The Experts below are selected from a list of 312 Experts worldwide ranked by ideXlab platform
Sandip K Chakrabarti - One of the best experts on this subject based on the ideXlab platform.
-
effective recombination coefficient and solar zenith angle effects on low latitude d region ionosphere evaluated from vlf Signal Amplitude and its time delay during x ray solar flares
arXiv: Space Physics, 2013Co-Authors: Tamal Basak, Sandip K ChakrabartiAbstract:Excess solar X-ray radiation during solar flares causes an enhancement of ionization in the ionospheric D-region and hence affects sub-ionospherically propagating VLF Signal Amplitude and phase. In first part of the work, using the well known LWPC technique, we simulated the flare induced excess lower ionospheric electron density by Amplitude perturbation method. Unperturbed D-region electron density is also obtained from simulation and compared with IRI-model results. Using these simulation results and time delay as key parameters, we calculate the effective electron recombination coefficient ($\alpha_{eff}$) at solar flare peak region. Our results match with the same obtained by other established models. In the second part, we dealt with the solar zenith angle effect on D-region during flares. We relate this VLF data with the solar X-ray data. We find that the peak of the VLF Amplitude occurs later than the time of the X-ray peak for each flare. We investigate this so-called time delay ($\bigtriangleup t$). For the C-class flares we find that there is a direct correspondence between $\bigtriangleup t$ of a solar flare and the average solar zenith angle $Z$ over the Signal propagation path at flare occurrence time. Now for deeper analysis, we compute the $\bigtriangleup t$ for different local diurnal time slots $DT$. We find that while the time delay is anti-correlated with the flare peak energy flux $\phi_{max}$ independent of these time slots, the goodness of fit, as measured by $reduced$-$\chi^2$, actually worsens as the day progresses. The variation of the $Z$ dependence of $reduced$-$\chi^2$ seems to follow the variation of standard deviation of $Z$ along the $T_x$-$R_x$ propagation path. In other words, for the flares having almost constant $Z$ over the path a tighter anti-correlation between $\bigtriangleup t$ and $\phi_{max}$ was observed.
-
effective recombination coefficient and solar zenith angle effects on low latitude d region ionosphere evaluated from vlf Signal Amplitude and its time delay during x ray solar flares
Astrophysics and Space Science, 2013Co-Authors: Tamal Basak, Sandip K ChakrabartiAbstract:Excess solar X-ray radiation during solar flares causes an enhancement of ionization in the ionospheric D-region and hence affects sub-ionospherically propagating VLF Signal Amplitude and phase. VLF Signal Amplitude perturbation (ΔA) and Amplitude time delay (Δt) (vis-a-vis corresponding X-ray light curve as measured by GOES-15) of NWC/19.8 kHz Signal have been computed for solar flares which is detected by us during Jan–Sep 2011. The Signal is recorded by SoftPAL facility of IERC/ICSP, Sitapur (22∘ 27′N, 87∘ 45′E), West Bengal, India. In first part of the work, using the well known LWPC technique, we simulated the flare induced excess lower ionospheric electron density by Amplitude perturbation method. Unperturbed D-region electron density is also obtained from simulation and compared with IRI-model results. Using these simulation results and time delay as key parameters, we calculate the effective electron recombination coefficient (αeff) at solar flare peak region. Our results match with the same obtained by other established models. In the second part, we dealt with the solar zenith angle effect on D-region during flares. We relate this VLF data with the solar X-ray data. We find that the peak of the VLF Amplitude occurs later than the time of the X-ray peak for each flare. We investigate this so-called time delay (Δt). For the C-class flares we find that there is a direct correspondence between Δt of a solar flare and the average solar zenith angle Z over the Signal propagation path at flare occurrence time. Now for deeper analysis, we compute the Δt for different local diurnal time slots DT. We find that while the time delay is anti-correlated with the flare peak energy flux ϕmax independent of these time slots, the goodness of fit, as measured by reduced-χ2, actually worsens as the day progresses. The variation of the Z dependence of reduced-χ2 seems to follow the variation of standard deviation of Z along the Tx-Rx propagation path. In other words, for the flares having almost constant Z over the path a tighter anti-correlation between Δt and ϕmax was observed.
Gordon R. J. Cooper - One of the best experts on this subject based on the ideXlab platform.
