High Noise Model Research Articles

Noise and site response characterization in Makassar Strait and Celebes Sea based on Ocean Bottom Seismometer

To overcome the limited information in the northern waters of Sulawesi Island, ocean bottom seismometers (OBS) were installed in the northern part of the Makassar Strait and the Sulawesi Sea. OBS data were analysed using passive seismic methods to determine the characteristics of noise and site response in the Makassar Strait and the Celebes Sea. Probabilistic Power Spectral Density (PPSD) from OBS station showed microtremor in the period 0.06 – 0.7 s, secondary microseismic peak in the period 0.9 – 2 s, secondary microseismic peak in the period 4 – 8 s, and hum in the period more than 10 s. The amplitude of the noise power is in the range of New Low Noise Model (NLNM) and New High Noise Model (NHNM) for a period <10 s and slightly above NHNM for a period >10 s for OBS IGGCAS F-type. For OBS IGGCAS G-type, the noise power amplitude is in the period < 0.7 s in the NLNM and NHNM ranges. However, there is a tendency for the noise power amplitude to be flat with an amplitude above NHNM for a period > 0.7 s. The noise power’s amplitude depends on the station’s location, climate, instruments, daily variations, and seasonal variations. Horizontal-to-Vertical Spectral Ratio (HVSR) in the North Makassar Strait shows an H/V curve with an unclear peak in the middle of the strait and multiple peaks in the eastern part of the strait with a frequency range of 1.35 – 4.7 Hz. Between the Makassar Strait and the Celebes Sea, the H/V curve shows a flat peak and multiple peaks with a frequency range of 1.10 – 4.03 Hz. Meanwhile, in the Celebes Sea, the H/V curve shows an unclear peak (unclear peak) and several peaks (multiple peaks) with a frequency range of 0.65 – 6.25 Hz.

Analysis of Regional Ambient Seismic Noise in the Chukchi Sea Area in the Arctic Based on OBS Data from the Ninth Chinese National Arctic Scientific Survey

Ambient noise plays a crucial role in influencing the observation quality at seismic stations. By studying the distribution patterns of ambient noise, we can gain initial insights into the noise conditions within a specific research area. This paper investigates the properties of ambient noise in different frequency bands under environmental settings in the Chukchi Sea region, utilizing data collected from ocean bottom seismometers (OBSs) deployed during the Ninth Chinese National Arctic Scientific Survey. The probability density function (PDF) method is used to reveal the distinctive features of ambient noise. In addition, by comparing the crowed number values of ambient noise in the Chukchi Sea area with the global new low-noise model (NLNM) and new high-noise model (NHNM), a more comprehensive understanding of the patterns, distribution characteristics, and sources of ambient noise in the Arctic Chukchi Sea area is gained. The study suggests that the overlying sea ice in the Arctic Chukchi Sea area can suppress the microseismic band ambient noise, and the overall level of ambient noise in the Chukchi Sea area lies between the land seismic ambient noise level and the ambient noise level in the middle- and low-latitude sea areas. Meanwhile, an abnormal power spectrum caused by different levels of natural earthquakes is observed. This study fills the gap by using seafloor seismic instruments to investigate ambient noise in the Chukchi Sea area.

A broadband seismological observatory at Larsemann Hills, Antarctica: Noise characteristics and data quality

Antarctica, the southernmost ice-covered continent, plays a pivotal role in unraveling Earth's intricate evolutionary processes. Several studies have been conducted to comprehend the crustal structure of West Antarctica. However, our understanding of the sub-surface structure in the East Antarctica region, particularly along Princess Elizabeth Land (PEL), remains limited due to the scarcity of geophysical data. To bridge this knowledge gap, we (NCESS) established a permanent broadband seismological observatory in the captivating region of Larsemann Hills, East Antarctica. In addition, we investigate the noise characteristics at the station, employing power spectral density (PSD) measurements. Results have been promising, indicating that the noise levels are within the range of New High Noise Model and New Low Noise Model. Monthly variations in PSD reveal different noise levels throughout the year, with winter months exhibiting lower levels of microseismic noise attributed to lower temperatures and frozen sea surfaces. The long-period noise is higher in April & May, possibly due to high-speed winds and lower in September & October. The outcomes serve as a testament to the success of our installation and ensure a valuable data set. The data will contribute to a comprehensive investigation of sub-surface structures in the PEL region of East Antarctica, enhancing our understanding of geological processes and tectonic evolution. Furthermore, the findings will serve as a valuable resource for future research and contribute to our knowledge of Earth's dynamic processes.

