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.

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Resolving ambiguous direction of arrival of weak meteor radar trail echoes

10.5194/amt-2020-220 ◽

2020 ◽

Author(s):

Daniel Kastinen ◽

Johan Kero ◽

Alexander Kozlovsky ◽

Mark Lester

Keyword(s):

Spatial Correlation ◽

Spatial Configuration ◽

Measurement Data ◽

Radar Data ◽

Voltage Response ◽

Meteor Radar ◽

Data Set ◽

Coherent Integration ◽

Meteor Trails ◽

The One

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A search for transiting planets in the β Pictoris system

Astronomy and Astrophysics ◽

10.1051/0004-6361/201731941 ◽

2018 ◽

Vol 615 ◽

pp. A145 ◽

Cited By ~ 3

Author(s):

M. Mol Lous ◽

E. Weenk ◽

M. A. Kenworthy ◽

K. Zwintz ◽

R. Kuschnig

Keyword(s):

Signal To Noise Ratio ◽

Large Fraction ◽

Young Star ◽

High Signal ◽

Data Set ◽

Transiting Planets ◽

Using Data ◽

Exoplanet Systems ◽

Transit Signals

Context. Transiting exoplanets provide an opportunity for the characterization of their atmospheres, and finding the brightest star in the sky with a transiting planet enables high signal-to-noise ratio observations. The Kepler satellite has detected over 365 multiple transiting exoplanet systems, a large fraction of which have nearly coplanar orbits. If one planet is seen to transit the star, then it is likely that other planets in the system will transit the star too. The bright (V = 3.86) star β Pictoris is a nearby young star with a debris disk and gas giant exoplanet, β Pictoris b, in a multi-decade orbit around it. Both the planet’s orbit and disk are almost edge-on to our line of sight. Aims. We carry out a search for any transiting planets in the β Pictoris system with orbits of less than 30 days that are coplanar with the planet β Pictoris b. Methods. We search for a planetary transit using data from the BRITE-Constellation nanosatellite BRITE-Heweliusz, analyzing the photometry using the Box-Fitting Least Squares Algorithm (BLS). The sensitivity of the method is verified by injection of artificial planetary transit signals using the Bad-Ass Transit Model cAlculatioN (BATMAN) code. Results. No planet was found in the BRITE-Constellation data set. We rule out planets larger than 0.6 RJ for periods of less than 5 days, larger than 0.75 RJ for periods of less than 10 days, and larger than 1.05 RJ for periods of less than 20 days.

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Code Optimisation Framework for Multicode Sonar Systems

10.26686/wgtn.17143973.v1 ◽

2021 ◽

Author(s):

◽

Muhammad Rashed

Keyword(s):

Transmission Loss ◽

Matched Filter ◽

Signal To Noise Ratio ◽

Welch Bound ◽

Optimisation Algorithm ◽

Sonar System ◽

Channel Effects ◽

Sonar Systems ◽

Mismatched Filters ◽

Quadratically Constrained

<p>The ocean is a temporally and spatially varying environment, the characteristics of which pose significant challenges to the development of effective underwater wireless communications and sensing systems. An underwater sensing system such as a sonar detects the presence of a known signal through correlation. It is advantageous to use multiple transducers to increase surveying area with reduced surveying costs and time. Each transducers is assigned a dedicated code. When using multiple codes, the sidelobes of auto- and crosscorrelations are restricted to theoretical limits known as bounds. Sets of codes must be optimised in order to achieve optimal correlation properties, and, achieve Sidelobe Level (SLL)s as low as possible. In this thesis, we present a novel code-optimisation method to optimise code-sets with any number of codes and up to any length of each code. We optimise code-sets for a matched filter for application in a multi-code sonar system. We first present our gradient-descent based algorithm to optimise sets of codes for flat and low crosscorrelations and autocorrelation sidelobes, including conformance of the magnitude of the samples of the codes to a target power profile. We incorporate the transducer frequency response and the channel effects into the optimisation algorithm. We compare the correlations of our optimised codes with the well-known Welch bound. We then present a method to widen the autocorrelation mainlobe and impose monotonicity. In many cases, we are able to achieve SLLs beyond the Welch bound. We study the Signal to Noise Ratio (SNR) improvement of the optimised codes for an Underwater Acoustic (UWA) channel. During its propagation, the acoustic wave suffers non-constant transmission loss which is compensated by the application of an appropriate Time Variable Gain (TVG). The effect of the TVG modifies the noise received with the signal. We show that in most cases, the matched filter is still the optimum filter. We also show that the accuracy in timing is very important in the application of the TVG to the received signal. We then incorporate Doppler tolerance into the existing optimisation algorithm. Our proposed method is able to optimise sets of codes for multiple Doppler scaling factors and non-integer delays in the arrival of the reflection, while still conforming to other constraints. We suggest designing mismatched filters to further reduce the SLLs, firstly using an existing Quadratically Constrained Qaudratic Program (QCQP) formulation and secondly, as a local optimisation problem, modifying our basic optimisation algorithm.</p>

