scholarly journals Planetary radar science case for EISCAT 3D

2021 ◽  
Vol 39 (3) ◽  
pp. 427-438
Author(s):  
Torbjørn Tveito ◽  
Juha Vierinen ◽  
Björn Gustavsson ◽  
Viswanathan Lakshmi Narayanan
Keyword(s):  
High Resolution ◽  
Radio Wave ◽  
Penetration Depth ◽  
Signal To Noise Ratio ◽  
Low Frequency ◽  
Physical Structure ◽  
The Moon ◽  
Signal To Noise ◽  
Resolution Mapping ◽  
Scattering Maps

Abstract. Ground-based inverse synthetic aperture radar is a tool that can provide insights into the early history and formative processes of planetary bodies in the inner solar system. This information is gathered by measuring the scattering matrix of the target body, providing composite information about the physical structure and chemical makeup of its surface and subsurface down to the penetration depth of the radio wave. This work describes the technical capabilities of the upcoming 233 MHz European Incoherent Scatter Scientific Association (EISCAT) 3D radar facility for measuring planetary surfaces. Estimates of the achievable signal-to-noise ratios for terrestrial target bodies are provided. While Venus and Mars can possibly be detected, only the Moon is found to have sufficient signal-to-noise ratio to allow high-resolution mapping to be performed. The performance of the EISCAT 3D antenna layout is evaluated for interferometric range–Doppler disambiguation, and it is found to be well suited for this task, providing up to 20 dB of separation between Doppler northern and southern hemispheres in our case study. The low frequency used by EISCAT 3D is more affected by the ionosphere than higher-frequency radars. The magnitude of the Doppler broadening due to ionospheric propagation effects associated with traveling ionospheric disturbances has been estimated. The effect is found to be significant but not severe enough to prevent high-resolution imaging. A survey of lunar observing opportunities between 2022 and 2040 is evaluated by investigating the path of the sub-radar point when the Moon is above the local radar horizon. During this time, a good variety of look directions and Doppler equator directions are found, with observations opportunities available for approximately 10 d every lunar month. EISCAT 3D will be able to provide new, high-quality polarimetric scattering maps of the nearside of the Moon with the previously unused wavelength of 1.3 m, which provides a good compromise between radio wave penetration depth and Doppler resolution.

scholarly journals Planetary Radar Science Case for EISCAT 3D

2020 ◽  
Author(s):  
Torbjørn Tveito ◽  
Juha Vierinen ◽  
Björn Gustavsson ◽  
Viswanathan Lakshmi Narayanan
Keyword(s):  
High Resolution ◽  
Radio Wave ◽  
Penetration Depth ◽  
Signal To Noise Ratio ◽  
Low Frequency ◽  
Physical Structure ◽  
The Moon ◽  
Signal To Noise ◽  
Resolution Mapping ◽  
Resolution Imaging

Abstract. Ground-based inverse synthetic aperture radar is a tool that can provide insights into the early history and formative processes of planetary bodies in the inner Solar System. This information is gathered by measuring the scattering matrix of the target body, providing composite information about the physical structure and chemical makeup of its surface and subsurface down to the penetration depth of the radio wave. This work describes the technical capabilities of the upcoming 233 MHz EISCAT 3D radar facility for measuring planetary surfaces. Estimates of the achievable signal-to-noise ratios for terrestrial target bodies are provided. While Venus and Mars can possibly be detected, only the Moon is found to have sufficient signal-to-noise ratio to allow high resolution mapping to be performed. The performance of the EISCAT 3D antenna layout is evaluated for interferometric range-Doppler disambiguation and it is found to be well suited for this task, providing up to 20 dB of separation between Doppler north and south hemispheres in our case study. The low frequency used by EISCAT 3D is more affected by the ionosphere than higher frequency radars. The magnitude of the Doppler broadening due to ionospheric propagation effects associated with traveling ionospheric disturbances has been estimated.The effect is found to be significant, but not severe enough to prevent high resolution imaging. A survey of Lunar observing opportunities between 2022 and 2040 are evaluated by investigating the path of the sub-radar point when the Moon is above the local radar horizon. During this time, a good variety of look directions and Doppler equator directions are found, with observations opportunities available for approximately ten days every lunar month. EISCAT 3D will be able to provide new high quality polarimetric scattering map of the near-side of the Moon with a previously unused wavelength of 1.3 m, which provides a good compromise between radio wave penetration depth and Doppler resolution.

Denoising for full-waveform inversion with expanded prediction-error filters

Geophysics ◽  
2021 ◽  
pp. 1-54
Author(s):  
Milad Bader ◽  
Robert G. Clapp ◽  
Biondo Biondi
Keyword(s):  
High Frequency ◽  
Prediction Error ◽  
Signal To Noise Ratio ◽  
Waveform Inversion ◽  
Low Frequency ◽  
Full Waveform Inversion ◽  
Frequency Data ◽  
Signal To Noise ◽  
Frequency Signal ◽  
Full Waveform

Low-frequency data below 5 Hz are essential to the convergence of full-waveform inversion towards a useful solution. They help build the velocity model low wavenumbers and reduce the risk of cycle-skipping. In marine environments, low-frequency data are characterized by a low signal-to-noise ratio and can lead to erroneous models when inverted, especially if the noise contains coherent components. Often field data are high-pass filtered before any processing step, sacrificing weak but essential signal for full-waveform inversion. We propose to denoise the low-frequency data using prediction-error filters that we estimate from a high-frequency component with a high signal-to-noise ratio. The constructed filter captures the multi-dimensional spectrum of the high-frequency signal. We expand the filter's axes in the time-space domain to compress its spectrum towards the low frequencies and wavenumbers. The expanded filter becomes a predictor of the target low-frequency signal, and we incorporate it in a minimization scheme to attenuate noise. To account for data non-stationarity while retaining the simplicity of stationary filters, we divide the data into non-overlapping patches and linearly interpolate stationary filters at each data sample. We apply our method to synthetic stationary and non-stationary data, and we show it improves the full-waveform inversion results initialized at 2.5 Hz using the Marmousi model. We also demonstrate that the denoising attenuates non-stationary shear energy recorded by the vertical component of ocean-bottom nodes.

scholarly journals Signal-to-noise ratio in the membrane potential of the owl's auditory coincidence detectors

2012 ◽  
Vol 108 (10) ◽  
pp. 2837-2845 ◽  
Author(s):  
Go Ashida ◽  
Kazuo Funabiki ◽  
Paula T. Kuokkanen ◽  
Richard Kempter ◽  
Catherine E. Carr
Keyword(s):  
Neural Circuit ◽  
Signal To Noise Ratio ◽  
Phase Locking ◽  
Low Frequency ◽  
Membrane Potentials ◽  
Signal To Noise ◽  
Theoretical Predictions ◽  
Noise Ratio ◽  
Band Limited

Owls use interaural time differences (ITDs) to locate a sound source. They compute ITD in a specialized neural circuit that consists of axonal delay lines from the cochlear nucleus magnocellularis (NM) and coincidence detectors in the nucleus laminaris (NL). Recent physiological recordings have shown that tonal stimuli induce oscillatory membrane potentials in NL neurons (Funabiki K, Ashida G, Konishi M. J Neurosci 31: 15245–15256, 2011). The amplitude of these oscillations varies with ITD and is strongly correlated to the firing rate. The oscillation, termed the sound analog potential, has the same frequency as the stimulus tone and is presumed to originate from phase-locked synaptic inputs from NM fibers. To investigate how these oscillatory membrane potentials are generated, we applied recently developed signal-to-noise ratio (SNR) analysis techniques (Kuokkanen PT, Wagner H, Ashida G, Carr CE, Kempter R. J Neurophysiol 104: 2274–2290, 2010) to the intracellular waveforms obtained in vivo. Our theoretical prediction of the band-limited SNRs agreed with experimental data for mid- to high-frequency (>2 kHz) NL neurons. For low-frequency (≤2 kHz) NL neurons, however, measured SNRs were lower than theoretical predictions. These results suggest that the number of independent NM fibers converging onto each NL neuron and/or the population-averaged degree of phase-locking of the NM fibers could be significantly smaller in the low-frequency NL region than estimated for higher best-frequency NL.

