Head Echo Research Articles

Determination of Meteor Vector Velocity Using MU Interferometry Measurements of Head Echoes

A new method for measuring the vector velocity of meteoroids using meteor head echoes is proposed in this study. The lateral velocity is determined by utilizing the phase interference measurement between channels, while the radial velocity is obtained using a conventional Doppler frequency shift measurement. Compared to previous studies, this method does not require multi-site observations and can calculate the vector velocity of meteors in real-time. This paper provides the complete process for the inversion of the meteor vector velocity, detailing the analyzing process using MU radar head echo data. First, the MUSIC algorithm was used to estimate the DOA of the meteor target, which is a parameter required for lateral velocity measurement. Channel calibration is required before this estimation. Next, delay-Doppler matched filter processing was performed on each receiving channel’s data to determine the distance and radial velocity of the meteor target. Subsequently, the lateral velocity component was synthesized using the least squares method from the phase difference rate extracted from the matched filter output results of multiple channel pairs. Then, the vector velocity and trajectory of the meteor could be determined. The method was verified using MU radar head echo data. Different groups of channel pairs were selected for calculating the lateral velocity, and the results were found to be close, demonstrating the self-consistency of the method. Additionally, the calculated vector velocity is consistent with the direction and magnitude of the meteor’s motion trajectory, confirming the feasibility of the proposed approach. The method allows for the observation of more prominent characteristics of meteoroid motion, providing a more detailed observation capability of velocity variations in other directions than previous methods.

Even a Blind Chicken Sometimes Finds a Grain of Corn—In My Case in Space

AbstractSometimes you need to take strategic risks even though you cannot know in advance where they will lead. I left my comfortable city life in Helsinki for a PhD position in space physics far away in the Arctic. The first part of the title of this paper is a compliment—originally a German proverb—a throwaway comment from a professor in connection with my decision. Good luck also helps. When I was appointed as a university lecturer, I did not have a clue about a new law in Sweden opening the possibility for promotion of suitably qualified lecturers to professorships. Taking risks have several times been to my advantage. Even my most important discovery, meteor head echoes, was the result of a risky idea for observing sporadic E‐layers. Instead, we got the first direct signals from the plasma coma around the very fast small grains entering from space into Earth's atmosphere monitored with a high‐power large‐aperture (HPLA) radar. In addition to my research activities, I have been interested in equal opportunities and gender issues. The many twists along my way have enriched my knowledge capital. At the top of my career, sitting in decision‐making bodies I finally learned and can now, afterward, reveal some secrets about how things work.

Лакунарный инсульт у мужчин молодого возраста

Background: ischemic strokes at a young age are one of the urgent problems of modern reality, since they occur in persons of working age. These vascular catastrophes are of great economic importance. Lacunar stroke (LS), or small vessel occlusion, is one of the main ischemic stroke (IS) subtypes with a variety of modifiable risk factors for its development. Aim: to evaluate the main risk factors, the stroke patterns and the endothelial function state in young male patients (18—50 y.o.) with LS. Patients and Methods: 46 male patients aged 18–50 y.o. with LS were included in the study. The NIHSS neurological deficit assessment scale, the Modified Rankin Scale and the Rivermead Mobility Index were used to objectify the severity of existing clinical symptoms and assess the IS severity. The patients underwent brain CT and/or MRI, ultrasound and duplex scanning of neck and head vessels, ECG, ECHO cardioscopy and laboratory examination. Shoulder ultrasound (SU) was used to assess the endothelial vasomotor function. Results: in the examined patients, the main risk factors were hypertension (97.8%), smoking (67.4%), dyslipidemia (41.3%) and obesity (8.7%). At the same time, the combination of hypertension and smoking was noted in 67.4% of cases, the combination of hypertension, smoking and regular alcohol consumption — in 17.4% of cases, atherosclerosis of the major arteries of the head — in 56.5% of cases. Isolated common carotid artery (CCA) stenosis was observed in 22.2% of cases, the degree of which varied from 20 to 35%, in 50% — internal carotid artery (ICA) stenosis (20—40%) and in 33.3% — combined stenoses of the CCA and ICA (25—60%). SU revealed a disorder in the form of a decreased vasomotor reactivity in 20 (58.8%) of the 34 examined patients. Conclusion: in male patients aged 18–50 y.o. with LS, multiple modifiable risk factors were identified. Ultrasound signs of endothelial dysfunction were detected in more than half of the patients. KEYWORDS: lacunar stroke, young age, modifiable risk factors, endothelial dysfunction, shoulder ultrasound. FOR CITATION: Pizov N.A., Baranova N.S., Pizova N.V., Bakucheva M.V. Lacunar stroke in young male patients. Russian Medical Inquiry. 2023;7(10):614–619 (in Russ.). DOI: 10.32364/2587-6821-2023-7-10-1.

