scholarly journals Amplifier Noise Based Optical Steganography with Coherent Detection

2014 ◽  
Vol 2 (1) ◽  
Author(s):  
Ben Wu ◽  
Matthew P. Chang ◽  
Naomi R. Caldwell ◽  
Myles E. Caldwell ◽  
Paul R. Prucnal
Keyword(s):  
Time Domain ◽  
Short Range ◽  
Review Paper ◽  
Signal To Noise Ratio ◽  
Random Phase ◽  
Coherent Detection ◽  
The Public ◽  
Key Space ◽  
Optical Delay ◽  
The Time Domain

AbstractWe summarize the principle and experimental setup of optical steganography based on amplified spontaneous emission (ASE) noise. Using ASE noise as the signal carrier, optical steganography effectively hides a stealth channel in both the time domain and the frequency domain. Coherent detection is used at the receiver of the stealth channel. Because ASE noise has short coherence length and random phase, it only interferes with itself within a very short range. Coherent detection requires the stealth transmitter and stealth receiver to precisely match the optical delay,which generates a large key space for the stealth channel. Several methods to further improve optical steganography, signal to noise ratio, compatibility with the public channel, and applications of the stealth channel are also summarized in this review paper.

scholarly journals A SFTD Algorithm for Optimizing the Performance of the Readout Strategy of Residence Time Difference Fluxgate

Sensors ◽  
2018 ◽  
Vol 18 (11) ◽  
pp. 3985 ◽  
Author(s):  
Siyu Chen ◽  
Yanzhang Wang ◽  
Jun Lin
Keyword(s):  
Residence Time ◽  
Time Domain ◽  
Signal To Noise Ratio ◽  
Low Frequency ◽  
Transformation Method ◽  
Time Difference ◽  
Single Frequency ◽  
Time Frequency ◽  
Frequency Magnetic Field ◽  
The Time Domain

Residence time difference (RTD) fluxgate sensor is a potential device to measure the DC or low-frequency magnetic field in the time domain. Nevertheless, jitter noise and magnetic noise severely affect the detection result. A novel post-processing algorithm for jitter noise reduction of RTD fluxgate output strategy based on the single-frequency time difference (SFTD) method is proposed in this study to boost the performance of the RTD system. This algorithm extracts the signal that has a fixed frequency and preserves its time-domain information via a time–frequency transformation method. Thereby, the single-frequency signal without jitter noise, which still contains the ambient field information in its time difference, is yielded. Consequently, compared with the traditional comparator RTD method (CRTD), the stability of the RTD estimation (in other words, the signal-to-noise ratio of residence time difference) has been significantly boosted with sensitivity of 4.3 μs/nT. Furthermore, the experimental results reveal that the RTD fluxgate is comparable to harmonic fluxgate sensors, in terms of noise floor.

Smoothing imaging condition for shot-profile migration

Geophysics ◽  
2007 ◽  
Vol 72 (3) ◽  
pp. S149-S154 ◽  
Author(s):  
Antoine Guitton ◽  
Alejandro Valenciano ◽  
Dimitri Bevc ◽  
Jon Claerbout
Keyword(s):  
Time Domain ◽  
Signal To Noise Ratio ◽  
Wiener Filter ◽  
Window Size ◽  
Trial And Error ◽  
Data Set ◽  
Smoothing Operator ◽  
Imaging Condition ◽  
Damping Parameter ◽  
The Time Domain