-
Applications of the Fractional Order Analytic Signal Amplitude and Local Wavenumber
78th EAGE Conference and Exhibition 2016, 2016Co-Authors: Gordon R. J. CooperAbstract:Analytic expressions for the fractional order anomaly, analytic Signal Amplitude, and local wavenumber of different magnetic models are derived. These expressions can be integrated with existing source-distance methods and used as part of the semi-automatic interpretation of magnetic anomalies. The order of the fractional order derivatives can be chosen based on the noise levels of the data.
-
Using the analytic Signal Amplitude to determine the location and depth of thin dikes from magnetic data
GEOPHYSICS, 2015Co-Authors: Gordon R. J. CooperAbstract:ABSTRACTA semiautomatic method to determine the location and depth of thin dykes is introduced. The ratio of analytic Signal Amplitudes of orders 0 and 1 of the magnetic anomaly from a thin dike was used to give the distance r to the dike. Local minima of r gave the depth to the dike, and the position of these minima gave its horizontal location. Because in the method we used just the magnetic field and its first-order derivatives, it was less sensitive to noise than were higher order derivative-based methods. Once the position of the dike has been determined, then its dip and susceptibility-thickness product can be calculated from the analytic Signal Amplitude, providing that the magnetization vector is known.
-
Reducing the dependence of the analytic Signal Amplitude of aeromagnetic data on the source vector direction
GEOPHYSICS, 2014Co-Authors: Gordon R. J. CooperAbstract:ABSTRACTThe analytic Signal Amplitude (As) is commonly used as an edge-detection filter for aeromagnetic data. For profile (2D) data, its shape is independent of the source magnetization vector direction, but this is not the case for map (3D) data. A modified analytic Signal Amplitude (TAS) is introduced here which has a much reduced dependence on this vector for both contact and dike models. When the modified analytic Signal Amplitude was applied to synthetic data sets, it was more effective in enhancing the edges of the bodies than the standard As. Because it uses second-order derivatives of the magnetic field, the method is sensitive to noise and so an additional formulation was developed for noisy data sets that only use first-order derivatives.
-
Reducing The Dependence Of The Analytic Signal Amplitude Of Aeromagnetic Data On The Source Vector Direction
2013Co-Authors: Gordon R. J. CooperAbstract:The analytic Signal Amplitude (As) is a commonly used edge detection filter for aeromagnetic data. For profile data its response is independent of the source magnetisation vector direction, but this is not the case for map data. A modified As is inroduced here which has a much reduced dependance on the source magnetisation vector direction. Because it uses second order derivatives the method is sensitive to noise. The modified As is demonstrated on synthetic datasets and on an aeromagnetic dataset from South Africa.
Tamal Basak - One of the best experts on this subject based on the ideXlab platform.
-
effective recombination coefficient and solar zenith angle effects on low latitude d region ionosphere evaluated from vlf Signal Amplitude and its time delay during x ray solar flares
arXiv: Space Physics, 2013Co-Authors: Tamal Basak, Sandip K ChakrabartiAbstract:Excess solar X-ray radiation during solar flares causes an enhancement of ionization in the ionospheric D-region and hence affects sub-ionospherically propagating VLF Signal Amplitude and phase. In first part of the work, using the well known LWPC technique, we simulated the flare induced excess lower ionospheric electron density by Amplitude perturbation method. Unperturbed D-region electron density is also obtained from simulation and compared with IRI-model results. Using these simulation results and time delay as key parameters, we calculate the effective electron recombination coefficient ($\alpha_{eff}$) at solar flare peak region. Our results match with the same obtained by other established models. In the second part, we dealt with the solar zenith angle effect on D-region during flares. We relate this VLF data with the solar X-ray data. We find that the peak of the VLF Amplitude occurs later than the time of the X-ray peak for each flare. We investigate this so-called time delay ($\bigtriangleup t$). For the C-class flares we find that there is a direct correspondence between $\bigtriangleup t$ of a solar flare and the average solar zenith angle $Z$ over the Signal propagation path at flare occurrence time. Now for deeper analysis, we compute the $\bigtriangleup t$ for different local diurnal time slots $DT$. We find that while the time delay is anti-correlated with the flare peak energy flux $\phi_{max}$ independent of these time slots, the goodness of fit, as measured by $reduced$-$\chi^2$, actually worsens as the day progresses. The variation of the $Z$ dependence of $reduced$-$\chi^2$ seems to follow the variation of standard deviation of $Z$ along the $T_x$-$R_x$ propagation path. In other words, for the flares having almost constant $Z$ over the path a tighter anti-correlation between $\bigtriangleup t$ and $\phi_{max}$ was observed.