Multi-instrument observations of the Pajala fireball: Origin, characteristics, and atmospheric implications

Meteor observations provide information about Solar System constituents and their influx onto Earth, their interaction processes in the atmosphere, as well as the neutral dynamics of the upper atmosphere. This study presents optical, radar, and infrasound measurements of a daytime fireball that occurred on 4 December 2020 at 13:30 UTC over Northeast Sweden. The fireball was recorded with two video cameras, allowing a trajectory determination to be made. The orbital parameters are compatible with the Northern Taurid meteor shower. The dynamic mass estimate based on the optical trajectory was found to be 0.6–1.7 kg, but this estimate can greatly vary from the true entry mass significantly due to the assumptions made. The meteor trail plasma was observed with an ionosonde as a sporadic E-like ionogram trace that lasted for 30 min. Infrasound emissions were detected at two sites, having propagation times consistent with a source location at an altitude of 80–90 km. Two VHF specular meteor radars observed a 6 minute long non-specular range spread trail echo as well as a faint head echo. Combined interferometric range-Doppler analysis of the meteor trail echoes at the two radars, allowed estimation of the mesospheric horizontal wind altitude profile, as well as tracking of the gradual deformation of the trail over time due to a prevailing neutral wind shear. This combined analysis indicates that the radar measurements of long-lived non-specular range-spread meteor trails produced by larger meteoroids can be used to measure the meteor radiant by observing the line traveled by the meteor. Furthermore, a multistatic meteor radar observation of these types of events can be used to estimate mesospheric neutral wind altitude profiles.

Meteor Head Echo Analyses From Concurrent Radar Observations at AMISR Resolute Bay, Jicamarca, and Millstone Hill

AbstractOn 10 and 11 October 2019, high‐power radar observations were performed simultaneously for 8 hours at Resolute Bay Incoherent Scatter North (RISR‐N), Jicamarca Radio Observatory (JRO), and Millstone Hill Observatory (MHO). The concurrent observations eliminate diurnal, seasonal, and space weather biases in the meteor head echo populations and elucidate relative sensitivities of each facility and configuration. Each facility observed thousands of head echoes, with JRO observing tens of thousands. An inter‐pulse phase matching technique employs Doppler shifts to determine head echo range rates (velocity component along radar beam) with order‐of‐magnitude greater accuracy versus measuring the Doppler shift at individual pulses, and this technique yields accurate range rates and decelerations for a subset of the head echo population at each facility. Because RISR‐N is at high latitude and points away from the ecliptic plane, it does not observe head echoes with range rates faster than 55 km/s, although its head echo population demonstrates a bias toward larger and faster head echoes. At JRO near the equator, a larger spread of range rates is observed. MHO observes a large spread of range rates at mid‐latitude despite its comparable frequency to RISR‐N, but this occurs because its beam was pointed at a 45° elevation angle unlike RISR‐N and JRO which were pointed near‐zenith. A trend of greater decelerations at lower altitudes is observed at RISR‐N and JRO, with decelerations of up to 60 km/s2, but high‐deceleration events of up to 1,000 km/s2 previously observed in head echo studies are not observed.

Meteor Detection With a New Computer Vision Approach

AbstractA novel computer vision‐based meteor head echo detection algorithm is developed to study meteor fluxes and their physical properties, including initial range, range coverage, and radial velocity. The proposed Algorithm for Head Echo Automatic Detection (AHEAD) comprises a feature extraction function and a Convolutional Neural Network (CNN). The former is tailored to identify meteor head echoes, and then a CNN is employed to remove false alarms. In the testing of meteor data collected with the Jicamarca 50 MHz incoherent scatter radar, the new algorithm detects over 180 meteors per minute at dawn, which is 2 to 10 times more sensitive than prior manual or algorithmic approaches, with a false alarm rate less than 1 percent. The present work lays the foundation of developing a fully automatic AI‐meteor package that detects, analyzes, and distinguishes among many types of meteor echoes. Furthermore, although initially evaluated for meteor data collected with the Jicamarca VHF incoherent radar, the new algorithm is generic enough that can be applied to other facilities with minor modifications. The CNN removes up to 98 percent of false alarms according to the testing set. We also present and discuss the physical characteristics of meteors detected with AHEAD, including flux rate, initial range, line of sight velocity, Signal‐to‐Noise Ratio, and noise characteristics. Our results indicate that stronger meteor echoes are detected at a slightly lower altitude and lower radial velocity than other meteors.

High-altitude meteors detected by the interferometric MU radar

ABSTRACTWe have re-analysed part of the middle and upper atmosphere (MU) radar meteor head echo data set collected during 2009–2010 and confirmed the existence of a rare high-altitude radar meteor population reaching up to ∼150 km altitude. The number of detections decreases significantly as a function of initial altitude. Out of the total amount of 106 000 events, 74 had an initial altitude >130 km while four of those had an initial altitude >145 km. High-altitude radar meteor observations have been reported before, e.g. using the EISCAT VHF radar and the Jicamarca Radio Observatory. The main novelty of this study is that the observations were performed using methods that render the final data set unambiguous in direction of arrival together with rigorously tested analysis routines that were validated by noisy raw data simulations. Due to our experimental set-up the maximum detectable range was limited to 148 km. Hence, we cannot confirm or deny the existence of radar meteors above that altitude.

Radar analysis algorithm for determining meteor head echo parameter probability distributions

ABSTRACT We present an automated radar data analysis algorithm developed to calculate probability distributions of meteor- and meteoroid parameters for head echoes detected with the Middle and Upper atmosphere (MU) radar in Shigaraki, Japan. The algorithm utilizes direct Monte Carlo simulations of uncertainties, with Bayesian Markov-chain Monte Carlo estimation of meteor model parameters and N-body propagation of distributions to perform orbit determination. The implementation has been validated using raw data simulations and a comparison with previous analysis methods. The concepts are applicable on a wide range of possible head echo measurements with other radar systems. The generated probability distributions provide quantitative reliability, which enables improved statistical studies and investigating the origins of detected meteoroids. The methodology section is highly detailed in order for the methods to be reproducible and provide a solid reference foundation for future studies. One such study is presented in a companion paper called ‘High-altitude meteors detected by the interferometric MU radar’.

Meteoroid orbit determination from HPLA radar data

High-power large-aperture radars have revolutionized meteor science by allowing highly accurate position and velocity estimates to be made from meteor head echoes. This paper describes a new open-source software, MODA, for determining the heliocentric orbital parameters of these meteoroids. We compare MODA with other current methods, both analytical and numerical. We describe our modeling of third-body perturbations and atmospheric drag, as well as solar radiation pressure, which is not taken into account in other works. We verify MODA against results from the literature and use it to compute the orbits for two small particles observed by ALTAIR in 2008.

Anewsimple method to observe Doppler shift of the meteor head echo using low-cost and low-power ham radio devices and free FFT software

Anewsimple method to observe Doppler shift of the meteor head echo using low-cost and low-power ham radio devices and free FFT software

Confirmation of Geminid meteor parameters via simultaneous 3-point radio observations of meteor head echoes using VHF ham radio waves and low-powered ham devices

Confirmation of Geminid meteor parameters via simultaneous 3-point radio observations of meteor head echoes using VHF ham radio waves and low-powered ham devices

Potential direct observation of meteoroid fragmentation by a high range resolution radar

In the development of Sanya Incoherent Scatter Radar (SYISR), which is a major scientific instrument project founded by the National Natural Science Foundation of China (NSFC), we established a prototype system of 8 subarrays (named SYISR-8 hereafter), including 256 transceiver modules totally, beginning in July 2018 to verify the functions of the radar. Based on SYISR-8, we configured the system to detect the meteor echo with high range resolution. During a continuous observation interval of 16 h, 55 meteor echo events were found. Among these events, 34 cases were head echoes, 18 cases were specular trail echoes, and 3 cases were head echo and nonspecular trail echo concurrent events. We have observed 2 potential direct meteoroid fragmentation cases of all 55 meteor events. It demonstrates that potential direct observation of meteoroid fragmentation could be observed by a relatively small aperture and power using pulse compression processing. However, the occurrence ratio of meteoroid fragmentation in our experiment is approximately 6%, which is considerably lower than that observed in previous studies, which needs further investigation.

