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

2013 ◽  
Vol 29 (1) ◽  
pp. 85-102 ◽  
Author(s):  
Carlo Cauzzi ◽  
John Clinton
Keyword(s):  
Urban Areas ◽  
Strong Motion ◽  
Low Noise ◽  
Noise Model ◽  
Accelerometer Data ◽  
High Quality ◽  
Broadband Seismometer ◽  
Instrument Noise ◽  
Low Amplitude ◽  
Noise Models

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.

scholarly journals Instrument self-noise and sensor misalignment

2013 ◽  
Vol 36 ◽  
pp. 17-20 ◽  
Author(s):  
A. Gerner ◽  
G. Bokelmann
Keyword(s):  
The Self ◽  
Noise Model ◽  
Analysis Method ◽  
Broadband Seismometer ◽  
Real Self ◽  
Noise Models

Abstract. In this study we investigate self-noise of RefTekTM 151-60A "Observer" broadband seismometers (flat to velocity between 50 Hz down to T0=60 s, f0≈17 mHz) using the coherency analysis method introduced by Sleeman et al. (2006). We present a self-noise model for this type of sensor and compare it to the self-noise models of the standard observatory sensor STS-2 (Streckeisen) and RefTek's 151-120 broadband seismometer, which both have natural periods T0 of 120 s. We further report on the sensitivity of this technique to sensor misalignment and our success of eliminating leakage of the omnipresent microseism noise into self-noise estimates by numerically rotating seismic traces in order to find real self-noise.

scholarly journals Noise Characterization in InAlAs/InGaAs/InP pHEMTs for Low Noise Applications

2017 ◽  
Vol 7 (1) ◽  
pp. 176
Author(s):  
Z. A. Djennati ◽  
K. Ghaffour
Keyword(s):  
Noise Figure ◽  
High Electron Mobility Transistor ◽  
Low Noise ◽  
Noise Model ◽  
Good Prediction ◽  
High Electron ◽  
Source Impedance ◽  
Noise Amplifier ◽  
Noise Characterization ◽  
Noise Models

In this paper, a noise revision of an InAlAs/InGaAs/InP psoeudomorphic high electron mobility transistor (pHEMT) in presented. The noise performances of the device were predicted over a range of frequencies from 1GHz to 100GHz. The minimum noise figure (NFmin), the noise resistance (Rn) and optimum source impedance (Zopt) were extracted using two approaches. A physical model that includes diffusion noise and G-R noise models and an analytical model based on an improved PRC noise model that considers the feedback capacitance Cgd. The two approaches presented matched results allowing a good prediction of the noise behaviour. The pHEMT was used to design a single stage S-band low noise amplifier (LNA). The LNA demonstrated a gain of 12.6dB with a return loss coefficient of 2.6dB at the input and greater than -7dB in the output and an overall noise figure less than 1dB.

Challenges and Perspectives for Lowering the Vertical-Component Long-Period Detection Level

2021 ◽  
Author(s):  
Thomas Forbriger ◽  
Walter Zürn ◽  
Rudolf Widmer-Schnidrig
Keyword(s):  
Normal Mode ◽  
Atmospheric Correction ◽  
Detection Threshold ◽  
Vertical Component ◽  
Low Noise ◽  
Detection Sensitivity ◽  
Noise Model ◽  
Detection Level ◽  
Broadband Seismometer ◽  
First Case

Abstract For observations of vertical-component acceleration in the normal-mode band (0.3–10 mHz), the detection sensitivity for signals from the Earth’s body can be improved to levels below the Peterson low-noise model (PLNM). This is achieved by deterministic procedures that (at least partly) remove the accelerations originating from atmospheric mass fluctuations. The physical models used in such corrections are still too simple and fail at frequencies above 3 mHz. Anticipating improved atmospheric correction procedures, we explore the prospects of lowering the detection level. From recordings of excellent vertical-component sensors operated under exceptional site conditions at the Black Forest Observatory, we select time windows of very low background signal, for which all of the contributing broadband seismometers showed their best performance. Streckeisen seismometers of type STS-1, STS-2, and STS-6A, a Nanometrics Trillium T360, and the superconducting gravimeter (SG) SG056 manufactured by GWR Instruments take part in this comparison. Because of their low level of self-noise, the STS-1 and the SG056-G1 benefit the most from a correction with the best currently available improved Bouguer plate model for atmospherically induced signals at frequencies below 1 mHz. As far as we know, this is the first case in which the background level of a broadband seismometer could be lowered below the PLNM. At signal periods beyond the normal-mode band (investigated up to 12 hr), the gravimeters show the lowest level of self-noise, directly followed by the STS-6A. In the band from 0.3 to 10 mHz, the STS-1 has the lowest level of self-noise, which is at least 4 dB below the PLNM, directly followed by the T360 and the STS-6A. Sensors of lower self-noise than the currently manufactured STS-6A or T360 are needed before improved atmospheric correction procedures lead to a significantly lower vertical-component detection threshold.

