scholarly journals Revision of the Atmospheric Modeling for SNR Observations in Ground-Based GNSS Reflectometry

2021 ◽  
Author(s):  
Jörg Reinking
Keyword(s):  
Signal To Noise Ratio ◽  
Propagation Delay ◽  
Atmospheric Modeling ◽  
Delay Model ◽  
Atmospheric Refraction ◽  
Spherical Reflector ◽  
Coastal Sea ◽  
Gnss Reflectometry ◽  
Ray Bending ◽  
Operational Tool

The application of signal-to-noise ratio (SNR) observations from ground-based GNSS Reflectometry is becoming an operational tool for coastal sea-level altimetry. As in all data analyses, systematic influences must be reduced here too, to achieve reliable results. A prominent influence results from atmospheric refraction. Different approaches exist to describe or to correct for this influence. In our contribution we will revise the latest developments and suggest a simple atmospheric interferometric delay model that takes into account ray bending as well as along-path propagation delay. The model takes into account a spherical reflector and can therefore be applied for data from very low elevation angles, too. The findings are double-checked by numerical experiments based on a step-by-step raytracing procedure.

scholarly journals Revision of the Atmospheric Modeling for SNR Observations in Ground-Based GNSS Reflectometry

2020 ◽  
Author(s):  
Jörg Reinking
Keyword(s):  
Numerical Experiments ◽  
Propagation Delay ◽  
Atmospheric Modeling ◽  
Delay Model ◽  
Atmospheric Refraction ◽  
Data Analyses ◽  
Coastal Sea ◽  
Gnss Reflectometry ◽  
Ray Bending ◽  
Operational Tool

The application of signal-to-noise (SNR) observations from ground-based GNSS Reflectometry is becoming an operational tool for coastal sea-level altimetry. As in all data analyses, systematic influences must be reduced here too, to achieve reliable results. A prominent influence results from atmospheric refraction. Different approaches exist to describe or to correct for this influence. In our contribution we will revise the latest developments and suggest a simple atmospheric interferometric delay model that takes into account ray bending as well as along-path propagation delay. The findings are double-checked by numerical experiments based on a step-by-step raytracing procedure.

scholarly journals Assessment of Effective Network Connectivity among MEG None Contaminated Epileptic Transitory Events

2021 ◽  
Vol 2021 ◽  
pp. 1-14
Author(s):  
Abir Hadriche ◽  
Ichrak Behy ◽  
Amal Necibi ◽  
Abdennaceur Kachouri ◽  
Chokri Ben Amar ◽  
...  
Keyword(s):  
Inverse Problem ◽  
Clinical Performance ◽  
Signal To Noise Ratio ◽  
Statistical Parametric Mapping ◽  
Simulated Data ◽  
Network Connectivity ◽  
Propagation Delay ◽  
Connection Strength ◽  
Advanced Technique ◽  
Epileptiform Discharges

Characterizing epileptogenic zones EZ (sources responsible of excessive discharges) would assist a neurologist during epilepsy diagnosis. Locating efficiently these abnormal sources among magnetoencephalography (MEG) biomarker is obtained by several inverse problem techniques. These techniques present different assumptions and particular epileptic network connectivity. Here, we proposed to evaluate performances of distributed inverse problem in defining EZ. First, we applied an advanced technique based on Singular Value Decomposition (SVD) to recover only pure transitory activities (interictal epileptiform discharges). We evaluated our technique’s robustness in separation between transitory and ripples versus frequency range, transitory shapes, and signal to noise ratio on simulated data (depicting both epileptic biomarkers and respecting time series and spectral properties of realistic data). We validated our technique on MEG signal using detector precision on 5 patients. Then, we applied four methods of inverse problem to define cortical areas and neural generators of excessive discharges. We computed network connectivity of each technique. Then, we confronted obtained noninvasive networks to intracerebral EEG transitory network connectivity using nodes in common, connection strength, distance metrics between concordant nodes of MEG and IEEG, and average propagation delay. Coherent Maximum Entropy on the Mean (cMEM) proved a high matching between MEG network connectivity and IEEG based on distance between active sources, followed by Exact low-resolution brain electromagnetic tomography (eLORETA), Dynamical Statistical Parametric Mapping (dSPM), and Minimum norm estimation (MNE). Clinical performance was interesting for entire methods providing in an average of 73.5% of active sources detected in depth and seen in MEG, and vice versa, about 77.15% of active sources were detected from MEG and seen in IEEG. Investigated problem techniques succeed at least in finding one part of seizure onset zone. dSPM and eLORETA depict the highest connection strength among all techniques. Propagation delay varies in this range [18, 25]ms, knowing that eLORETA ensures the lowest propagation delay (18 ms) and the closet one to IEEG propagation delay.

scholarly journals On the Implementation of Multi-bit Inexact Adder Cells and Application towards Image De-noising

2020 ◽  
Vol 24 (1) ◽  
Author(s):  
Srikant Kumar Beura ◽  
Amol Arjun Jawale ◽  
Bishnulatpam Pushpa Devi ◽  
Prabir Saha
Keyword(s):  
Signal To Noise Ratio ◽  
Substantial Reduction ◽  
Similarity Index ◽  
Digital Signal ◽  
Structural Similarity ◽  
Propagation Delay ◽  
Substantial Improvement ◽  
Structural Similarity Index ◽  
Error Metrics ◽  
And Performance