An Improved Method to Measure Head Echoes Using a Meteor Radar

Abstract We present an improved methodology to obtain absolute position and velocity of meteor head echoes, which can yield orbital information, generally limited to the use of High-Power, Large-Aperture radars, using an advanced-designed specular meteor radar. The observations, which were performed during a period when an outburst of the β-Taurid meteor shower was expected, were performed with the Southern Argentine Agile MEteor Radar. Three different methodologies are utilized to confirm our results: an improved interferometric solver building on previous work, and two different target localization techniques using remote receiving stations. In addition, we performed simultaneous optical observations during the meteor shower period. Overall, 71 radar head echo events were detected and analyzed using interferometry, while 12 of those events have detected signals strong enough to be analyzed using localization methods at the remote sites. Due to poor weather, however, the optical cameras only observed two events simultaneously with the radar. Results from these events are in agreement with the radar results. We find that interferometry methods from both radar and optical data resulted in the most accurate estimation of meteor properties, while target localization techniques derived similar results, albeit with larger uncertainty. We also computed heliocentric meteoroid orbits, and while a fraction was hyperbolic, we believe these to be due to uncertainty. Two events are suspected to be β-Taurid shower members.

Effect of neutral winds on the creation of non-specular meteor trail echoes

Abstract. Non-specular meteor trail echoes are radar reflections from plasma instabilities that are caused by field-aligned irregularities. Meteor simulations are examined to show that these plasma instabilities, and thus the associated meteor trail echo, strongly depend on the meteoroid properties and the characteristics of the atmosphere in which the meteoroid is embedded. The effects of neutral winds, as a function of altitude, are analyzed to understand how their amplitude variability impacts the temporal–space signatures of non-specular meteor trail echoes present in very high-frequency (VHF) radar observations. It is found that amplitudes of the total horizontal neutral wind smaller than 0.6 m s−1 do not provide the right physical conditions to enable the genesis of non-specular meteor echoes. It is also found that a 0.0316 µg meteoroid traveling at 35 km s−1 can be seen as a meteor trail echo if the amplitudes of horizontal neutral winds are stronger than 15 m s−1. In contrast, a 0.316 µg meteoroid, traveling at the same speed, requires horizontal winds stronger than 1 m s−1 to be visible as a meteor trail echo. The neutral velocity threshold illustrates how simulations show that no trail echo is created below a critical wind value. This critical wind value is not mapped directly to radar observations, but it is used to shed light on the physics of meteor trails and improve their modeling. The meteor simulations also indicate that time delays on the order of hundreds of milliseconds or longer, between head echoes and non-specular echoes, which are present in VHF backscatter radar maps, can be a consequence of very dense plasma trails being affected by weak horizontal neutral winds that are smaller than 1 m s−1.

Simulation‐Derived Radar Cross Sections of a New Meteor Head Plasma Distribution Model

AbstractWe present results and analysis of finite‐difference time‐domain (FDTD) simulations of electromagnetic waves scattering off meteor head plasma using an analytical model and a simulation‐derived model of the head plasma distribution. The analytical model was developed by (Dimant & Oppenheim, 2017b, https://doi.org/10.1002/2017JA023963) and the simulation‐derived model is based on particle‐in‐cell (PIC) simulations presented in (Sugar et al., 2019, https://doi.org/10.1029/2018JA026434). Both of these head plasma distribution models show the meteor head plasma is significantly different than the spherically symmetric distributions used in previous studies of meteor head plasma. We use the FDTD simulation results to fit a power law model that relates the meteoroid ablation rate to the head echo radar cross section (RCS), and show that the RCS of plasma distributions derived from the Dimant‐Oppenheim analytical model and the PIC simulations agree to within 4 dBsm. The power law model yields more accurate meteoroid mass estimates than previous methods based on spherically symmetric plasma distributions.

Resolving the ambiguous direction of arrival of weak meteor radar trail echoes

Abstract. Meteor phenomena cause ionized plasmas that can be roughly divided into two distinctly different regimes: a dense and transient plasma region co-moving with the ablating meteoroid and a trail of diffusing plasma left in the atmosphere and moving with the neutral wind. Interferometric radar systems are used to observe the meteor trails and determine their positions and drift velocities. Depending on the spatial configuration of the receiving antennas and their individual gain patterns, the voltage response can be the same for several different plane wave directions of arrival (DOAs), thereby making it impossible to determine the correct direction. A low signal-to-noise ratio (SNR) can create the same effect probabilistically even if the system contains no theoretical ambiguities. Such is the case for the standard meteor trail echo data products of the Sodankylä Geophysical Observatory SKiYMET all-sky interferometric meteor radar. Meteor trails drift slowly enough in the atmosphere and allow for temporal integration, while meteor head echo targets move too fast. Temporal integration is a common method to increase the SNR of radar signals. For meteor head echoes, we instead propose to use direct Monte Carlo (DMC) simulations to validate DOA measurements. We have implemented two separate temporal integration methods and applied them to 2222 events measured by the Sodankylä meteor radar to simultaneously test the usefulness of such DMC simulations on cases where temporal integration is possible, validate the temporal integration methods, and resolve the ambiguous SKiYMET data products. The two methods are the temporal integration of the signal spatial correlations and matched-filter integration of the individual radar channel signals. The results are compared to Bayesian inference using the DMC simulations and the standard SkiYMET data products. In the examined data set, ∼ 13 % of the events were indicated as ambiguous. Out of these, ∼ 13 % contained anomalous signals. In ∼ 95 % of all ambiguous cases with a nominal signal, the three methods found one and the same output DOA, which was also listed as one of the ambiguous possibilities in the SkiYMET analysis. In all unambiguous cases, the results from all methods concurred.

Probabilistic analysis of ambiguities in radar echo direction of arrival from meteors

Abstract. Meteors and hard targets produce coherent radar echoes. If measured with an interferometric radar system, these echoes can be used to determine the position of the target through finding the direction of arrival (DOA) of the incoming echo onto the radar. Depending on the spatial configuration of radar-receiving antennas and their individual gain patterns, there may be an ambiguity problem when determining the DOA of an echo. Radars that are theoretically ambiguity-free are known to still have ambiguities that depend on the total radar signal-to-noise ratio (SNR). In this study, we investigate robust methods which are easy to implement to determine the effect of ambiguities on any hard target DOA determination by interferometric radar systems. We apply these methods specifically to simulate four different radar systems measuring meteor head and trail echoes, using the multiple signal classification (MUSIC) DOA determination algorithm. The four radar systems are the Middle And Upper Atmosphere (MU) radar in Japan, a generic Jones 2.5λ specular meteor trail radar configuration, the Middle Atmosphere Alomar Radar System (MAARSY) radar in Norway and the Program of the Antarctic Syowa Mesosphere Stratosphere Troposphere Incoherent Scatter (PANSY) radar in the Antarctic. We also examined a slightly perturbed Jones 2.5λ configuration used as a meteor trail echo receiver for the PANSY radar. All the results are derived from simulations, and their purpose is to grant understanding of the behaviour of DOA determination. General results are as follows: there may be a region of SNRs where ambiguities are relevant; Monte Carlo simulation determines this region and if it exists; the MUSIC function peak value is directly correlated with the ambiguous region; a Bayesian method is presented that may be able to analyse echoes from this region; the DOA of echoes with SNRs larger than this region are perfectly determined; the DOA of echoes with SNRs smaller than this region completely fail to be determined; the location of this region is shifted based on the total SNR versus the channel SNR in the direction of the target; and asymmetric subgroups can cause ambiguities, even for ambiguity-free radars. For a DOA located at the zenith, the end of the ambiguous region is located at 17 dB SNR for the MU radar and 3 dB SNR for the PANSY radar. The Jones radars are usually used to measure specular trail echoes far from zenith. The ambiguous region for a DOA at 75.5∘ elevation and 0∘ azimuth ends at 12 dB SNR. Using the Bayesian method, it may be possible to analyse echoes down to 4 dB SNR for the Jones configuration when given enough data points from the same target. The PANSY meteor trail echo receiver did not deviate significantly from the generic Jones configuration. The MAARSY radar could not resolve arbitrary DOAs sufficiently well enough to determine a stable region. However, if the DOA search is restricted to 70∘ elevation or above by assumption, stable DOA determination occurs above 15 dB SNR.

