scholarly journals Urban Running Activity Detected Using a Seismic Sensor during COVID-19 Pandemic

2021 ◽  
Author(s):  
Yumin Zhao ◽  
Yunyue Elita Li ◽  
Enhedelihai Nilot ◽  
Gang Fang
Keyword(s):  
Seismic Data ◽  
Urban Environments ◽  
Outdoor Environment ◽  
Multiple Sources ◽  
Screening Criteria ◽  
Essential Information ◽  
Human Foot ◽  
Running Activity ◽  
Seismic Sensors ◽  
Primary Frequency

Abstract Human foot traffic in urban environments provides essential information for city planners to manage the urban resources and urban residents to plan their activities. Compared to camera or mobile-based solutions, seismic sensors detect human footstep signals with fewer privacy concerns. However, seismic sensors often record signals generated from multiple sources, particularly in an urban outdoor environment. In this article, we monitor people’s running activities during COVID-19 pandemic with a seismic sensor in a park in Singapore. We compare the spectra of natural and urban events in the recorded seismic data. For each 3 s seismic data, we define hierarchical screening criteria to identify footsteps based on the spectrum of the signal and its envelope. We derive the cadence of each runner by detecting the primary frequency of the footstep signals. The resulting algorithm achieves higher accuracy and higher temporal resolution for weak and overlapping signals compared to existing methods. Runner statistics based on four-month long seismic data show that urban running activities have clear daily and weekly cycles. Lockdown measures to mitigate COVID-19 pandemic promoted running activities, particularly over the weekends. Cadence statistics show that morning runners have higher cadence on average.

scholarly journals Passive seismic event estimation using multiscattering waveform inversion

Geophysics ◽  
2019 ◽  
Vol 84 (3) ◽  
pp. KS59-KS69 ◽  
Author(s):  
Chao Song ◽  
Zedong Wu ◽  
Tariq Alkhalifah
Keyword(s):  
Seismic Data ◽  
Waveform Inversion ◽  
Velocity Model ◽  
Source Image ◽  
Time Inversion ◽  
Multiple Sources ◽  
Origin Time ◽  
Secondary Sources ◽  
Velocity Models ◽  
Passive Seismic

Passive seismic monitoring has become an effective method to understand underground processes. Time-reversal-based methods are often used to locate passive seismic events directly. However, these kinds of methods are strongly dependent on the accuracy of the velocity model. Full-waveform inversion (FWI) has been used on passive seismic data to invert the velocity model and source image, simultaneously. However, waveform inversion of passive seismic data uses mainly the transmission energy, which results in poor illumination and low resolution. We developed a waveform inversion using multiscattered energy for passive seismic to extract more information from the data than conventional FWI. Using transmission wavepath information from single- and double-scattering, computed from a predicted scatterer field acting as secondary sources, our method provides better illumination of the velocity model than conventional FWI. Using a new objective function, we optimized the source image and velocity model, including multiscattered energy, simultaneously. Because we conducted our method in the frequency domain with a complex source function including spatial and wavelet information, we mitigate the uncertainties of the source wavelet and source origin time. Inversion results from the Marmousi model indicate that by taking advantage of multiscattered energy and starting from a reasonably acceptable frequency (a single source at 3 Hz and multiple sources at 5 Hz), our method yields better inverted velocity models and source images compared with conventional FWI.

Recording the Aurora at Seismometers across Alaska

2020 ◽  
Vol 91 (6) ◽  
pp. 3039-3053 ◽  
Author(s):  
Carl Tape ◽  
Adam T. Ringler ◽  
Don L. Hampton
Keyword(s):  
Magnetic Field ◽  
Seismic Data ◽  
Vertical Component ◽  
Seismic Array ◽  
Magnetic Shielding ◽  
Data Sets ◽  
S Waves ◽  
Auroral Activity ◽  
Seismic Sensors ◽  
Magnetometer Data

Abstract We examine three continuously recording data sets related to the aurora: all-sky camera images, three-component magnetometer data, and vertical-component, broadband seismic data as part of the EarthScope project (2014 to present). Across Alaska there are six all-sky cameras, 13 magnetometers, and >200 seismometers. The all-sky images and magnetometers have the same objective, which is to monitor space weather and improve our understanding of auroral activity, including the influence on magnetic fields in the ground. These variations in the magnetic field are also visible on seismometers, to the extent that during an auroral event, the long-period (40–800 s) waves recorded by a seismometer are magnetic field variations, not true ground motion. Although this is a problem—one that can be rectified with magnetic shielding at each seismometer site—it is also an opportunity because the present seismic array in Alaska is much broader than the coverage by magnetometers and all-sky cameras. Here we focus on three aurora events and document a direct link between aurora images in the night sky and seismometer recordings on ground. