Natural Noise Level Research Articles

Analyzing the accuracy of detecting steganograms formed by adaptive steganographic methods when using artificial neural networks

This paper reports a comparative analysis of accuracy in the detection of steganograms formed according to adaptive steganographic methods, using steganography detectors based on common and specialized types of artificial neural networks. The results of the review of modern convolutional neural networks applied for the tasks of digital image stegoanalysis have established that the accuracy of operating the steganography detectors based on these networks is significantly compromised when processing image packets characterized by a significant variability of statistical parameters. The performance accuracy of steganography detectors based on the modern statistical model of container images maxSRMd2 has been investigated, as well as on the latest convolutional and «hybrid» artificial neural networks, in particular, GB-Ras and ASSAF networks, when detecting steganograms formed according to the adaptive steganographic methods HUGO and MiPOD. It was established that the use of the statistical model maxSRMd2 makes it possible to significantly (up to 30 %) improve the accuracy of steganogram detection in the case of analyzing those images that are characterized by a high level of natural noise. It was found that the use of the ASSAF network makes it possible to significantly (up to 35 %) reduce an error of steganogram detection compared to current steganography detectors based on the GB-Ras network and the maxSRMd2 statistical model. It was determined that the high accuracy of the ASSAF network-based steganography detector is maintained even in the most difficult case of image processing with high noise and poor filling of the container image with stegodata (less than 10 %). The results reported here are of theoretical interest for designing high-precision steganography detectors capable of working under conditions of high variability in image parameters.

Roaring and repetition: How bowhead whales adjust their call density and source level (Lombard effect) in the presence of natural and seismic airgun survey noise.

Over 500 000 automated and manual acoustic localizations, measured over seven years between 2008 and 2014, were used to examine how natural wind-driven noise and anthropogenic seismic airgun survey noise influence bowhead whale call densities (calls/km2/min) and source levels during their fall migration in the Alaskan Beaufort Sea. Noise masking effects, which confound measurements of behavioral changes, were removed using a modified point transect theory. The authors found that mean call densities generally rose with increasing continuous wind-driven noise levels. The occurrence of weak airgun pulse sounds also prompted an increase in call density equivalent to a 10-15 dB change in natural noise level, but call density then dropped substantially with increasing cumulative sound exposure level (cSEL) from received airgun pulses. At low in-band noise levels the mean source level of the acoustically-active population changed to nearly perfectly compensate for noise increases, but as noise levels increased further the mean source level failed to keep pace, reducing the population's communication space. An increase of >40 dB cSEL from seismic airgun activity led to an increase in source levels of just a few decibels. These results have implications for bowhead acoustic density estimation, and evaluations of the masking impacts of anthropogenic noise.

Estimation of self noise of geomagnetic and geoelectric field sensors using multichannel measurement method

Results of synchronous electric and magnetic fields measurements made by different types of sensors in the frequency range of 0.002–7000 Hz are covered. Different approaches to obtaining the evaluation of sensor noise are considered. The technique of quantitative estimation of level of natural noise of each sensor and characteristics of a natural field on the basis of two- and three-channel scheme of synchronous measurement is given. Comparison of experimental noise estimations with computational ones is given. It is shown that the magnetometer based on magnetomodulation transducer has an unacceptably high level of its self noise for using it in applications related to the measurement of natural geomagnetic field.

Conflicting sounds in natural recreation areas—An historical Minnesota perspective

Minnesota has long seen battles between conflicting activities in natural recreation areas. Snowmobiles were first introduced in the 1960 by two Minnesota firms. By the 1970s physical and noise impacts had increased and a state committee to address trail uses and conflicts was established. In the same time period, a large scale environmental impact study on effects of copper-nickel mining on the BWCAW and national forest was initiated. A noise model was developed by Moorhead State staff that compared mining noise with natural noise levels. This issue rested until 2007 when exploration drilling started 24/7 in the Superior Nation Forest and near the BWCAW. Extensive monitoring and modeling efforts were undertaken by the companies and the Forest Service and limits established on acceptable noise levels. The snowmobile noise problem has not gone away with periodic controversy and assessment. To the south, the Saint Croix National Scenic Riverway (NPS) and the Minnesota Valley National Wildlife Refuge (USFWS) have both addressed potential noise intrusion from adjacent sand and gravel mining activities. Of course, the BWCAW was the center of long term disputes over noise, with motors now limited to only a few lakes and low altitude aircraft flights prohibited.