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Variations in noise and signal levels in a pair of deep boreholes near Amarillo, Texas

Bulletin of the Seismological Society of America ◽

10.1785/bssa0840051593 ◽

1994 ◽

Vol 84 (5) ◽

pp. 1593-1607

Author(s):

Christopher J. Young ◽

Eric P. Chael ◽

David A. Zagar ◽

Jerry A. Carter

Keyword(s):

Noise Level ◽

Signal To Noise Ratio ◽

Body Wave ◽

Working Hours ◽

Data Set ◽

Frequency Independent ◽

Deep Boreholes ◽

Strong Body ◽

Borehole Seismic ◽

40 Hz

Abstract To better understand the depth dependence of improvements in signal-to-noise ratio for borehole seismic data, we have collected and analyzed a data set recorded from a pair of high-fidelity, broadband (1 to 80 Hz) seismometers sited in two closely separated deep boreholes near Amarillo, Texas. The total decrease (surface to 1951 m) in minimum noise level is up to 30 dB; the total decrease in maximum noise level is up to 35 dB; and the range of noise values (maximum to minimum) at a given depth decreases from 30 to 10 dB. The majority of the noise reduction occurs within the first few hundred meters below the surface, but the decrease continues with depth and there is no indication that even lower noise levels do not exist below our deepest recording depth (1951 m). Cultural work-day noise (prominent during normal working hours) from 0 to 40 Hz is observed at all depths, suggesting a strong body-wave component. Wind-generated 15 to 60-Hz noise is strongest at the surface, and is observed as deep as 367 m without a properly shielded hole. With the addition of shielding to reduce the coupling between the borehole casing and/or cable with the wind, wind-generated noise above 40 Hz can be eliminated at 367 m. Events with near-vertical propagation paths and signal power above 1 Hz show signal strength decreasing uphole, with a steady winnowing of high frequencies that can be fit by a simple frequency-independent Q of 35.5 ± 8 for the material between 1951 and 367 m.

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Refraction wavefield migration

Geophysics ◽

10.1190/geo2020-0141.1 ◽

2020 ◽

Vol 85 (6) ◽

pp. Q27-Q37

Author(s):

Yang Shen ◽

Jie Zhang

Keyword(s):

Signal To Noise Ratio ◽

Surface Velocity ◽

Data Set ◽

Near Surface ◽

Depth Migration ◽

Reflection Data ◽

Imaging Tool ◽

Imaging Results ◽

Migration Method ◽

Single Method

Refraction methods are often applied to model and image near-surface velocity structures. However, near-surface imaging is very challenging, and no single method can resolve all of the land seismic problems across the world. In addition, deep interfaces are difficult to image from land reflection data due to the associated low signal-to-noise ratio. Following previous research, we have developed a refraction wavefield migration method for imaging shallow and deep interfaces via interferometry. Our method includes two steps: converting refractions into virtual reflection gathers and then applying a prestack depth migration method to produce interface images from the virtual reflection gathers. With a regular recording offset of approximately 3 km, this approach produces an image of a shallow interface within the top 1 km. If the recording offset is very long, the refractions may follow a deep path, and the result may reveal a deep interface. We determine several factors that affect the imaging results using synthetics. We also apply the novel method to one data set with regular recording offsets and another with far offsets; both cases produce sharp images, which are further verified by conventional reflection imaging. This method can be applied as a promising imaging tool when handling practical cases involving data with excessively weak or missing reflections but available refractions.

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Public HARPS radial velocity database corrected for systematic errors

Astronomy and Astrophysics ◽

10.1051/0004-6361/201936686 ◽

2020 ◽

Vol 636 ◽

pp. A74 ◽

Cited By ~ 16

Author(s):

Trifon Trifonov ◽

Lev Tal-Or ◽

Mathias Zechmeister ◽

Adrian Kaminski ◽

Shay Zucker ◽

...