Infrasound and Low-Audible Acoustic Detections from a Long-Term Microphone Array Deployment in Oklahoma

A three-microphone acoustic array (OSU1), with microphones that have a flat response from 0.1 to 200 Hz, was deployed for 6 years (2016–2022) at Oklahoma State University (OSU) in Stillwater, Oklahoma, and sampled at 1000 Hz. This study presents a new dataset of acoustic measurements in a high interest region (e.g., study of tornado infrasound), provides a broad overview of acoustic detections and the means to identify them, and provides access to these recordings to the broader scientific community. A wide variety of infrasound and low-audible sources were identified and characterized via analysis of time traces, power spectral densities, spectrograms, and beamforming. Low, median, and high noise models were compared with global noise models. Detected sources investigated include natural (microbaroms, bolides, earthquakes, and tornadoes) and anthropomorphic (fireworks, airplanes, and munition detonations) phenomena. Microbarom detections showed consistency with literature (~0.2 Hz with peak amplitude in the winter) and evidence that the frequency was inversely related to the amplitude. Fireworks and airplanes served as verified local events for the evaluation of data quality and processing procedures. Infrasound from munition detonations, that occur nearly daily at a location 180 km southeast of OSU1, matched the available ground truth on days with favorable propagation to OSU1. A clear bolide detection with an estimated position of approximately 300 km from OSU1 was shown. Most detected earthquakes were seismic arrivals due to sensor vibrations; however, the largest earthquake in Oklahoma history showed an acoustic arrival. Finally, data from multiple tornadoes are discussed, including a previously unpublished quasi-linear convective system tornado.

Seismic Noise Analysis in InaTEWS Earthquake Station Network (Case Study: Flores Earthquake 7.4, 14 December 2021)

Meteorological, Climatology and Geophysics Agency (BMKG) is the agency responsible for providing information on earthquake parameters in Indonesia. BMKG has installed 411 seismometers network spread across Indonesia, this network is known as the Indonesia Tsunami Early Warning System (InaTEWS) network. The dense distribution of the seismometer is expected to be able to provide accurate earthquake parameter results. However, the accuracy of earthquake parameters does not only depend on many stations but also on the quality of the data recorded by the seismometer. In this study, an analysis of 15 data quality was carried out at the nearest station that recorded the Flores earthquake on December 14, 2021. Analysis of data quality using the power spectral density (PSD) and probability density functions (PDFs) methods, where good data quality can be seen in the spectrum of the seismograph recordings that are between the Peterson’s new high noise model (NHNM) and new low noise model (NLNM).

Ambient Infrasound Noise, Station Performance, and Their Relation to Land Cover across Alaska

AbstractThe addition of 108 infrasound sensors—a legacy of the temporary USArray Transportable Array (TA) deployment—to the Alaska regional network provides an unprecedented opportunity to quantify the effects of a diverse set of site conditions on ambient infrasound noise levels. TA station locations were not chosen to optimize infrasound performance, and consequently span a dramatic range of land cover types, from temperate rain forest to exposed tundra. In this study, we compute power spectral densities for 2020 data and compile new ambient infrasound low- and high-noise models for the region. In addition, we compare time series of root-mean-squared (rms) amplitudes with wind data and high-resolution land cover data to derive noise–wind speed relationships for several land cover categories. We observe that noise levels for the network are dominated by wind, and that network noise is generally higher in the winter months when storms are more frequent and the microbarom is more pronounced. Wind direction also exerts control on noise levels, likely as a result of infrasound ports being systematically located on the east side of the station huts. We find that rms amplitudes correlate with site land cover type, and that knowledge of both land cover type and wind speed can help predict infrasound noise levels. Our results show that land cover data can be used to inform infrasound station site selection, and that wind–noise models that incorporate station land cover type are useful tools for understanding general station noise performance.

