hardware implementation is described that demonstrates the simultaneous radar and communication capabilities of the proposed system.

First results of optical meteor and meteor trail irregularity from simultaneous Sanya radar and video observations

Meteoroids entering the Earth's atmosphere can create meteor trail irregularity seriously disturbing the background ionosphere. Although numerous observations of meteor trail irregularities were performed with VHF/UHF coherent scatter radars in the past, no simultaneous radar and optical instruments were employed to investigate the characteristics of meteor trail irregularity and its corresponding meteoroid. By installing multiple video cameras near the Sanya VHF radar site, an observational campaign was conducted during the period from November 2016 to February 2017. A total of 242 optical meteors with simultaneous non-specular echoes backscattered from the plasma irregularities generated in the corresponding meteor trails were identified. A good agreement between the angular positions of non-specular echoes derived from the Sanya radar interferometer and those of optical meteors was found, validating that the radar system phase offsets have been properly calibrated. The results also verify the interferometry capability of Sanya radar for meteor trail irregularity observation. The non-specular echoes with simultaneous optical meteors were detected at magnetic aspect angles greater than ~78°. Based on the meteor visual magnitude estimated from the optical data, it was found that the radar non-specular echoes corresponding to brighter meteors survived for longer duration. This could provide observational evidence for the significance of meteoroid mass on the duration of meteor trail irregularity. On the other hand, the simultaneous radar and video common-volume observations showed that there were some cases with optical meteors but without radar non-specular echoes. One possibility could be that some of the optical meteors appeared at extremely low altitudes where meteor trail irregularities rarely occur.

Multi‐carrier radar waveforms for communications and detection

The use of multi-carrier waveforms, such as Orthogonal Frequency Division Multiplexing (OFDM) as used in radio communication, for radar operations has gained strong interest recently. While the authors have completed research on using multi-carrier waveforms for simultaneous radar and communications operations, this study focuses on the recent research on using these waveforms for communications. Namely, they demonstrate how to employ OFDM to modulate Multi-Frequency Complementary Phase Coded sequences for wireless communications.

Simultaneous Radar Observations of Vertical Profile of Rain Features from Space and Ground at Ku and Ka Bands at a Tropical Location

In this paper parameters of precipitation profiles obtained from precipitation radar aboard tropical rainfall measuring mission satellite and from ground based micro rain radar observations have been compared for different rain events. The dual frequency radar observations of precipitating atmosphere have been utilized to study the vertical profiles of radar reflectivity and rain rate. It is shown that the inclination of the ray path of the satellite borne radar significantly influences the rain rate measurements. The study demonstrates the efficacy of combining space borne and ground-based measurement in obtaining a complete profile of vertical rain structure.

Simultaneous Radar and Satellite Data Storm-Scale Assimilation Using an Ensemble Kalman Filter Approach for 24 May 2011

Abstract Assimilating high-resolution radar reflectivity and radial velocity into convection-permitting numerical weather prediction models has proven to be an important tool for improving forecast skill of convection. The use of satellite data for the application is much less well understood, only recently receiving significant attention. Since both radar and satellite data provide independent information, combing these two sources of data in a robust manner potentially represents the future of high-resolution data assimilation. This research combines Geostationary Operational Environmental Satellite 13 (GOES-13) cloud water path (CWP) retrievals with Weather Surveillance Radar-1988 Doppler (WSR-88D) reflectivity and radial velocity to examine the impacts of assimilating each for a severe weather event occurring in Oklahoma on 24 May 2011. Data are assimilated into a 3-km model using an ensemble adjustment Kalman filter approach with 36 members over a 2-h assimilation window between 1800 and 2000 UTC. Forecasts are then generated for 90 min at 5-min intervals starting at 1930 and 2000 UTC. Results show that both satellite and radar data are able to initiate convection, but that assimilating both spins up a storm much faster. Assimilating CWP also performs well at suppressing spurious precipitation and cloud cover in the model as well as capturing the anvil characteristics of developed storms. Radar data are most effective at resolving the 3D characteristics of the core convection. Assimilating both satellite and radar data generally resulted in the best model analysis and most skillful forecast for this event.