Amplitudes in shot-profile migration can be improved if the imaging condition incorporates a division (deconvolution in the time domain) of the upgoing wavefield by the downgoing wavefield. This division can be enhanced by introducing an optimal Wiener filter which assumes that the noise present in the data has a white spectrum. This assumption requires a damping parameter, related to the signal-to-noise ratio, often chosen by trial and error. In practice, the damping parameter replaces the small values of the spectrum of the downgoing wavefield and avoids division by zero. The migration results can be quite sensitive to the damping parameter, and in most applications, the upgoing and downgoing wavefields are simply multiplied. Alternatively, the division can be made stable by filling the small values of thespectrum with an average of the neighboring points. This averaging is obtained by running a smoothing operator on the spectrum of the downgoing wavefield. This operation called the smoothing imaging condition. Our results show that where the spectrum of the downgoing wavefield is high, the imaging condition with damping and smoothing yields similar results, thus correcting for illumination effects. Where the spectrum is low, the smoothing imaging condition tends to be more robust to the noise level present in the data, thus giving better images than the imaging condition with damping. In addition, our experiments indicate that the parameterization of the smoothing imaging condition, i.e., choice of window size for the smoothing operator, is easy and repeatable from one data set to another, making it a valuable addition to our imaging toolbox.

scholarly journals Time-expanded phase-sensitive optical time-domain reflectometry

2021 ◽  
Vol 10 (1) ◽  
Author(s):  
Miguel Soriano-Amat ◽  
Hugo F. Martins ◽  
Vicente Durán ◽  
Luis Costa ◽  
Sonia Martin-Lopez ◽  
...  
Keyword(s):  
Time Domain ◽  
Signal To Noise Ratio ◽  
Random Phase ◽  
Environmental Variable ◽  
Time Domain Reflectometry ◽  
Trade Offs ◽  
Optical Time Domain Reflectometry ◽  
Phase Sensitive ◽  
Spatio Temporal ◽  
Optical Time

AbstractPhase-sensitive optical time-domain reflectometry (ΦOTDR) is a well-established technique that provides spatio-temporal measurements of an environmental variable in real time. This unique capability is being leveraged in an ever-increasing number of applications, from energy transportation or civil security to seismology. To date, a wide number of different approaches have been implemented, providing a plethora of options in terms of performance (resolution, acquisition bandwidth, sensitivity or range). However, to achieve high spatial resolutions, detection bandwidths in the GHz range are typically required, substantially increasing the system cost and complexity. Here, we present a novel ΦOTDR approach that allows a customized time expansion of the received optical traces. Hence, the presented technique reaches cm-scale spatial resolutions over 1 km while requiring a remarkably low detection bandwidth in the MHz regime. This approach relies on the use of dual-comb spectrometry to interrogate the fibre and sample the backscattered light. Random phase-spectral coding is applied to the employed combs to maximize the signal-to-noise ratio of the sensing scheme. A comparison of the proposed method with alternative approaches aimed at similar operation features is provided, along with a thorough analysis of the new trade-offs. Our results demonstrate a radically novel high-resolution ΦOTDR scheme, which could promote new applications in metrology, borehole monitoring or aerospace.

Multiscale Estimation of Event Arrival Times and Their Uncertainties in Hydroacoustic Records from Autonomous Oceanic Floats

2020 ◽  
Vol 110 (3) ◽  
pp. 970-997 ◽  
Author(s):  
Joel D. Simon ◽  
Frederik J. Simons ◽  
Guust Nolet
Keyword(s):  
Time Series ◽  
Time Domain ◽  
Signal To Noise Ratio ◽  
Information Criterion ◽  
Arrival Times ◽  
Timing Uncertainty ◽  
Error Distributions ◽  
Marine Areas ◽  
Signal Segment ◽  
The Time Domain

ABSTRACT We describe an algorithm to pick event onsets in noisy records, characterize their error distributions, and derive confidence intervals on their timing. Our method is based on an Akaike information criterion that identifies the partition of a time series into a noise and a signal segment that maximizes the signal-to-noise ratio. The distinctive feature of our approach lies in the timing uncertainty analysis, and in its application in the time domain and in the wavelet timescale domain. Our novel data are records collected by freely floating Mobile Earthquake Recording in Marine Areas by Independent Divers (MERMAID) instruments, midcolumn hydrophones that report triggered segments of ocean-acoustic time series.