Frequency limits for seismometers as determined from signal-to-noise ratios. Part 2. The feedback seismometer

1992 ◽  
Vol 82 (2) ◽  
pp. 1099-1123
Author(s):  
Peter W. Rodgers
Keyword(s):  
Seismic Noise ◽  
Transfer Functions ◽  
Low Noise ◽  
Noise Model ◽  
Power Density Spectrum ◽  
Signal To Noise ◽  
Density Spectrum ◽  
Velocity Feedback ◽  
Noise Models ◽  
Feedback Seismometer

Abstract The range of frequencies that a seismometer can record is nominally set by the corner frequencies of its amplitude frequency response. In recording pre-event noise in very quiet seismic sites, the internally generated self-noise of the seismometer can put further limits on the range of frequencies that can be recorded. Some examples of such low seismic noise sites are Lajitas, Texas; Deep Springs, California; and Karkaralinsk, U.S.S.R. In such sites, the seismometer self-noise can be large enough to degrade the signal-to-noise ratio (SNR) of the recorded pre-event data. The widely used low seismic noise model (LNM) (due to Peterson, 1982; Peterson and Hutt, 1982; Peterson and Tilgner, 1985; Peterson and Hutt, 1989) is used as representative of the input ground motion acceleration power density spectrum (pds) at such very low noise sites. This study determines the range of frequencies for which the SNR of a feedback seismometer exceeds 3 db (a factor of 2 in power and 1.414 in amplitude). Analytic expressions for the SNR are developed for three types of feedback seismometers. These are the displacement feedback, velocity feedback, and coil-to-coil velocity feedback seismometers. It was found that the analytic SNRs of the displacement and velocity feedback seismometers are identical and that the SNRs for the coil-coil feedback seismometer and the electromagnetic seismometer are also the same. The signal pds using Peterson's LNM as an input is developed for each of the three types of feedback seismometers. Suspension noise is modeled following Aki and Richards (1980). In order to model the electronically caused component of the self-noise, the electronic noise properties of two commonly used operational amplifiers (Precision Monolithics OP-27 and the Burr-Brown OPA2111 FET) are described. Using these, noise models are developed for a synchronous demodulator and a chopper-stabilized amplifier. These noise models are used to numerically compute the SNRs for the two feedback seismometers used as examples, which are the Guralp Systems CMG-3ESP and Sprengnether Instruments SBX-1000 feedback seismometers. For each of the example seismometers, the calculated range of frequencies for which their SNR exceeds 3 db is as follows: the CMG-3ESP, 0.025 to 13.3 Hz; the SBX-1000, 0.098 to 11.3 Hz. The calculated and measured SNRs for the CMG-3ESP are compared. The calculated upper frequency for a SNR of 3 db was 13.3 Hz compared with 18.4 Hz measured in the noise tests. The calculated lower frequency for a SNR of 3 db was 0.025 Hz, whereas the measured value was 0.047 Hz. The difference is most likely due to the fact the CMG-3ESP is cut off at 0.1 Hz. Formulas are developed in Appendix A for calculating the SNR and self-noise of identical, colocated seismometers from their recorded outputs. The analytic transfer functions, midband gain, upper and lower corner frequencies, and bandwidths for the three types of feedback seismometers are given in Appendix B for comparison with the frequency limits set by the SNR.

scholarly journals Noise and Breakdown Characterization of SPAD Detectors with Time-Gated Photon-Counting Operation

Sensors ◽  
2021 ◽  
Vol 21 (16) ◽  
pp. 5287
Author(s):  
Hiwa Mahmoudi ◽  
Michael Hofbauer ◽  
Bernhard Goll ◽  
Horst Zimmermann
Keyword(s):  
Breakdown Voltage ◽  
Single Photon ◽  
Photon Counting ◽  
Low Noise ◽  
Dark Count ◽  
Fully Integrated ◽  
Trade Offs ◽  
And Performance ◽  
Noise Models

Being ready-to-detect over a certain portion of time makes the time-gated single-photon avalanche diode (SPAD) an attractive candidate for low-noise photon-counting applications. A careful SPAD noise and performance characterization, however, is critical to avoid time-consuming experimental optimization and redesign iterations for such applications. Here, we present an extensive empirical study of the breakdown voltage, as well as the dark-count and afterpulsing noise mechanisms for a fully integrated time-gated SPAD detector in 0.35-μm CMOS based on experimental data acquired in a dark condition. An “effective” SPAD breakdown voltage is introduced to enable efficient characterization and modeling of the dark-count and afterpulsing probabilities with respect to the excess bias voltage and the gating duration time. The presented breakdown and noise models will allow for accurate modeling and optimization of SPAD-based detector designs, where the SPAD noise can impose severe trade-offs with speed and sensitivity as is shown via an example.