Exploiting natural surface noise and ships as sources of opportunity for passive bottom reflection-loss estimation

The marine ambient-noise field, including natural and anthropogenic sources, can be exploited to estimate the bottom reflection coefficient and the associated loss, which is an important contributor to the total transmission loss in shallow water scenarios. The physical nature of the natural surface-noise field is such that the bottom reflection coefficient can be estimated passively by beamforming on a vertical line array, if there are no localized sources near the array and the noise level generated by waves and wind is adequate. Recently, an algorithm for processing the noise generated by a single ship moving over a wide range of steering angles has been shown to extend the technique to this source of opportunity, even when the natural noise level is too low to produce any measurable loss. In this study, simulation and data from recent experimental campaigns (from arrays moored to the bottom or mounted on an autonomous underwater vehicle) are used to illustrate the technique, and investigate in particular both the effect on the performance of low natural noise levels, and the possibility of using more than one ship as source of opportunity.

Assessment of the proportion of anthropogenic underwater noise levels in passive acoustic monitoring

The marine environment faces a pressure from the increasing shipping intensity in the form of rising levels of continuous anthropogenic underwater noise. Current underwater noise monitoring guidelines advise to measure the long-term trends in the overall noise levels in the frequency bands where ship noise is most prevalent. However, the natural noise is omnipresent and prolongs the time period required for the detection of statistically significant trends in the overall noise. The monitoring efficiency can be improved by finding the proportions of the anthropogenic and the natural noise levels and by measuring the changes in the proportions over time. These proportions can be found by differentiating between the two types of ambient noise in the recordings according to both proximity of the ships and the variability of the environmental conditions. This is achieved by using the AIS ship traffic data along with the ship noise detection algorithms. The AIS data enable to determine the position of ships around a noise monitoring location and calibrate the ship noise detection algorithms. The results and the methods are presented for the passive acoustic monitoring in the Baltic Sea and applicability of the described methods are discussed.

Speaker recognition regardless of context and language on a fixed set of competitors

The problem of speaker recognition from a given set of speakers for any language and any context is considered. A database of Russian numerals that contains speech segments from 216 men and 177 women, each of whom spoke from 400 to 800 words, is used for recognition. Speech has been recorded on different types of microphones in different rooms at the natural noise level. Recognition is based on solutions of the inverse problem of finding the voice excitation pulse shape for each pitch period by the known speech segment. The pulse shape is defined as the inverse Fourier transform of the regularized ratio of speech signal spectra at the intervals of the open and closed glottis. Recognition is carried out by ten parameters: the pitch period, the open glottis interval duration, times when the source amplitude is maximum, minimum, or zero, the amplitude ratio for the minimum and maximum source pulses, three decomposition ratios of the source function by the principal component method, and the vowel duration. In such a recognition procedure, in the case of the utterance of a word that contains one vowel, the false reject rate (FRR) for men is 1.7---5.4%, and the false acceptance rate (FAR) is 5.4---7.1%. For women FRR = 2---5.2% and FAR = 5.2---6.3%. The recognition error decreases with an increasing number of vowels in the speech signal. At 10 vowels, for men FRR = 0.05---0.2% and FAR = 0.07---0.8%, and for women FRR = 0.09---0.2% and FAR = 0.17---2.1%.

Little effect of natural noise on high-frequency hearing in frogs, Odorrana tormota.

Ambient noise influences acoustic communication in animals. The concave-eared frogs (Odorrana tormota) produce high-frequency sound signals to avoid potential masking from noise. However, whether environmental noise has effect on the high-frequency hearing of frogs is largely unclear. By measuring the auditory evoked near-field potentials (AENFPs) from the torus semicircularis of the midbrain at frequencies 1-23kHz in the presence of three noise levels, we found no significant difference in the peak-to-peak amplitude, threshold and latency of AENFP between low-level (35dB SPL) background noise and mid-level (65dB SPL) broadcast natural noise. For a natural noise level of 85dB SPL, AENFP amplitude decreased and threshold and latency increased at frequencies 3-13kHz. Spike counts evoked by stimuli at the best excitatory frequency under 85dB SPL natural noise exposure were lower in 7-kHz CF neurons than in exposures to 35 and 65dB SPL noise. However spike counts were similar for 14- and 20-kHz CF neurons at the three exposure levels. These findings indicate that environmental noise does not mask the responses of high-frequency tuned auditory neurons, and suggest that the acoustic communication system of O. tormota is efficiently adapted to noisy habitats.