One parameter binary black hole inverse problem using a sparse training set

2018 ◽  
Vol 27 (04) ◽  
pp. 1850043 ◽  
Author(s):  
M. Carrillo ◽  
M. Gracia-Linares ◽  
J. A. González ◽  
F. S. Guzmán
Keyword(s):  
Black Hole ◽  
Time Domain ◽  
Signal To Noise Ratio ◽  
Small Sample ◽  
Mass Ratio ◽  
Training Set ◽  
The Core ◽  
Binary Black Hole ◽  
Orbital Phase ◽  
The Time Domain

In this paper, we use Artificial Neural Networks (ANNs) to estimate the mass ratio [Formula: see text] in a binary black hole collision out of the gravitational wave (GW) strain. We assume the strain is a time series (TS) that contains a part of the orbital phase and the ring-down of the final black hole. We apply the method to the strain itself in the time domain and also in the frequency domain. We present the accuracy in the prediction of the ANNs trained with various values of signal-to-noise ratio (SNR). The core of our results is that the estimate of the mass ratio is obtained with a small sample of training signals and resulting in predictions with errors of the order of 1% for our best ANN configurations.

scholarly journals Reduction of Phase Noise in Interferometry with State-space Analysis

1979 ◽  
Vol 49 ◽  
pp. 103-110
Author(s):  
Ali Okatan ◽  
J. P. Basart
Keyword(s):  
Phase Noise ◽  
Time Domain ◽  
Signal To Noise Ratio ◽  
Signal To Noise ◽  
State Space Analysis ◽  
The Common ◽  
The Time Domain ◽  
Fringe Frequency ◽  
Incoherent Averaging ◽  
Averaging Techniques

In radio mapping, one of the problems encountered is the random bias in the visibility estimate. The bias can be divided into two parts: (a) the positive bias due to the common sky background seen by all elements of the interferometer, and (b) the negative bias due to phase noise present in the system. The first kind of bias can be easily removed by subtracting the correlation between the signals at two interferometer sites when the source is not in the antenna beams from that measured with the source in the antenna beams. This bias will therefore not be considered here. In contrast, the second kind of bias is more difficult to remove. When the signal-to-noise ratio of the interferometer system is high, incoherent averaging techniques can be utilized in the fringe frequency or in the time domain (Clark et al., 1969; Moran, 1973).

scholarly journals Fourier-transform spatial modulation spectroscopy of single gold nanorods

Nanophotonics ◽  
2018 ◽  
Vol 7 (4) ◽  
pp. 715-726 ◽  
Author(s):  
Heiko Kollmann ◽  
Martin Esmann ◽  
Julia Witt ◽  
Aleksandra Markovic ◽  
Vladimir Smirnov ◽  
...  
Keyword(s):  
Fourier Transform ◽  
Gold Nanorods ◽  
Time Resolution ◽  
Time Domain ◽  
Signal To Noise Ratio ◽  
Spatial Modulation ◽  
High Signal ◽  
Extinction Cross Section ◽  
Modulation Spectroscopy ◽  
The Time Domain

AbstractSensing the scattered fields of single metallic nanostructures is a crucial step towards the applications of isolated plasmonic antennas, such as for the sensing of single molecules or nanoparticles. In the past, both near- and far-field spectroscopy methods have been applied to monitor single plasmonic resonances. So far, however, these spectral-domain techniques do not yet provide the femtosecond time resolution that is needed to probe the dynamics of plasmonic fields in the time domain. Here, we introduce a time-domain technique that combines broadband Fourier-transform spectroscopy and spatial modulation spectroscopy (FT-SMS) to quantitatively measure the extinction spectra of the isolated gold nanorods with a nominal footprint of 41×10 nm2. Using a phase-stable pulse pair for excitation, the technique is capable of rejecting off-resonant stray fields and providing absolute measurements of the extinction cross section. Our results indicate that the method is well suited for measuring the optical response of strongly coupled hybrid systems with high signal-to-noise ratio. It may form the basis for new approaches towards time-domain spectroscopy of single nanoantennas with few-cycle time resolution.