TREMOR: A Wireless MEMS Accelerograph for Dense Arrays

2005 ◽  
Vol 21 (1) ◽  
pp. 91-124 ◽  
Author(s):  
John R. Evans ◽  
Robert H. Hamstra ◽  
Christoph Kündig ◽  
Patrick Camina ◽  
John A. Rogers
Keyword(s):  
Spatial Resolution ◽  
Dynamic Range ◽  
Strong Motion ◽  
The United States ◽  
Companion Paper ◽  
Low Noise ◽  
Practical Reasons ◽  
Wireless Internet ◽  
Urban Centers ◽  
Strong Motion Network

The ability of a strong-motion network to resolve wavefields can be described on three axes: frequency, amplitude, and space. While the need for spatial resolution is apparent, for practical reasons that axis is often neglected. TREMOR is a MEMS-based accelerograph using wireless Internet to minimize lifecycle cost. TREMOR instruments can economically augment traditional ones, residing between them to improve spatial resolution. The TREMOR instrument described here has dynamic range of 96 dB between ±2 g, or 102 dB between ±4 g. It is linear to <1% of full scale (FS), with a response function effectively shaped electronically. We developed an economical, very low noise, accurate (<1%FS) temperature compensation method. Displacement is easily recovered to 10-cm accuracy at full bandwidth, and better with care. We deployed prototype instruments in Oakland, California, beginning in 1998, with 13 now at mean spacing of ∼3 km—one of the most densely instrumented urban centers in the United States. This array is among the quickest in returning (PGA, PGV, Sa) vectors to ShakeMap, ∼75 to 100 s. Some 13 events have been recorded. A ShakeMap and an example of spatial variability are shown. Extensive tests of the prototypes for a commercial instrument are described here and in a companion paper.

scholarly journals Belief Merging Operators as Maximum Likelihood Estimators

2020 ◽  
Author(s):  
Patricia Everaere ◽  
Sebastien Konieczny ◽  
Pierre Marquis
Keyword(s):  
Maximum Likelihood ◽  
Maximum Likelihood Estimators ◽  
Noise Model ◽  
Belief Merging ◽  
The World ◽  
Natural Noise ◽  
True State ◽  
Merging Process ◽  
Rationality Postulates ◽  
Noise Models

We study how belief merging operators can be considered as maximum likelihood estimators, i.e., we assume that there exists a (unknown) true state of the world and that each agent participating in the merging process receives a noisy signal of it, characterized by a noise model. The objective is then to aggregate the agents' belief bases to make the best possible guess about the true state of the world. In this paper, some logical connections between the rationality postulates for belief merging (IC postulates) and simple conditions over the noise model under consideration are exhibited. These results provide a new justification for IC merging postulates. We also provide results for two specific natural noise models: the world swap noise and the atom swap noise, by identifying distance-based merging operators that are maximum likelihood estimators for these two noise models.

Shallow velocity structure and poisson's ratio at the Tarzana, California, strong-motion accelerometer site

1996 ◽  
Vol 86 (6) ◽  
pp. 1704-1713 ◽  
Author(s):  
R. D. Catchings ◽  
W. H. K. Lee
Keyword(s):  
Urban Areas ◽  
Velocity Structure ◽  
Strong Motion ◽  
P Wave ◽  
S Wave ◽  
Near Surface ◽  
Velocity Models ◽  
Wave Velocities ◽  
Poisson's Ratios ◽  
Poisson’S Ratios

Abstract The 17 January 1994, Northridge, California, earthquake produced strong ground shaking at the Cedar Hills Nursery (referred to here as the Tarzana site) within the city of Tarzana, California, approximately 6 km from the epicenter of the mainshock. Although the Tarzana site is on a hill and is a rock site, accelerations of approximately 1.78 g horizontally and 1.2 g vertically at the Tarzana site are among the highest ever instrumentally recorded for an earthquake. To investigate possible site effects at the Tarzana site, we used explosive-source seismic refraction data to determine the shallow (&lt;70 m) P-and S-wave velocity structure. Our seismic velocity models for the Tarzana site indicate that the local velocity structure may have contributed significantly to the observed shaking. P-wave velocities range from 0.9 to 1.65 km/sec, and S-wave velocities range from 0.20 and 0.6 km/sec for the upper 70 m. We also found evidence for a local S-wave low-velocity zone (LVZ) beneath the top of the hill. The LVZ underlies a CDMG strong-motion recording site at depths between 25 and 60 m below ground surface (BGS). Our velocity model is consistent with the near-surface (&lt;30 m) P- and S-wave velocities and Poisson's ratios measured in a nearby (&lt;30 m) borehole. High Poisson's ratios (0.477 to 0.494) and S-wave attenuation within the LVZ suggest that the LVZ may be composed of highly saturated shales of the Modelo Formation. Because the lateral dimensions of the LVZ approximately correspond to the areas of strongest shaking, we suggest that the highly saturated zone may have contributed to localized strong shaking. Rock sites are generally considered to be ideal locations for site response in urban areas; however, localized, highly saturated rock sites may be a hazard in urban areas that requires further investigation.

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