ELF/VLF Perturbations Above the Haarp Transmitter Recorded by the Demeter Satellite in the Upper Ionosphere

In the studies of the data received from DEMETER (orbit altitude above the Earth is about 700 km), we detected for the first time electromagnetic perturbations, which are due to the ionospheric modification by HAARP, a high-power high-frequency transmitter, simultaneously in the extremely low-frequency (ELF, below 1200 Hz) and very low-frequency (VLF, below 20 kHz) ranges. Of the thirteen analyzed flybys of the satellite above the heated area, the ELF/VLF signals were detected in three cases in the daytime (LT = 11–12 h), when the minimum distance between the geomagnetic projections of the satellite and the heated area center on the Earth’s surface did not exceed 31 km. During the nighttime flybys, the ELF/VLF perturbations were not detected. The size of the perturbed region was about 100 km. The amplitude, spectrum, and polarization of the ELF perturbations were analyzed, and their comparison with the characteristics of natural ELF noise above the HAARP transmitter was performed. In particular, it was shown that in the daytime the ELF perturbation amplitude above the heated area can exceed by a factor of 3 to 8 the amplitude of natural ELF noise. The absence of the nighttime records of artificial ELF/VLF perturbations above the heated area can be due to both the lower frequency of the heating signal, at which the heating occurs in the lower ionosphere, and the higher level of natural noise. The spectrum of the VLF signals related to the HAARP transmitter operation had two peaks at frequencies of 8 to 10 kHz and 15 to 18 kHz, which are close to the first and second harmonics of the lower-hybrid resonance in the heated area. The effect of the whistler wave propagation near the lower-hybrid resonance region on the perturbation spectrum recorded in the upper ionosphere for these signals has been demonstrated. In particular, some of the spectrum features can be explained by assuming that the VLF signals propagate in quasiresonance, rather than quasilongitudinal, regime. It is noted that the profile and dynamics of the ELF perturbation frequency spectrum conform to the assumption of their connection with quasistatic small-scale electron-density inhomogeneities occurring in the heated region and having lifetimes of a few seconds or more. The possible mechanisms of the ELF/VLF perturbation formation in the ionospheric plasma above the high-latitude HAARP facility at the DEMETER flyby altitudes are discussed.

Empirical evaluation of microtremor H/V spectral ratio

The objective of this work is to perform a purely empirical assessment of the actual capabilities of the horizontal-to-vertical (H/V) spectral ratio technique to provide reliable and relevant information concerning site conditions and/or site amplification. This objective has been tackled through the homogeneous (re)processing of a large volume of earthquakes and ambient noise data recorded by different research teams in more than 200 sites located mainly in Europe, but also in the Caribbean and in Tehran. The original recordings were first gathered in a specific database with information on both the sites and recorded events. Then, for all sites close to an instrumented reference, average site-to-reference spectral ratios (“spectral ratio method” (SSR)) were derived in a homogeneous way (window selection, smoothing, signal-to-noise ratio threshold, averaging), as well as H/V ratios (“HVSRE–RF”) on earthquake recordings. H/V ratios were also obtained from noise recordings at each site (either specific measurements, or extracted from pre- or post-event noise windows). The spectral curves resulting from these three techniques were estimated reliable for a subset of 104 sites, and were thus compared in terms of fundamental frequency, amplitude and amplification bandwidth, exhibiting agreements and disagreements, for which interpretations are looked for in relation with characteristics of site conditions. The first important result consists in the very good agreement between fundamental frequencies obtained with either technique, observed for 81% of the analyzed sites. A significant part of the disagreements correspond to thick, low frequency, continental sites where natural noise level is often very low and H/V noise ratios do not exhibit any clear peak. The second important result is the absence of correlation between H/V peak amplitude and the actual site amplification measured on site-to-reference spectral ratios. There are, however, two statistically significant results about the amplitude of the H/V curve: the peak amplitude may be considered as a lower bound estimate of the actual amplification indicated by SSR (it is smaller for 79% of the 104 investigated sites), and, from another point of view, the difference in amplitude exhibits a questioning correlation with the geometrical characteristics of the sediment/basement interface: large SSR/HV differences might thus help to detect the existence of significant 2D or 3D effects.

STOCHASTIC RESONANCE IN HAIR CELL MECHANOELECTRICAL TRANSDUCTION

Hair cells are the mechanoelectrical transducers in the auditory system of many species, including humans. Experiments show that transduction in individual hair cells displays stochastic resonance, with optimum response at the natural noise level of living cells. We find that many of the observed features are captured by a simple version of a physiologically faithful model of the transduction mechanism. These findings may resolve a longstanding puzzle in evolutionary biology concerning the structure of the cochlea.

Noise and stochastic resonance in voltage-gated ion channels.

