Characteristics of Low-Frequency Horizontal Noise of Ocean-Bottom Seismic Data

2021 ◽  
Author(s):  
Chao An ◽  
Chen Cai ◽  
Lei Zhou ◽  
Ting Yang
Keyword(s):  
Water Waves ◽  
Noise Source ◽  
Random Noise ◽  
Low Frequency ◽  
Ocean Bottom ◽  
Coherent Noise ◽  
Infragravity Waves ◽  
Low Frequencies ◽  
Bottom Currents ◽  
Ocean Bottom Seismographs

Abstract Horizontal records of ocean-bottom seismographs are usually noisy at low frequencies (< 0.1 Hz). The noise source is believed to be associated with ocean-bottom currents that may tilt the instrument. Currently horizontal records are mainly used to remove the coherent noise in vertical records, and there has been little literature that quantitatively discusses the mechanism and characteristics of low-frequency horizontal noise. In this article, we analyze in situ ocean-bottom measurements by rotating the data horizontally and evaluating the coherency between different channels. Results suggest that the horizontal noise consists of two components, random noise and principle noise whose direction barely changes in time. The amplitude and the direction of the latter are possibly related to the intensity and direction of ocean-bottom currents. Rotating the horizontal records to the direction of the principle noise can largely suppress the principle noise in the orthogonal horizontal channel. In addition, the horizontal noise is incoherent with pressure, indicating that the noise source is not ocean surface water waves (infragravity waves). At some stations in shallow waters (<300 m), horizontal noise around 0.07 Hz is found to be linearly proportional to the temporal derivative of pressure, which is explained by forces of added mass due to infragravity waves.

Frequency Limit for the Pressure Compliance Correction of Ocean-Bottom Seismic Data

2020 ◽  
Vol 91 (2A) ◽  
pp. 967-976 ◽  
Author(s):  
Chao An ◽  
S. Shawn Wei ◽  
Chen Cai ◽  
Han Yue
Keyword(s):  
Water Depth ◽  
Seismic Data ◽  
Water Waves ◽  
Pressure Fluctuations ◽  
Vertical Acceleration ◽  
Ocean Bottom ◽  
Bottom Pressure ◽  
Low Frequencies ◽  
Ocean Bottom Pressure ◽  
Ocean Bottom Seismographs

Abstract Vertical records of ocean-bottom seismographs (OBSs) are usually noisy at low frequencies, and one important noise source is the varying ocean-bottom pressure that results from ocean-surface water waves. The relation between the ocean-bottom pressure and the vertical seafloor motion, called the compliance pressure transfer function (PTF), can be derived using background seismic data. During an earthquake, earthquake signals also generate ocean-bottom pressure fluctuations, and the relation between the ocean-bottom pressure and the vertical seafloor motion is named the seismic PTF in this article. Conventionally, we use the whole pressure records and the compliance PTF to remove the compliance noise; the earthquake-induced pressure and the seismic PTF are ignored, which may distort the original signals. In this article, we analyze the data from 24 OBSs with water depth ranging from 107 to 4462 m. We find that for most stations, the investigated frequency range (0.01–0.2 Hz) can be divided into four bands depending on the water depth. In band (I) of lowest frequencies (<0.11, <0.05, and <0.02  Hz for water depth of 107, 1109, and 2650 m, respectively), the vertical seafloor acceleration is composed mostly of pressure compliance noise, which can be removed using the compliance PTF. The compliance PTF is much smaller than the seismic PTF, so distortion of earthquake signals is negligible. In band (II) of higher frequencies (0.11–0.20, 0.05–0.11, and 0.02–0.05 Hz for water depth of 107, 1109, and 2650 m, respectively), the vertical acceleration and ocean-bottom pressure are largely uncorrelated. In bands (III) and (IV) of even higher frequencies (>0.11 and >0.08  Hz for water depth of 1109 and 2650 m, respectively), the compliance noise is negligible, and the ocean-bottom pressure is mostly caused by the seafloor motion. Thus, the compliance can be safely ignored in frequency band (I).

scholarly journals Factors influencing low-frequency noise reduction in typical Chinese dwelling layouts

2020 ◽  
pp. 146134842094297
Author(s):  
Yang Song ◽  
Jian Kang
Keyword(s):  
Noise Reduction ◽  
Noise Exposure ◽  
Noise Source ◽  
Low Frequency ◽  
Frequency Noise ◽  
Low Frequency Noise ◽  
Low Frequencies ◽  
Factors Influencing ◽  
Polyline Distance

Existing approaches to reducing the low-frequency noise exposure of dwellings are not always sufficient. This study investigated the significance of dwelling layout design for low-frequency noise control. The sound distribution in six typical Chinese dwelling layouts was analysed using in-situ measurements under steady-state noise of various low frequencies. The results showed that among two-bedroom dwelling layouts, the overall average noise reduction varied considerably (6 dB). The noise reduction for room levels (number of rooms sound crosses) 1–2 and 2–3 varies by 5 and 3 dB, respectively, and the noise reduction at door openings varies by 5 dB. A model to approximate the low-frequency noise reduction of a layout was developed using the polyline distance from the noise source and the number of walls the polyline has to cross, which were clearly shown to influence low-frequency noise reduction and seem to be the strongest investigated factors.