scholarly journals On cross-correlations, averages and noise in electron microscopy

2019 ◽  
Vol 75 (1) ◽  
pp. 12-18 ◽  
Author(s):  
Michael Radermacher ◽  
Teresa Ruiz
Keyword(s):  
High Resolution ◽  
Cross Correlation ◽  
Signal To Noise Ratio ◽  
3D Structure ◽  
Signal To Noise ◽  
High Resolution Structure ◽  
Multiple Copies ◽  
High Level ◽  
2D Images ◽  
Resolution Structure

Biological samples are radiation-sensitive and require imaging under low-dose conditions to minimize damage. As a result, images contain a high level of noise and exhibit signal-to-noise ratios that are typically significantly smaller than 1. Averaging techniques, either implicit or explicit, are used to overcome the limitations imposed by the high level of noise. Averaging of 2D images showing the same molecule in the same orientation results in highly significant projections. A high-resolution structure can be obtained by combining the information from many single-particle images to determine a 3D structure. Similarly, averaging of multiple copies of macromolecular assembly subvolumes extracted from tomographic reconstructions can lead to a virtually noise-free high-resolution structure. Cross-correlation methods are often used in the alignment and classification steps of averaging processes for both 2D images and 3D volumes. However, the high noise level can bias alignment and certain classification results. While other approaches may be implicitly affected, sensitivity to noise is most apparent in multireference alignments, 3D reference-based projection alignments and projection-based volume alignments. Here, the influence of the image signal-to-noise ratio on the value of the cross-correlation coefficient is analyzed and a method for compensating for this effect is provided.

scholarly journals Differential Recordings of Local Field Potential:A Genuine Tool to Quantify Functional Connectivity

2018 ◽  
Author(s):  
Meyer Gabriel ◽  
Caponcy Julien ◽  
Paul A. Salin ◽  
Comte Jean-Christophe
Keyword(s):  
Functional Connectivity ◽  
Local Field ◽  
Signal To Noise Ratio ◽  
Field Potential ◽  
Low Frequency ◽  
Large Area ◽  
Signal To Noise ◽  
Cortical Areas ◽  
Electrophysiological Method ◽  
Local Field Potential Lfp

AbstractLocal field potential (LFP) recording is a very useful electrophysiological method to study brain processes. However, this method is criticized for recording low frequency activity in a large area of extracellular space potentially contaminated by distal activity. Here, we theoretically and experimentally compare ground-referenced (RR) with differential recordings (DR). We analyze electrical activity in the rat cortex with these two methods. Compared with RR, DR reveals the importance of local phasic oscillatory activities and their coherence between cortical areas. Finally, we show that DR provides a more faithful assessment of functional connectivity caused by an increase in the signal to noise ratio, and of the delay in the propagation of information between two cortical structures.

DCT Image Steganography Analysis for Privacy Preserving Data Mining

2016 ◽  
Vol 7 (3) ◽  
pp. 1-9 ◽  
Author(s):  
Sahar A. El-Rahman Ismail ◽  
Dalal Al Makhdhub ◽  
Amal A. Al Qahtani ◽  
Ghadah A. Al Shabanat ◽  
Nouf M. Omair ◽  
...  
Keyword(s):  
Data Mining ◽  
Information Hiding ◽  
Signal To Noise Ratio ◽  
Low Frequency ◽  
Privacy Preserving ◽  
Sensitive Information ◽  
Signal To Noise ◽  
Privacy Preserving Data Mining ◽  
Frequency Domains ◽  
Privacy And Confidentiality