Using Monte Carlo techniques, I calculate the effects of internally generated noise on information transfer through the passage of action potential spikes along unmyelinated axons in a simple nervous system. I take the Hodgkin-Huxley (HH) description of Na and K channels in squid giant axons as the basis of the calculations and find that most signal transmission noise is generated by fluctuations in the channel open and closed populations. To bring the model closer to conventional descriptions in terms of thermal noise energy, kT, and to determine gating currents, I express the HH equations in the form of simple relations from statistical mechanics where the states are separated by a Gibbs energy that is modified by the action of the transmembrane potential on dipole moments held by the domains. Using the HH equations, I find that the output response (in the probability of action potential spikes) from small input potential pulses across the cell membrane is increased by added noise but falls off when the input noise becomes large, as in stochastic resonance models. That output noise response is sharply reduced by a small increase in the membrane polarization potential or a moderate increase in the channel densities. Because any reduction of noise incurs metabolic and developmental costs to an animal, the natural noise level is probably optimal and any increase in noise is likely to be harmful. Although these results are specific to signal transmission in unmyelinated axons, I suggest that the conclusions are likely to be general.

Ionospheric mapping using satellite data of natural HF noise

Natural HF noise measured by the radiospectrometer IRS-1 aboard satellite InterKosmos-19 was used for ionospheric mapping. The topside sounder aboard the satellite KOSMOS-18o9 could also be used to the same end because its AGC voltage corresponds to the natural noise level near the satellite. From the cut-off frequency of the noise spectrum can the distribution of the local plasma density be derived. Global maps could be deduced that can be helpful when modelling the ionosphere.

Modulation intracavity laser spectroscopy, polarimetry, and interferometry

A review is given of the history of the method of modulation intracavity measurements in which use is made of amplification of a signal in a laser at the frequency of its relaxation oscillations. An analysis is made of the advantages and ultimate potentialities of the method in spectroscopy, polarimetry, and interferometry. The results are reported of an investigation of the laser noise as the principal factor which limits the sensitivity of such measurements. A description is given of the method for stabilization of a cw YAG:Nd3+ laser in which the amplitude noise at frequencies 10–100 kHz is reduced to the natural noise level. It is described how this laser can be used in measurements of the Kerr constants of gases with a birefringence sensitivity at a level of 10−9 rad; the results are given of such measurements carried out on N2, O2, CO2, and H2 at the wavelength of 1.06 μ.

New concepts in biological evaluation of novel protein foods.

AbstractTechnology has advanced to where it is now possible to fabricate new foods having high acceptability and providing better nutrient balance than the traditional foods they replace. If such products ultimately represent a major portion of the diet, then a new approach to toxicology and nutritional evaluation has to evolve to allow proper estimation of the safety and adequacy of the products. Traditional approaches to these problems are based upon the elucidation of major changes in the test organism, i.e., evaluation of substances of high biological potency. For food analogs, any deleterious effect will probably be at levels just above the natural noise level of the system. To compensate for this, most traditional evaluations of analogs have been made by feeding the test substances at extremely high, nonphysiological levels with the hope that this will reveal any toxic response. With this approach, however, many traditional foods would appear to be inadequate. A better technique may be designed to explore the functional consequences of feeding the test analog over several generations, using stress as a modifier to increase sensitivity of the system. Other sensitive measures such as behavior and resistance to disease should be included. The conceptual basis of this approach was used to test a vegetable protein analog (VPA). The feeding of VPA to animals as a significant part of the diet resulted in no change in the capacity of the animal to grow and reproduce and to function under stress conditions. Preliminary results of feeding this material through three generations also produced no changes in the parameters studies.

Limits to Amplification*

The amplification obtainable in a vacuum tube amplifier is limited by the noise in the circuit. Of the various sources of noise the most fundamental and inevitable is thermal agitation of electricity. Other sources are the influence of ions and of shot effect and flicker effect on the current in vacuum tubes, poor contacts, mechanical vibration, and hum from a.-c. cathode heating. These noises and their effects in limiting amplification are discussed in this paper. Although the natural noise level of an amplifier is exceedingly low, modern amplifiers have reached such a stage of perfection that their noise levels often are practically at the natural limit.

Limits to Amplification

The amplification obtainable in a vacuum tube amplifier is limited by the noise in the circuit. Of the various sources of noise the most fundamental and inevitable is thermal agitation of electricity. Other sources are the influence of ions and of shot effect and flicker effect on the current in vacuum tubes, poor contacts, mechanical vibration, and hum from a-c cathode heating. These noises and their effects in limiting amplification are discussed in this paper. Although the natural noise level of an amplifier is exceedingly low, modern amplifiers have reached such a stage of perfection that their noise levels often are practically at the natural limit.

Limits to amplification

The amplification obtainable in a vacuum tube amplifier is limited by the noise in the circuit. Of the various sources of noise the most fundamental and inevitable is thermal agitation of electricity. Other sources are the influence of ions and of shot effect and flicker effect on the current in vacuum tubes, poor contacts, mechanical vibration, and hum from a-c cathode heating. These noises and their effects in limiting amplification are discussed in this paper. Although the natural noise level of an amplifier is exceedingly low, modern amplifiers have reached such a stage of perfection that their noise levels often are practically at the natural limit.