A low-noise transistorized seismic amplifier

1964 ◽  
Vol 54 (1) ◽  
pp. 347-368
Author(s):  
Stamatios N. Thanos
Keyword(s):  
High Reliability ◽  
Low Noise ◽  
Ocean Bottom ◽  
Low Frequencies ◽  
Input Noise ◽  
Remote Operation ◽  
Source Impedance ◽  
Ocean Bottom Seismographs ◽  
Equivalent Input Noise ◽  
Remote Calibration

abstract The use of transistors for the amplification of fractional microvolt signals at extremely low frequencies is illustrated in the design of an amplifier developed for use in a lunar seismograph. The amplifier has an equivalent input noise voltage of 0.2 microvolts, p-p, with a source impedance of 2000 ohms and a 3 db bandwidth of 0.035 cps to 22 cps. The nominal input impedance is 1700 ohms. It is completely transistorized and performs satisfactorily over a specified temperature range of −20°C to +100°C. Low power requirements, high reliability, and capability for remote calibration and gain change make this amplifier especially suitable for any field or remote operation under extreme environmental conditions. This amplifier is presently being used in ocean bottom seismographs and magnetic variometers.

scholarly journals Nonlinear low-frequency gravity waves in a water-filled cylindrical vessel subjected to high-frequency excitations

2013 ◽  
Vol 469 (2153) ◽  
pp. 20120536 ◽  
Author(s):  
Chunyan Zhou ◽  
Dajun Wang ◽  
Song Shen ◽  
Jing Tang Xing
Keyword(s):  
Gravity Waves ◽  
High Frequency ◽  
Water Waves ◽  
Large Amplitude ◽  
Low Frequency ◽  
Approximation Model ◽  
Fluid Structure Interactions ◽  
Governing Equations ◽  
Low Frequencies ◽  
Nonlinear Fluid

In the experiments of a water storage cylindrical shell, excited by a horizontal external force of sufficient large amplitude and high frequency, it has been observed that gravity water waves of low frequencies may be generated. This paper intends to investigate this phenomenon in order to reveal its mechanism. Considering nonlinear fluid–structure interactions, we derive the governing equations and the numerical equations describing the dynamics of the system, using a variational principle. Following the developed generalized equations, a four-mode approximation model is proposed with which an experimental case example is studied. Numerical calculation and spectrum analysis demonstrate that an external excitation with sufficient large amplitude and high frequency can produce gravity water waves with lower frequencies. The excitation magnitude and frequencies required for onset of the gravity waves are found based on the model. Transitions between different gravity waves are also revealed through the numerical analysis. The findings developed by this method are validated by available experimental observations.

A Novel Image Denoising Method for Matched Filtering System

2012 ◽  
Vol 263-266 ◽  
pp. 2469-2476
Author(s):  
Xin Xu
Keyword(s):  
Spatial Frequency ◽  
Frequency Spectrum ◽  
Lattice Structure ◽  
Random Noise ◽  
Low Frequency ◽  
Similar Distribution ◽  
Coherent Noise ◽  
Denoising Method ◽  
Image Information ◽  
Spatial Frequency Spectrum

One method is proposed to remove the random noise and low-frequency coherent noise in the images of the optic 4f system, which is based on fusion of multiple spatial frequency spectrum images. The multiple spatial frequency spectrum images of once experiment are captured based on the image copying character from the lattice structure of spatial light modulators, which contains the same useful image information and noise with the similar distribution but different values. The random noise and coherent noise in these images are removed by combining it utilizing image fusion technique, which is similar to cumulative mean in time domain. The theoretical analysis and physical experiment suggests that the method is able to remove random noise and low-frequency coherent noise effectively and reserve the useful image information.