원거리에서 측정 가능한 호흡 및 심박 수 측정을 위한 도플러 레이더 시스템

본 논문에서는 원거리에서 사람의 호흡 및 심박수를 측정할 수 있는 Ku-Band 대역의 도플러 레이더 시스템을 설계하였다. 레이더로 측정을 하는 동시에 ECG(Electrocardiogram)를 이용하여 호흡 및 심박수 측정을 하였다. 수신된 I/Q(Inphase & Quadrature-phase) 신호를 이용한 arctangent demodulation을 적용하였을 때 RMSE(Root Mean Square Error)값을 약 50 % 정도 개선시킬 수 있었다. CW(Continuous Wave) 도플러 레이더는 송수신단이 연속적으로 항상 열려 있기 때문에 송신안테나에서 수신 안테나로 누설되는 전력이 발생하게 된다. 출력 파워가 높아질수록 누설되는 전력은 시스템의 SNR(Signal-to-Noise Ratio)에 영향을 주게 된다. 따라서 본 연구에서는 원거리에서 감지가 가능하도록 누설 전력의 반대위상을 갖는 신호를 더해줌으로써 누설 전력으로 인한 수신단의 감도 저하를 최소화 시키는 기법을 적용하였다. 위의 leakage cancellation 기법을 적용하여 최대 35 m 거리 대상의 호흡 및 심박 수를 측정하였으며, 이와 비교하여 ECG 값에서 추출한 심박 수 값과 일치함을 볼 수 있다. This paper presents a Ku-Band Doppler Radar System to measure respiration and heart rate. It was measured by using simultaneous radar and ECG(Electrocardiogram). Arctangent demodulation without dc offset compensation can be applied to transmitted I/Q(In-phase & Quadrature-phase) signal in order to improve the RMSE(Root Mean Square Error) about 50 %. The power leaked to receiving antenna from the transmitting antenna is always generated because of continuously opening the transceiver of CW(Continuous Wave) Doppler radar. As the output power increase, leakage power has an effect on the SNR(Signal-to-Noise Ratio) of the system. Therefore, in this paper, leakage cancellation technique that adds the signal having the opposite phase of the leakage power to the leakage power was implemented in order to minimize the decline of receiver sensitivity. By applying the leakage cancellation techniques described above, it is possible to measure the heart rate and respiration of the human at a distance of up to 35 m. the heart rate of the measured data at a distance of 35 m accords with the heart rate extracted from the ECG data.

Tests of the SMAP Combined Radar and Radiometer Algorithm Using Airborne Field Campaign Observations and Simulated Data

A soil moisture retrieval algorithm is proposed that takes advantage of the simultaneous radar and radiometer measurements by the forthcoming NASA Soil Moisture Active Passive (SMAP) mission. The algorithm is designed to downscale SMAP L-band brightness temperature measurements at low resolution ( ~ 40 km) to 9-km brightness temperature by using SMAP's L-band synthetic aperture radar (SAR) backscatter measurements at high resolution (1-3 km) in order to estimate soil moisture at 9-km resolution. The SMAP L-band SAR and radiometer instruments are designed to provide coincident observations at constant incidence angle, but at different spatial resolutions, across a wide swath. The algorithm described here takes advantage of the correlation between temporal fluctuations of brightness temperature and backscatter observed when viewing targets simultaneously at the same angle. Surface characteristics that affect the brightness temperature and backscatter measurements influence the signals at different time scales. This feature is applied in an approach in which fine-scale spatial heterogeneity detected by SAR observations is applied on coarser-scale radiometer measurements to produce an intermediate-resolution disaggregated brightness temperature field. These brightness temperatures are then used with established radiometer-based algorithms to retrieve soil moisture at the intermediate resolution. The capability of the overall algorithm is demonstrated using data acquired by the airborne passive and active L-band system from field campaigns and also by simulated global dataset. Results indicate that the algorithm has the potential to retrieve soil moisture at 9-km resolution, with the accuracy required for SMAP, over regions having vegetation up to 5- kg/m2 vegetation water content. The results show a reduction in root mean square error of volumetric soil moisture (40% improvement in the statistics) from the minimum performance defined as the soil moisture retrieved using radiometer measurements re-sampled to the intermediate scale.

Wind Motions around the Tropical Cirrus Using Simultaneous Radar and Lidar Observations over Gadanki (13.45°N, 79.18°E), India

The present study describes variation of peak linear depolarization ratio (LDR) with wind around the cloud altitude using simultaneous observation of winds and cirrus cloud for the first time using Indian MST radar and polarization lidar co-located over a low latitude station Gadanki (13.7°N and 79.2°E). Three different cases of passage of the cirrus at different altitudes are noticed, one during a North-East monsoon day and other two during South-West monsoon days. The zonal wind below the cloud height has shown similar variation with LDR during 02 November 2006 and the meridional wind within the cloud height during 25 July 2007 and 08 June 2006 has shown opposite variation with LDR. Even though there is a significant increase in zonal wind due to the existence of tropical easterly jet (TEJ) above cloud height during 25 July 2007 and 08 June 2006, also, the vertical wind is found to be continuously varying during 25 July 2007 and it is upward dominant in the initial stage and is mostly downward in the later stage of observation on 08 June 2006, there is a slight descent in cloud altitude only during 25 July 2007. Thus, the wind above the cloud height alone may not affect the ascent/descent of the cloud top altitude. The potential temperature gradient is high within the cloud heights when the cirrus present near the cold point tropopause indicates the maximum air-mass mixing near the tropopause.