Stellar Variability: from Citizen Science to Citizen Astronomy

2017 ◽  
Vol 14 (S339) ◽  
pp. 215-219
Author(s):  
S. Kafka ◽  
E. Griffin
Keyword(s):  
Citizen Science ◽  
Time Domain ◽  
Public Understanding Of Science ◽  
Public Understanding ◽  
Active Engagement ◽  
Sky Surveys ◽  
The Public ◽  
Science Projects ◽  
Understanding Of Science ◽  
The Time Domain

AbstractThe contribution of citizens to research is irrefutable. Especially this century with the outburst of all-sky surveys, professional astronomers use citizen-science projects to engage the public in analysing and sorting large quantities of data, often leading to noteworthy discoveries. From crowdsourcing to acquiring data, citizens are leaving a significant mark in the science landscape, assisting professional astronomers with their work. In turn, citizen science is a means of increasing science literacy and public understanding of science. At the same time, the time domain enables a more active engagement of backyard observers in research. Citizen astronomers not only take data, but also reduce and analyse them, and participate in preparing scientific manuscripts.

Advantageous Apodization Functions for Magnitude-Mode Fourier Transform Spectroscopy

1987 ◽  
Vol 41 (1) ◽  
pp. 93-98 ◽  
Author(s):  
Judy P. Lee ◽  
Melvin B. Comisarow
Keyword(s):  
Fourier Transform ◽  
Time Domain ◽  
Dynamic Range ◽  
Signal To Noise Ratio ◽  
Time Domain Signal ◽  
Time Domain Data ◽  
Window Functions ◽  
Fourier Transform Spectra ◽  
The Time Domain ◽  
Ratio Reduction

A systematic examination of the efficacy of window functions for reducing the spectral skirt of magnitude-mode Fourier transform spectra is reported. The efficacy is examined for the general case of a damped time-domain signal, with specific cases ranging from undamped to essentially completely damped signals. The choice of the optimal window is dependent upon the required dynamic range and the amount of damping in the time-domain data. For a dynamic range of less than 100:1 and moderate damping, the Hamming window is the window of choice. For larger dynamic ranges or greater damping, the 3-term Blackman-Harris window and the Kaiser-Bessel window are the windows of choice. The 3-term Blackman-Harris window is preferred for a dynamic range of 1,000:1 and the Kaiser-Bessel window is preferred for a dynamic range of 10,000:1. The sensitivity (signal-to-noise ratio) reduction for windows is reported for a damping range from zero to essentially complete damping. All windows examined have the same sensitivity reduction within 25%.

scholarly journals A Novel Channel Calibration Method for Bistatic ISAR Imaging System

2018 ◽  
Vol 8 (11) ◽  
pp. 2160 ◽  
Author(s):  
Lin Shi ◽  
Baofeng Guo ◽  
Juntao Ma ◽  
Chaoxuan Shang ◽  
Huiyan Zeng
Keyword(s):  
Time Domain ◽  
Pulse Compression ◽  
Imaging System ◽  
Signal To Noise Ratio ◽  
Calibration Method ◽  
Imaging Systems ◽  
Calibration Coefficient ◽  
Channel Characteristics ◽  
Isar Imaging ◽  
The Time Domain

In practical bistatic inverse synthetic aperture radar (ISAR) imaging systems, the echo signals are modulated by non-ideal amplitude and phase characteristics of the transmitting and receiving channels, which seriously distorts image quality. However, the conventional channel calibration method based on a transponder is not applicable to bistatic ISAR imaging systems, since the baseline of the system is up to hundreds of kilometers. A channel calibration method only using calibration satellite echo information is proposed for the system, with a linear frequency modulation (LFM) waveform. Firstly, echoes of the calibration satellite are collected by tracking the satellite and multi-period echoes are aligned in the time domain, according to the pulse compression result. Then, the signal to noise ratio (SNR) is improved by accumulating multi-period echoes coherently in the time domain and the calibration coefficient is constructed based on the accumulated signal. Finally, spectrum of the echo signal is multiplied with the calibration coefficient to compensate the influence of channel characteristics. The effectiveness of the proposed method is verified by the simulation experiment with real satellite echoes.

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