-
effective recombination coefficient and solar zenith angle effects on low latitude d region ionosphere evaluated from vlf Signal Amplitude and its time delay during x ray solar flares
Astrophysics and Space Science, 2013Co-Authors: Tamal Basak, Sandip K ChakrabartiAbstract:Excess solar X-ray radiation during solar flares causes an enhancement of ionization in the ionospheric D-region and hence affects sub-ionospherically propagating VLF Signal Amplitude and phase. VLF Signal Amplitude perturbation (ΔA) and Amplitude time delay (Δt) (vis-a-vis corresponding X-ray light curve as measured by GOES-15) of NWC/19.8 kHz Signal have been computed for solar flares which is detected by us during Jan–Sep 2011. The Signal is recorded by SoftPAL facility of IERC/ICSP, Sitapur (22∘ 27′N, 87∘ 45′E), West Bengal, India. In first part of the work, using the well known LWPC technique, we simulated the flare induced excess lower ionospheric electron density by Amplitude perturbation method. Unperturbed D-region electron density is also obtained from simulation and compared with IRI-model results. Using these simulation results and time delay as key parameters, we calculate the effective electron recombination coefficient (αeff) at solar flare peak region. Our results match with the same obtained by other established models. In the second part, we dealt with the solar zenith angle effect on D-region during flares. We relate this VLF data with the solar X-ray data. We find that the peak of the VLF Amplitude occurs later than the time of the X-ray peak for each flare. We investigate this so-called time delay (Δt). For the C-class flares we find that there is a direct correspondence between Δt of a solar flare and the average solar zenith angle Z over the Signal propagation path at flare occurrence time. Now for deeper analysis, we compute the Δt for different local diurnal time slots DT. We find that while the time delay is anti-correlated with the flare peak energy flux ϕmax independent of these time slots, the goodness of fit, as measured by reduced-χ2, actually worsens as the day progresses. The variation of the Z dependence of reduced-χ2 seems to follow the variation of standard deviation of Z along the Tx-Rx propagation path. In other words, for the flares having almost constant Z over the path a tighter anti-correlation between Δt and ϕmax was observed.
Paolo Braca - One of the best experts on this subject based on the ideXlab platform.
-
Signal Amplitude Estimation and Detection From Unlabeled Binary Quantized Samples
IEEE Transactions on Signal Processing, 2018Co-Authors: Guanyu Wang, Rick S. Blum, Peter Willett, Stefano Marano, Vincenzo Matta, Paolo BracaAbstract:Signal Amplitude estimation and detection from unlabeled quantized binary samples are studied, assuming that the order of the time indexes is completely unknown. First, maximum likelihood (ML) estimators are utilized to estimate both the permutation matrix and unknown Signal Amplitude under arbitrary but known Signal shape and quantizer thresholds. Sufficient conditions are provided, under which an ML estimator can be found in polynomial time, and an alternating maximization algorithm is proposed to solve the general problem via good initialization. In addition, the statistical identifiability of the model is studied. Furthermore, an approximation of the generalized likelihood ratio test detector is adopted to detect the presence of the Signal. In addition, an accurate approximation of the probability of successful permutation matrix recovery is derived, and explicit expressions are provided to reveal the relationship between the Signal length and the number of quantizers. Finally, numerical simulations are performed to verify the theoretical results.
S.k. Nath - One of the best experts on this subject based on the ideXlab platform.
-
Effect of variation in Signal Amplitude and transit time on reliability analysis of ultrasonic time of flight diffraction characterization of vertical and inclined cracks.
Ultrasonics, 2013Co-Authors: S.k. NathAbstract:The variation of Amplitude and transit time of the diffracted Signal from the crack-tip in complex geometry components and their resulting effect on the probability of detection (POD) and probability of sizing (POS) was studied. The diffracted Signal Amplitude has been evaluated from the standard expressions for diffraction coefficient, spatial attenuation and the transit time from the respective mathematical models for both vertical and inclined cracks. The same parameters namely the Signal Amplitude and the transit time have been measured through experiments conducted on simulated test specimens. It has been observed that the analytical and experimental results compare well with each other. Based on this result the trend and shape (width of the transition zone) of the POD/POS curves can be predicted.