Keyword(s):

Radial Velocity ◽

Signal To Noise Ratio ◽

Auxiliary Information ◽

Easy Access ◽

High Signal ◽

M Dwarfs ◽

Data Set ◽

New Public ◽

Systematic Effects ◽

User Friendly

Context. The High Accuracy Radial velocity Planet Searcher (HARPS) spectrograph has been mounted since 2003 at the ESO 3.6 m telescope in La Silla and provides state-of-the-art stellar radial velocity (RV) measurements with a precision down to ∼1 m s−1. The spectra are extracted with a dedicated data-reduction software (DRS), and the RVs are computed by cross-correlating with a numerical mask. Aims. This study has three main aims: (i) Create easy access to the public HARPS RV data set. (ii) Apply the new public SpEctrum Radial Velocity AnaLyser (SERVAL) pipeline to the spectra, and produce a more precise RV data set. (iii) Determine whether the precision of the RVs can be further improved by correcting for small nightly systematic effects. Methods. For each star observed with HARPS, we downloaded the publicly available spectra from the ESO archive and recomputed the RVs with SERVAL. This was based on fitting each observed spectrum with a high signal-to-noise ratio template created by coadding all the available spectra of that star. We then computed nightly zero-points (NZPs) by averaging the RVs of quiet stars. Results. By analyzing the RVs of the most RV-quiet stars, whose RV scatter is < 5 m s−1, we find that SERVAL RVs are on average more precise than DRS RVs by a few percent. By investigating the NZP time series, we find three significant systematic effects whose magnitude is independent of the software that is used to derive the RV: (i) stochastic variations with a magnitude of ∼1 m s−1; (ii) long-term variations, with a magnitude of ∼1 m s−1 and a typical timescale of a few weeks; and (iii) 20–30 NZPs that significantly deviate by a few m s−1. In addition, we find small (≲1 m s−1) but significant intra-night drifts in DRS RVs before the 2015 intervention, and in SERVAL RVs after it. We confirm that the fibre exchange in 2015 caused a discontinuous RV jump that strongly depends on the spectral type of the observed star: from ∼14 m s−1 for late F-type stars to ∼ − 3 m s−1 for M dwarfs. The combined effect of extracting the RVs with SERVAL and correcting them for the systematics we find is an improved average RV precision: an improvement of ∼5% for spectra taken before the 2015 intervention, and an improvement of ∼15% for spectra taken after it. To demonstrate the quality of the new RV data set, we present an updated orbital solution of the GJ 253 two-planet system. Conclusions. Our NZP-corrected SERVAL RVs can be retrieved from a user-friendly public database. It provides more than 212 000 RVs for about 3000 stars along with much auxiliary information, such as the NZP corrections, various activity indices, and DRS-CCF products.

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Coded continuous wave meteor radar

Atmospheric Measurement Techniques ◽

10.5194/amt-9-829-2016 ◽

2016 ◽

Vol 9 (2) ◽

pp. 829-839 ◽

Cited By ~ 9

Author(s):

Juha Vierinen ◽

Jorge L. Chau ◽

Nico Pfeffer ◽

Matthias Clahsen ◽

Gunter Stober

Keyword(s):

Frequency Band ◽

Peak Power ◽

Large Scale ◽

Pulse Compression ◽

Continuous Wave ◽

Signal To Noise Ratio ◽

Radar Data ◽

Meteor Radar ◽

To Receive ◽

Computation Speed

Abstract. The concept of a coded continuous wave specular meteor radar (SMR) is described. The radar uses a continuously transmitted pseudorandom phase-modulated waveform, which has several advantages compared to conventional pulsed SMRs. The coding avoids range and Doppler aliasing, which are in some cases problematic with pulsed radars. Continuous transmissions maximize pulse compression gain, allowing operation at lower peak power than a pulsed system. With continuous coding, the temporal and spectral resolution are not dependent on the transmit waveform and they can be fairly flexibly changed after performing a measurement. The low signal-to-noise ratio before pulse compression, combined with independent pseudorandom transmit waveforms, allows multiple geographically separated transmitters to be used in the same frequency band simultaneously without significantly interfering with each other. Because the same frequency band can be used by multiple transmitters, the same interferometric receiver antennas can be used to receive multiple transmitters at the same time. The principles of the signal processing are discussed, in addition to discussion of several practical ways to increase computation speed, and how to optimally detect meteor echoes. Measurements from a campaign performed with a coded continuous wave SMR are shown and compared with two standard pulsed SMR measurements. The type of meteor radar described in this paper would be suited for use in a large-scale multi-static network of meteor radar transmitters and receivers. Such a system would be useful for increasing the number of meteor detections to obtain improved meteor radar data products.