Inexact computing is an attractive concept for digital signal processing at the submicron regime. This paper proposes 2-bit inexact adder cell and further escalate to 4-bit, and 8-bit inexact adder and error metrics have been evaluated mathematically for such adder cells. The approximated design has been proposed through the simplification of the K-Maps, which leads to a substantial reduction in the propagation delay as well as energy consumption. The proposed design has been verified through the Cadence Spectre and performance parameters (such as delay, power consumption) have been evaluated through CMOS gpdk45 nm technology. Furthermore, the proposed design has been applied to image de-noising application where the performance of the images like Peak Signal to Noise Ratio (PSNR), Normalized Correlation Coefficient (NCC) and Structural Similarity Index (SSIM) has been analyzed through MATLAB, which offer the substantial improvement from its counterpart.

Atmospheric refraction effects in space vehicle tracking

1964 ◽  
Vol 54 (6B) ◽  
pp. 2185-2197
Author(s):  
R. A. Bowers
Keyword(s):  
Elevation Angle ◽  
Space Vehicle ◽  
Double Precision ◽  
Radio Waves ◽  
Atmospheric Refraction ◽  
Frequency Tracking ◽  
Analytic Expressions ◽  
Tracking Devices ◽  
Ray Bending ◽  
Derivatives Of

Abstract Refraction of radio waves in the atmosphere is becoming a topic of increasing concern to space scientists as tracking systems of extremely high precision are put into operation. Already ray bending and retardation of signal are many times greater than instrumental inaccuracies in measuring arrival time and elevation angle at the various tracking sites. A number of methods are presently in use for computation of the effects of atmospheric refraction on tracker measurements but all which have come to the writer's attention involve interpolation from tables, double precision methods on digital computers, or needlessly involved formulation. In this paper the mathematics of earthquake seismology are used to derive new analytic expressions for the effects of atmospheric refraction on the measurements of conventional radio frequency tracking devices. These expressions are concise, accurate, and rapidly evaluated in single precision. Expressions are also derived for the effects of refraction on time derivatives of the measurements, a subject which is virtually ignored in the literature.

scholarly journals Determination of Significant Wave Heights Using Damping Coefficients of Attenuated GNSS SNR Data from Static and Kinematic Observations

2019 ◽  
Vol 11 (4) ◽  
pp. 409 ◽  
Author(s):  
Ole Roggenbuck ◽  
Jörg Reinking ◽  
Tomke Lambertus
Keyword(s):  
Signal To Noise Ratio ◽  
Wave Model ◽  
Significant Wave ◽  
Sea Surface Roughness ◽  
Wave Heights ◽  
Gnss Reflectometry ◽  
Significant Wave Heights ◽  
Using Data ◽  
Ocean Remote Sensing

Currently, GNSS reflectometry based on the signal-to-noise ratio (SNR) has become an established tool in ocean remote sensing. Here, the distance between an antenna and the water surface is measured by analyzing the oscillation of the SNR observation. Due to the antenna gain pattern, this oscillation is more pronounced for satellite signals coming from low elevation angles. Additionally, the sea surface roughness is related to the attenuation of the SNR oscillation. Hence, the significant wave height (SWH) can be estimated by analyzing the SNR signal. In this work, a method is presented with which the SWH can be calculated from the attenuation’s damping coefficient of the SNR observations measured with surface-based receivers. The method’s usability is demonstrated using data from a static antenna operated in the German Bight and with data from a ship-based antenna. The estimated SWH values were validated against numerical wave model data. For both experiments, a high correlation was found.

scholarly journals Development and validation of comprehensive closed formulas for atmospheric delay and altimetry correction in ground-based GNSS-R

2021 ◽  
Author(s):  
Thalia Nikolaidou ◽  
Marcelo Santos ◽  
Simon Williams ◽  
Felipe Geremia-Nievinski
Keyword(s):  
Elevation Angle ◽  
Satellite System ◽  
Radio Waves ◽  
Atmospheric Refraction ◽  
Refraction Effect ◽  
Receiving Antenna ◽  
Coastal Sea ◽  
Global Navigation Satellite ◽  
Development And Validation ◽  
Atmospheric Delays

Radio waves used in Global Navigation Satellite System Reflectometry (GNSS-R) are subject to atmospheric refraction, even for ground-based tracking stations in applications such as coastal sea-level altimetry. Although atmospheric delays are best investigated via ray-tracing, its modification for reflections is not trivial. We have developed closed-form expressions for atmospheric refraction in ground-based GNSS-R and validated them against raytracing. We provide specific expressions for the linear and angular components of the atmospheric interferometric delay and corresponding altimetry correction, parameterized in terms of refractivity and bending angle. Assessment results showed excellent agreement for the angular component and good for the linear one. About half of the delay was found to originate above the receiving antenna at low satellite elevation angles. We define the interferometric slant factor used to map interferometric zenithal delays to individual satellites. We also provide an equivalent correction for the effective satellite elevation angle such that the refraction effect is nullified. Lastly, we present the limiting conditions for negligible atmospheric altimetry correction (sub-cm), over domain of satellite elevation angle and reflector height. For example, for 5-meter reflector height, observations below 20° elevation angle have more than 1-centimeter atmospheric altimetry error.

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