We live in an information era where sensitive information extracted from data mining systems is vulnerable to exploitation. Privacy preserving data mining aims to prevent the discovery of sensitive information. Information hiding systems provide excellent privacy and confidentiality, where securing confidential communications in public channels can be achieved using steganography. A cover media are exploited using steganography techniques where they hide the payload's existence within appropriate multimedia carriers. This paper aims to study steganography techniques in spatial and frequency domains, and then analyzes the performance of Discrete Cosine Transform (DCT) based steganography using the low frequency and the middle frequency to compare their performance using Peak Signal to Noise Ratio (PSNR) and Mean Square Error (MSE). The experimental results show that middle frequency has the larger message capacity and best performance.

Development of a Philips cryo-TEM provided with a liquid helium cooled tilt stage and a vacuum transfer system

1998 ◽  
Vol 4 (S2) ◽  
pp. 400-401
Author(s):  
R. Wagner ◽  
A.F. de Jong ◽  
A.G. Koster ◽  
R. Morrison ◽  
F. Tothill ◽  
...  
Keyword(s):  
High Resolution ◽  
Liquid Helium ◽  
Signal To Noise Ratio ◽  
Transfer System ◽  
Helium Temperature ◽  
Single Particles ◽  
Signal To Noise ◽  
Specimen Holder ◽  
2D Crystals ◽  
Beam Damage

In order to reduce beam damage, biological TEM specimens are often observed at temperatures close to the boiling point of liquid nitrogen (77 K). Recently, encouraging results on single particles as well as on 2D crystals have appeared, derived from images taken near liquid helium temperature (4 K), in dedicated TEMs. At these temperatures the high resolution frequencies are much better preserved, increasing the allowable dose and thus the signal to noise ratio.4 Here we present the design of a new dedicated Philips He-TEM which combines the full functionality of a CM300 TWIN with a vacuum transfer system and a liquid helium cooled specimen holder.A schematic overview of the Cryo-TEM is shown in figure 1. The key differences compared to a standard CM microscope are: 1) The tip of the specimen rod is cooled below 10 K and the rod itself cannot be taken out of the goniometer (CompuStage). 2) The specimen enters the column on the opposite side.

scholarly journals Detection of Small Magnetic Fields Using Serial Magnetic Tunnel Junctions with Various Geometrical Characteristics

Sensors ◽  
2020 ◽  
Vol 20 (19) ◽  
pp. 5704
Author(s):  
Zhenhu Jin ◽  
Yupeng Wang ◽  
Kosuke Fujiwara ◽  
Mikihiko Oogane ◽  
Yasuo Ando
Keyword(s):  
Magnetic Fields ◽  
Signal To Noise Ratio ◽  
Low Frequency ◽  
High Signal ◽  
Free Layer ◽  
Signal To Noise ◽  
Noise Spectral Density ◽  
Junction Area ◽  
Geometrical Characteristics ◽  
Noise Ratio

Thanks to their high magnetoresistance and integration capability, magnetic tunnel junction-based magnetoresistive sensors are widely utilized to detect weak, low-frequency magnetic fields in a variety of applications. The low detectivity of MTJs is necessary to obtain a high signal-to-noise ratio when detecting small variations in magnetic fields. We fabricated serial MTJ-based sensors with various junction area and free-layer electrode aspect ratios. Our investigation showed that their sensitivity and noise power are affected by the MTJ geometry due to the variation in the magnetic shape anisotropy. Their MR curves demonstrated a decrease in sensitivity with an increase in the aspect ratio of the free-layer electrode, and their noise properties showed that MTJs with larger junction areas exhibit lower noise spectral density in the low-frequency region. All of the sensors were able detect a small AC magnetic field (Hrms = 0.3 Oe at 23 Hz). Among the MTJ sensors we examined, the sensor with a square-free layer and large junction area exhibited a high signal-to-noise ratio (4792 ± 646). These results suggest that MTJ geometrical characteristics play a critical role in enhancing the detectivity of MTJ-based sensors.

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