Correcting the Background Tilt Signal of the Horizontal Seismometer Using a Rotation Sensor

Abstract In observational seismology, the long-period background noise level in horizontal seismometer components is always higher than the vertical component at the same location. It is believed that the horizontal long-period noise is mostly attributed to ground tilt, yet the authentic tilt recordings of background noise in the seismic frequency band (0.01–20 Hz) have not been recorded successfully. We demonstrate the use of a newly developed optical-based rotation sensor, blueSeis-3A, to correct for the tilt effect in a horizontal seismometer. A station with a horizontal long-period (1 &amp;lt; T &amp;lt; 100 s) background noise level higher than the global new high-noise model was chosen, where a seismometer, a tiltmeter, and a rotation sensor were collocated. We first confirmed that the horizontal recordings from a tiltmeter and a seismometer were visually consistent, although it was unclear if tilt contamination existed in both recordings. It became evident until the ground tilt recorded by a rotation sensor was found to be waveform-matched with them, indicating that both sensors were contaminated by tilt. The spectrum of tilt records showed that ground tilts were mostly at period bands &amp;gt;1 s. By subtracting tilt from seismometer records, the horizontal background noise levels could be improved, approximately to the resolution level of the rotation sensors. Our results demonstrate that collocating rotation sensors with seismometers is a feasible way to improve the quality of the long-period background noise level in seismometer horizontal components when rotation sensors are sufficiently sensitive.

Design of low frequency fiber optic Fabry–Perot seismometer based on transfer function analysis

We develop a low frequency fiber Fabry–Perot (F-P) seismometer based on transfer function analysis. The seismometer structure and demodulation system accuracy are limitations of low frequency seismic monitoring. The transfer function of the F-P seismometer is analyzed, and the mass displacement spectrum (MDS) is introduced. MDS provides guidance for mechanical structure design and optical interferometer analysis to achieve low noise. The F-P seismometer prototype is built. The experiment shows that the prototype has an average noise of 6.74 ng/√ Hz below 50 Hz, and its noise is less than that of the global new high noise model within 0.16–50 Hz, whose potential is considerable.

Establishing High-Frequency Noise Baselines to 100 Hz Based on Millions of Power Spectra from IRIS MUSTANG

ABSTRACTAdvances in seismic instrumentation have enabled data to be recorded at increasing sample rates. This has in turn created a need to establish higher frequency baselines for assessing data quality, as the widely used new high-noise model (NHNM) and new low-noise model (NLNM) of Peterson (1993) do not extend to frequencies above 10 Hz. To provide a baseline for higher frequencies (10–100 Hz), we examine power spectral density probability density functions (PSDPDFs) for high-sample rate stations available from the Incorporated Research Institutions for Seismology Data Services Modular Utility for STAtistical kNowledge Gathering (IRIS MUSTANG) quality control system. We compute high-frequency high- and low-noise baselines by matching the appropriate composite PSDPDF percentile points to NHNM and NLNM power levels at overlapping frequencies (1–10 Hz) and then extending to higher frequencies (10–100 Hz) with piecewise linear fits to the matching PSDPDF percentile.We find that the Peterson NLNM remains an accurate representation of the lower bound of global ambient Earth noise because it is lower than 99.9% of Global Seismographic Network power spectral densities. We present high-frequency high- and low-noise baselines intended primarily for use by temporary networks targeting high-frequency signals (e.g., monitoring of aftershocks or induced seismicity) based on statistics of PSDPDFs from all publicly available high-sample rate data.Most publicly available high-sample rate data are recorded by temporary deployments, and the experiment design and scientific targets of these deployments strongly influence the observed statistical distribution of high-frequency noise. We anticipate that the noise baselines presented here will be useful in automated quality control of high-sample rate seismic data. However, we note that establishing a low-noise model that accurately represents the lowest possible ambient Earth noise at frequencies up to 100 Hz will require additional continuous high-sample rate data from high-quality permanent stations in low-noise environments.