Limits of sensitivity of inertial seismometers with velocity transducers and electronic amplifiers

1990 ◽  
Vol 80 (6A) ◽  
pp. 1725-1752 ◽  
Author(s):  
Mark A. Riedesel ◽  
John A. Orcutt ◽  
Robert D. Moore
Keyword(s):  
Noise Level ◽  
Low Frequency ◽  
Noise Spectrum ◽  
Displacement Transducer ◽  
Ocean Bottom ◽  
Good Resolution ◽  
Low Frequencies ◽  
Amplifier Noise ◽  
Order Of Magnitude ◽  
Ground Noise

Abstract Portable instruments such as ocean bottom seismographs and the PASSCAL recorders often use rugged, portable geophones. The desire to use such sensors for relatively low-frequency work has raised questions about the limits of their sensitivity. The lower and upper frequency limits of performance of seismic sensors are determined by the sensor's mass, period, and Q, and by the amplifiers used with those sensors. We have tested Mark Products 1 Hz, 2 Hz, and 4.5 Hz velocity transducers against Streckeisen seismometers in order to examine the limits of their performance in measuring ground noise, particularly at low frequencies. Among the velocity transducers, only the 1 Hz Mark Products L-4 sensor provided good resolution of the 6-sec microseism peak. For this sensor, the lower limits of sensitivity was at approximately 0.06 Hz, although this depends on the amplifier used and the noise level at a given site. The amplifiers examined included conventional, low power, and commutating auto-zero operational amplifiers. It was found that the noise levels of the amplifiers intersected the ground noise level at frequencies ranging between 0.06 and 0.2 sec, depending on the amplifier and the exact circuit design. Measurements indicated that by modeling the amplifier noise for a given circuit correctly, the performance of an amplifier can be predicted with a high degree of accuracy, obviating the need for actual circuit construction to determine performance in the field. Given the very steep slope of the ground noise spectrum between 0.05 and 0.1 Hz and the rapid fall off in a seismometer's output below its resonant frequency, it would require a lowering of amplifier noise by more than an order of magnitude to be able to resolve ground noise at frequencies lower than 0.05 Hz using relatively small geophones such as the L-4. To resolve ground noise at lower frequencies, it is necessary to use a seismometer with a displacement transducer to sense the mass position, such as Guralp or Streckeisen sensors.

Comparisons of downhole geophones and hydrophones

Geophysics ◽  
1992 ◽  
Vol 57 (6) ◽  
pp. 841-847 ◽  
Author(s):  
Christine E. Krohn ◽  
S. T. Chen
Keyword(s):  
High Frequency ◽  
Background Noise ◽  
Low Frequency ◽  
Measured Signal ◽  
Coherent Noise ◽  
Low Frequencies ◽  
Prototype Tool ◽  
The Difference ◽  
Borehole Seismic ◽  
Seismic Applications

Receiver tests were conducted to compare the responses of downhole geophones and hydrophones. Commercial receiver tools use a maximum of eight geophone levels; however, we use hydrophones because we can record 48 levels simultaneously. For frequencies above 300 Hz, signal‐to‐background‐noise ratios for hydrophones and geophones in a prototype tool were comparable. (This prototype tool is a lightweight, large‐clamping‐force device that can record higher frequencies than commercial geophone tools.) For frequencies below 300 Hz, signal‐to‐noise ratios were greater for the geophones than for the hydrophones. A commercial geophone tool had lower low‐frequency signal‐to‐background‐noise ratios than the prototype tool, but greater than those of the hydrophones. Further analysis was performed to determine why the signal‐to‐background‐noise ratios for geophones were greater than those for hydrophones at low frequencies. The measured signal level for a hydrophone was 2.4 times that for a geophone, compared with a theoretical prediction of 1.8. Thus, the signal levels do not explain the difference in signal‐to‐background‐noise ratios. The low‐frequency background noise was attributed to coherent noise in the form of tube waves, a noise type to which hydrophones are much more susceptible than are geophones. Thus, the low signal‐to‐background‐noise ratios at frequencies below 300 Hz for hydrophones resulted from ambient noise propagating as tube waves in the borehole. The high‐frequency background noise was attributed to random seismic noise in the environment and not to instrument noise. These results show that hydrophones, which do not need to be clamped to the borehole wall, are preferable to geophones for high‐frequency borehole seismic applications using first arrivals. Geophones are preferable to hydrophones for borehole seismic applications using reflector arrivals, because these later‐arriving events are obscured by source‐generated tube waves in hydrophone data. Development of a method to reduce both the source‐generated and ambient tube‐wave noise detected by hydrophones would result in high‐quality borehole seismic data at a greatly reduced cost.