Dual frequency measurements of meteor head echoes simultaneously detected with the MAARSY and EISCAT radar systems

We present dual frequency measurements of common meteor head echoes, conducted with the VHF radar MAARSY (53.5 MHz) and the UHF EISCAT (930 MHz) radar located in Northern Norway. With temporal resolutions of 1ms, we find most head echoes show a continuous increase/decrease in radar cross section (RCS) with time at both frequencies. In some cases a sudden drop of several dBsm is detected by both radars, which we interpret as direct evidence for gross fragmentation. The mean difference of the RCS between both frequencies is about 17 dBsm at an average altitude of 100 km. We find a clear positive correlation between both RCS’s as well as a trend of RCS increasing with altitude, as expected (Close et al. 2002b). We were not able to find physically allowable fits to our dual frequency measurements for plasma radial distributions following either a 1r or 1r2 fall-off around the ablating meteoroid (Marshall et al. 2017). Assuming an overdense Gaussian plasma distribution, we estimated our typical meteoroid masses as ≈100 micrograms and a mean meteoroid density of ∼600kgm3. Two other plasma distribution functions (exponential and parabolic exponential) lead to slightly larger meteoroid densities of about ∼800kgm3. All of our meteor head echoes followed cometary-type orbits prior to Earth impact.

Meteor observations using radar imaging techniques and norm-constrained Capon method

Multifrequency and multireceiver techniques were employed simultaneously to examine the meteor echoes for the first time. A high-power-large-aperture radar−the Middle and Upper (MU) atmosphere radar (34.85oN, 136.10° E) was used in observation, with the radar beam directed to the geographic north and at 51° zenith. Receiving was done using 20 receivers and 5 carrier frequencies (46.250, 46.375, 46.500, 46.625, 46.750 ​MHz) for executing angular and range imaging of the meteor echoes, respectively. In addition to the conventional Capon and Fourier imaging methods, a norm-constrained Capon algorithm was also employed to improve the imaging results. Both meteor head echoes and long-duration range spread trail echoes (RSTEs, also known as non-specular meteor echoes) were observed simultaneously. It is demonstrated that range imaging is capable of resolving the evolution of RSTEs in the radar volume clearly, in which the branched RSTEs could be evidence of meteoroid fragmentation. On the other hand, angular imaging with single point of raw data (0.015s time resolution) can identify the multiple echo centers of meteor head echoes, which is also related to meteoroid fragmentation.

A Study on Meteor Head Echo Using a Probabilistic Detection Model at Jicamarca

AbstractA coded long pulse is applied to the Jicamarca 50 MHz high power large aperture radar to study meteor head echoes. We develop a probabilistic detection model, which finds 25% more meteors than the commonly used signal‐to‐noise threshold method. The long code and the probabilistic approach allow us to detect over 180 meteors per minute during the dawn hours, which is several times higher than reported previously. The typical mass of the meteoroids is estimated to be about 10−9 kg, slightly smaller than other sensitive very‐high‐frequency and ultrahigh‐frequency high power large aperture radars except the Arecibo radar. The high sensitivity allows us to observe numerous meteors in the presence of the strongest equatorial electrojet. We report and discuss the characteristics of meteor flux rate, ablation height, and velocity with a constant noise power for the first time for the Jicamarca radar. The highest average detection height is found to be near 2 a.m., instead of near 6 a.m. when the largest average velocity is observed. This is likely due to the combination of the relative large atmospheric velocity and the substantial atmospheric entry angles around 2 a.m. The observed characteristics suggest that many meteors are detected 8° off zenith despite that the full beam width is only 2.4°.