Robust UKF-IMM Filter for Tracking an Off-road Ground Target

In this paper, the design of a robust UKF-IMM filter for tracking a fulltime off-road ground target is studied and carried out. A detailed description of the target dynamic systems with respect to motion modelling is done for a sharply maneuvering target. A four model IMM filter with two discrete white noise acceleration models and two horizontal coordinated turn models is proposed. In this IMM filter, a low noise and high noise model is proposed for the two pairs of motion models. Low noise model for non-maneuvering or slow maneuvering situations and high noise model for quick and sharp maneuvering situations. The Unscented Kalman filter is used as the base filter due to the highly nonlinear horizontal coordinated turn model with unknown turn rates along with linear Kalman filter for linear systems. Simulation is carried out and results are presented showing the performance of the proposed estimator and demonstrates its capability to perform its designed purpose. The simulated results show that the four model IMM filter can track the highly maneuvering off-road target with acceptable error margin. The error dynamics are observed to be stable with good maneuver detection characteristics. The proposed filter has a low computation complexity and therefore can be adapted to most computers.

Broadband FBG resonator seismometer: principle, key technique, self-noise, and seismic response analysis.

A broadband optical fiber seismometer based on FBG resonator is proposed for earthquake monitoring. The principle and key technique, high-resolution ultralow-frequency wavelength interrogation by dual-laser swept frequency and beat frequency method, are discussed and analyzed. From the simulation and test results, the seismometer works at broadband range from 0.01 Hz to 10 Hz with a sensitivity of better than 330 pm/g and the wavelength resolution of the interrogation system is better than 0.001 pm/√Hz from 0.1 Hz to 10 Hz. A three-channel correlation method is used to measure the self-noise of the seismometer. It reaches a noise level of 2.7 × 10-7 ms-2/√Hz@0.1 Hz, which is lower than the earth's background noise (the new high noise model, NHNM). An earthquake monitoring experiment is conducted in a low noise seismic station. The recorded seismic waves are analyzed, which suggests that the proposed seismometer has the ability to record the close microearthquake and distant great earthquake with a high signal-noise ratio (SNR). This is the first time that a FBG-based middle-long period seismometer with lower self-noise than NHNM and large dynamic range (100 dB) is reported.

Microtremor Response of a Mass Movement in Federal District of Brazil

The present study provides a brief description of the ambient noise recorded at a slow moving mass movement in Ribeirao Contagem Basin. The area is an interesting natural laboratory as river detachment processes in a number of diferent stages can be identiied and are easily accessible. We investigate the site dynamic characteristics of the study area by recording ambient noise time-series at nine points, using portable nine three-component short period seismometers. The time-series are processed to give both horizontal to vertical spectral ratio (HVSR) curves as well as time-frequency plots of noise power spectral density (SPD). The HVSR curves illustrate and quantify aspects of site resonance efects due to the local geological setting. Probability density function (PDF) shows that noise level lies well between new high noise model (NHNM) and new lower noise model (NLNM) and their probabilities are higher above 2 Hz. HVSR curves present a uniform lithologically controlled peak at 2 Hz. Directional properties of the waveield are determined by beamforming method. The f-k analysis results in the E-W component show that at 5 Hz phase velocities are close to 1700 m/s while at 10 Hz dropped to 250 m/s. We observed that between 5 and 16 Hz the incoming waveield arrive from 260 degrees. Further studies will apply a detailed noise analysis for relating the dynamics of the landslide (which can be retriggered by river erosion as well as rainfalls and seismic shaking) to possible changes in detectable physical properties.

New comprehensive standard seismic noise models and 3D seismic noise variation for Morocco territory, North Africa, obtained using seismic broadband stations

In the current work, we constructed new comprehensive standard seismic noise models and 3D temporal-spatial seismic noise level cubes for Morocco in north-west Africa to be used for seismological and engineering purposes. Indeed, the original global standard seismic noise models published by Peterson (1993) and their following updates by Astiz and Creager (1995), Ekström (2001) and Berger et al. (2003) had no contributing seismic stations deployed in North Africa. Consequently, this preliminary study was conducted to shed light on seismic noise levels specific to north-west Africa. For this purpose, 23 broadband seismic stations recently installed in different structural domains throughout Morocco are used to study the nature and characteristics of seismic noise and to create seismic noise models for Morocco. Continuous data recorded during 2009, 2010 and 2011 were processed and analysed to construct these new noise models and 3D noise levels from all stations. We compared the Peterson new high-noise model (NHNM) and low-noise model (NLNM) with the Moroccan high-noise model (MHNM) and low-noise model (MLNM). These new noise models are comparable to the United States Geological Survey (USGS) models in the short period band; however, in the period range 1.2 s to 1000 s for MLNM and 10 s to 1000 s for MHNM display significant variations. This variation is attributed to differences in the nature of seismic noise sources that dominate Morocco in these period bands. The results of this study have a new perception about permanent seismic noise models for this spectacular region and can be considered a significant contribution because it supplements the Peterson models and can also be used to site future permanent seismic stations in Morocco.