Noise source location and scaling of subsonic upper-surface blowing

2020 ◽  
Vol 19 (3-5) ◽  
pp. 191-206
Author(s):  
Trae L Jennette ◽  
Krish K Ahuja
Keyword(s):  
Strouhal Number ◽  
Noise Source ◽  
Low Frequency ◽  
Directivity Pattern ◽  
Source Location ◽  
Dipole Source ◽  
Frequency Noise ◽  
Noise Sources ◽  
Trailing Edge ◽  
Trailing Edge Noise

This paper deals with the topic of upper surface blowing noise. Using a model-scale rectangular nozzle of an aspect ratio of 10 and a sharp trailing edge, detailed noise contours were acquired with and without a subsonic jet blowing over a flat surface to determine the noise source location as a function of frequency. Additionally, velocity scaling of the upper surface blowing noise was carried out. It was found that the upper surface blowing increases the noise significantly. This is a result of both the trailing edge noise and turbulence downstream of the trailing edge, referred to as wake noise in the paper. It was found that low-frequency noise with a peak Strouhal number of 0.02 originates from the trailing edge whereas the high-frequency noise with the peak in the vicinity of Strouhal number of 0.2 originates near the nozzle exit. Low frequency (low Strouhal number) follows a velocity scaling corresponding to a dipole source where as the high Strouhal numbers as quadrupole sources. The culmination of these two effects is a cardioid-shaped directivity pattern. On the shielded side, the most dominant noise sources were at the trailing edge and in the near wake. The trailing edge mounting geometry also created anomalous acoustic diffraction indicating that not only is the geometry of the edge itself important, but also all geometry near the trailing edge.

scholarly journals Earless toads sense low frequencies but miss the high notes

2017 ◽  
Vol 284 (1864) ◽  
pp. 20171670 ◽  
Author(s):  
Molly C. Womack ◽  
Jakob Christensen-Dalsgaard ◽  
Luis A. Coloma ◽  
Juan C. Chaparro ◽  
Kim L. Hoke
Keyword(s):  
High Frequency ◽  
Species Differences ◽  
Low Frequency ◽  
Auditory Brainstem ◽  
Low Frequencies ◽  
Hearing Sensitivity ◽  
Sensory Pathways ◽  
Airborne Sound ◽  
Vibrational Sensitivity ◽  
Species Specific

Sensory losses or reductions are frequently attributed to relaxed selection. However, anuran species have lost tympanic middle ears many times, despite anurans' use of acoustic communication and the benefit of middle ears for hearing airborne sound. Here we determine whether pre-existing alternative sensory pathways enable anurans lacking tympanic middle ears (termed earless anurans) to hear airborne sound as well as eared species or to better sense vibrations in the environment. We used auditory brainstem recordings to compare hearing and vibrational sensitivity among 10 species (six eared, four earless) within the Neotropical true toad family (Bufonidae). We found that species lacking middle ears are less sensitive to high-frequency sounds, however, low-frequency hearing and vibrational sensitivity are equivalent between eared and earless species. Furthermore, extratympanic hearing sensitivity varies among earless species, highlighting potential species differences in extratympanic hearing mechanisms. We argue that ancestral bufonids may have sufficient extratympanic hearing and vibrational sensitivity such that earless lineages tolerated the loss of high frequency hearing sensitivity by adopting species-specific behavioural strategies to detect conspecifics, predators and prey.

scholarly journals Estimation of the Noise Source Level of a Commercial Ship Using On-Board Pressure Sensors

2021 ◽  
Vol 11 (3) ◽  
pp. 1243
Author(s):  
Hongseok Jeong ◽  
Jeung-Hoon Lee ◽  
Yong-Hyun Kim ◽  
Hanshin Seol
Keyword(s):  
Noise Source ◽  
Pressure Sensors ◽  
Low Frequency ◽  
Frequency Resolution ◽  
Source Strength ◽  
Recording Time ◽  
Source Level ◽  
The One ◽  
Hydrophone Array ◽  
Good Agreement

The dominant underwater noise source of a ship is known to be propeller cavitation. Recently, attempts have been made to quantify the source strength using on-board pressure sensors near the propeller, as this has advantages over conventional noise measurement. In this study, a beamforming method was used to estimate the source strength of a cavitating propeller. The method was validated against a model-scale measurement in a cavitation tunnel, which showed good agreement between the measured and estimated source levels. The method was also applied to a full-scale measurement, in which the source level was measured using an external hydrophone array. The estimated source level using the hull pressure sensors showed good agreement with the measured one above 400 Hz, which shows potential for noise monitoring using on-board sensors. A parametric study was carried out to check the practicality of the method. From the results, it was shown that a sufficient recording time is required to obtain a consistent level at high frequencies. Changing the frequency resolution had little effect on the result, as long as enough data were provided for the one-third octave band conversion. The number of sensors affected the mid- to low-frequency data.

Sign in / Sign up

Export Citation Format

Share Document