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Signal coding in cockroach photoreceptors is tuned to dim environments

Journal of Neurophysiology ◽

10.1152/jn.00588.2012 ◽

2012 ◽

Vol 108 (10) ◽

pp. 2641-2652 ◽

Cited By ~ 24

Author(s):

K. Heimonen ◽

E.-V. Immonen ◽

R. V. Frolov ◽

I. Salmela ◽

M. Juusola ◽

...

Keyword(s):

Information Transfer ◽

Periplaneta Americana ◽

Single Photon ◽

Signal To Noise Ratio ◽

Temporal Integration ◽

High Sensitivity ◽

Single Photons ◽

Low Frequencies ◽

Whole Cell Patch Clamp ◽

High Level

In dim light, scarcity of photons typically leads to poor vision. Nonetheless, many animals show visually guided behavior with dim environments. We investigated the signaling properties of photoreceptors of the dark active cockroach ( Periplaneta americana) using intracellular and whole-cell patch-clamp recordings to determine whether they show selective functional adaptations to dark. Expectedly, dark-adapted photoreceptors generated large and slow responses to single photons. However, when light adapted, responses of both phototransduction and the nontransductive membrane to white noise (WN)-modulated stimuli remained slow with corner frequencies ∼20 Hz. This promotes temporal integration of light inputs and maintains high sensitivity of vision. Adaptive changes in dynamics were limited to dim conditions. Characteristically, both step and frequency responses stayed effectively unchanged for intensities >1,000 photons/s/photoreceptor. A signal-to-noise ratio (SNR) of the light responses was transiently higher at frequencies <5 Hz for ∼5 s after light onset but deteriorated to a lower value upon longer stimulation. Naturalistic light stimuli, as opposed to WN, evoked markedly larger responses with higher SNRs at low frequencies. This allowed realistic estimates of information transfer rates, which saturated at ∼100 bits/s at low-light intensities. We found, therefore, selective adaptations beneficial for vision in dim environments in cockroach photoreceptors: large amplitude of single-photon responses, constant high level of temporal integration of light inputs, saturation of response properties at low intensities, and only transiently efficient encoding of light contrasts. The results also suggest that the sources of the large functional variability among different photoreceptors reside mostly in phototransduction processes and not in the properties of the nontransductive membrane.

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Sparse spectral attributes to detect hydrocarbons: A case study from deep dolomite reservoirs

Interpretation ◽

10.1190/int-2018-0170.1 ◽

2019 ◽

Vol 7 (3) ◽

pp. T701-T711

Author(s):

Jianhu Gao ◽

Bingyang Liu ◽

Shengjun Li ◽

Hongqiu Wang

Keyword(s):

Seismic Data ◽

Signal To Noise Ratio ◽

Low Frequency ◽

Spectral Amplitude ◽

Data Set ◽

Frequency Spectra ◽

Hydrocarbon Production ◽

Hydrocarbon Detection ◽

Time Frequency ◽

Gas Bearing

Hydrocarbon detection is always one of the most critical sections in geophysical exploration, which plays an important role in subsequent hydrocarbon production. However, due to the low signal-to-noise ratio and weak reflection amplitude of deep seismic data, some conventional methods do not always provide favorable hydrocarbon prediction results. The interesting dolomite reservoirs in Central Sichuan are buried over an average depth of 4500 m, and the dolomite rocks have a low porosity below approximately 4%, which is measured by well-logging data. Furthermore, the dominant system of pores and fractures as well as strong heterogeneity along the lateral and vertical directions lead to some difficulties in describing the reservoir distribution. Spectral decomposition (SD) has become successful in illuminating subsurface features and can also be used to identify potential hydrocarbon reservoirs by detecting low-frequency shadows. However, the current applications for hydrocarbon detection always suffer from low resolution for thin reservoirs, probably due to the influence of the window function and without a prior constraint. To address this issue, we developed sparse inverse SD (SISD) based on the wavelet transform, which involves a sparse constraint of time-frequency spectra. We focus on investigating the applications of sparse spectral attributes derived from SISD to deep marine dolomite hydrocarbon detection from a 3D real seismic data set with an area of approximately [Formula: see text]. We predict and evaluate gas-bearing zones in two target reservoir segments by analyzing and comparing the spectral amplitude responses of relatively high- and low-frequency components. The predicted results indicate that most favorable gas-bearing areas are located near the northeast fault zone in the upper reservoir segment and at the relatively high structural positions in the lower reservoir segment, which are in good agreement with the gas-testing results of three wells in the study area.

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On a certain class of one step temporal integration methods for standard dissipative continua

Computational Mechanics ◽

10.1007/s00466-020-01931-0 ◽

2020 ◽

Author(s):

Sebastian Stark

Keyword(s):

Temporal Integration ◽

Integration Methods ◽

One Step

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