Evaluation of performance of z-component of Nigerian seismographic stations from spectral analysis

Preliminary noise analysis has been carried out on the Z-components of the Nigerian National Network of Seismographic Stations (NNNSS) using data collected from the five operational stations (Toro, Kaduna, Nsukka, Awka and Ife) in 2012. The results of the analysis from noise spectra using SEISAN software clearly showed that the noise levels at the respective stations are high and the average noise levels are above the high noise model of Peterson curves. The possible sources of noise are cultural, actual earth vibrations and instrumentation. The study is intended to quantify the amount of noise present in the existing NNNSS and compare with Peterson noise curves, and understand the noise characteristics in order to adopt better practices in the day-to-day seismic stations’ operations in Nigeria. Key words: National network of seismographic stations (NNNSS), noise, spectral analysis, signal to noise ratio.

Nonlocal Hierarchical Dictionary Learning Using Wavelets for Image Denoising

Exploiting the sparsity within representation models for images is critical for image denoising. The best currently available denoising methods take advantage of the sparsity from image self-similarity, pre-learned, and fixed representations. Most of these methods, however, still have difficulties in tackling high noise levels or noise models other than Gaussian. In this paper, the multiresolution structure and sparsity of wavelets are employed by nonlocal dictionary learning in each decomposition level of the wavelets. Experimental results show that our proposed method outperforms two state-of-the-art image denoising algorithms on higher noise levels. Furthermore, our approach is more adaptive to the less extensively researched uniform noise.

New Step for Broadband Seismic Observation on the Seafloor: BBOBS-NX

Essential information for clarifying geodynamic processes is obtained by imaging the Earth's interior through geophysical observations. Huge oceanic areas are important locations for conducting such observations. The broadband ocean-bottom seismometer (BBOBS) that we developed has been used since 1999 in several array observations, which gave us new information. But, the BBOBS's noise model in periods longer than 10 s indicates the high noise level in horizontal components above the new high noise model (NHNM), although the vertical one is between the NHNM and the new low noise model (NLNM). It makes it difficult to apply modern analysis methods using horizontal component waveforms even from the data of the one-year-long observation at a single station. Recently, we have developed a geophysical instrument to investigate the oceanic mantle, namely the next-generation broadband ocean-bottom seismometer (BBOBS-NX), operated by a remotely operated underwater vehicle (ROV). The BBOBS-NX provides data of much higher quality than the conventional BBOBS, because it shows a comparable noise model in horizontal components with that of land seismic stations in periods longer than 10 s. Comparison between bottom currents and horizontal particle motions of the BBOBS-NX and conventional BBOBSs clearly indicates the effective reduction of the noise due to the bottom current in this period range. A preliminary receiver function analysis also shows the advantage of the BBOBS-NX to the conventional BBOBS, even if the observation period of the former was shorter than a quarter of that of the latter.

A High- and Low-Noise Model for High-Quality Strong-Motion Accelerometer Stations

We present reference noise models for high-quality strong-motion accelerometer installations. We use continuous accelerometer data to derive very broadband (50 Hz–100 s) high- and low-noise models. The proposed noise models are compared (1) to the broadband seismometer Peterson (1993) noise models; (2) the datalogger self-noise and background noise levels at existing Swiss and Southern California strong-motion stations; and (3) typical earthquake signals recorded in Switzerland and worldwide. The accelerometer low-noise model (ALNM) is dominated by instrument noise from the sensor and datalogger. The accelerometer high-noise model (AHNM) reflects (1) at high frequencies the acceptable site noise in urban areas, (2) at mid-periods the microseismal peaks and (3) at long periods the maximum noise observed from well-insulated sensor/datalogger systems placed in vault quality sites. This study also provides confirmation of the remarkable capability of modern strong-motion accelerometers to record low-amplitude ground motions with seismic observation quality over a broad frequency range.

New Seismic Noise Models Obtained Using Very Broadband Stations

It has been two decades since the last comprehensive standard model of ambient earth noise was published Peterson (Observations and modelling of seismic background noise, US Geological Survey, open-file report 93–322, 1993). The PETERSON model was updated by analyzing the absolute quietest conditions for stations within the GSN (Berger et al. in J Geophys Res 109, 2005; Mcnamara and Buland in Bull Seism Soc Am 94:1517–1527, 2004; Ringler et al. in Seismol Res Lett 81(4) doi: 10.1785/gssrl.81.4.605 , 2010). Unfortunately, both the original model and the updated models did not include any deployed station in North Africa and Middle East, which reflects the noise levels within the desert environment of those regions. In this study, a survey was conducted to create a new seismic noise model from very broadband stations which recently deployed in North Africa. For this purpose, 1 year of continuous recording of seismic noise data of the Egyptian National Seismic Network (ENSN) was analyzed in order to create a new noise model. Seasonal and diurnal variations in noise spectra were recorded at each station. Moreover, we constructed a new noise model for each individual station. Finally, we obtained a new cumulative noise model for all the stations. We compared the new high-noise model (EHNM) and new low-noise model (ELNM) with both the high-noise model (NHNM) and low-noise model (NLNM) of Peterson (Observations and modelling of seismic background noise, US Geological Survey, open-file report 93–322, 1993). The obtained noise levels are considerably lower than low-noise model of Peterson (Observations and modelling of seismic background noise, US Geological Survey, open-file report 93–322, 1993) at ultra long period band (ULP band), but they are still below the high-noise model of Peterson (Observations and modelling of seismic background noise, US Geological Survey, open-file report 93–322, 1993). The results of this study could be considered as a first step to create permanent seismic noise models for North Africa and Middle East regions.

The IDC Seismic, Hydroacoustic and Infrasound Global Low and High Noise Models

The International Data Centre (IDC) in Vienna, Austria, is determining, as part of automatic processing, sensor noise levels for all seismic, hydroacoustic, and infrasound (SHI) stations in the International Monitoring System (IMS) operated by the Provisional Technical Secretariat of the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO). Sensor noise is being determined several times per day as a power spectral density (PSD) using the Welch overlapping method. Based on accumulated PSD statistics a probability density function (PDF) is also determined, from which low and high noise curves for each sensor are extracted. Global low and high noise curves as a function of frequency for each of the SHI technologies are determined as the minimum and maximum of the individual station low and high noise curves, respectively, taken over the entire network of contributing stations. An attempt is made to ensure that only correctly calibrated station data contributes to the global noise models by additionally considering various automatic detection statistics. In this paper global low and high noise curves for 2010 are presented for each of the SHI monitoring technologies. Except for a very slight deviation at the microseism peak, the seismic global low noise model returns identically the Peterson (1993) NLNM low noise curve. The global infrasonic low noise model is found to agree with that of Bowman et al. (2005, 2007) but disagrees with the revised results presented in Bowman et al. (2009) by a factor of 2 in the calculation of the PSD. The global hydroacoustic low and high noise curves are found to be in quantitative agreement with Urick’s oceanic ambient noise curves for light to heavy shipping. Whale noise is found to be a feature of the hydroacoustic high noise curves at around 15 and 25 Hz.

Very broadband seismic background noise analysis of permanent good vaulted seismic stations

This paper describes the results of a preliminary study conducted to analyze seismic background noise at sites of recently deployed very broadband stations of the Egyptian National Seismological Network (ENSN). The main purpose of the study is to assess the effects of permanent seismic vault construction and also to establish characteristics and origin of seismic noise at those sites. Another goal of this study is to determine the time needed for noise at those sites to stabilize. The power spectral densities of background noise at short period band (SP), very broadband (VBB), and ultra long period band (ULP) for each component of each broadband seismometer deployed in the different investigated sites are calculated. A MATLAB code has been developed that manages data processing and data analysis and compares the results with the high-noise model (NHNM) and low-noise model (NLNM) of Peterson (1993). Based on the obtained analysis, the noise stability and the efficiency of each station to record regional and teleseismic events are measured. The results of this study could be used in the future to evaluate station quality, to improve those processes that require background noise values, such as automatic association, and to improve the estimation of station and network detection and location thresholds.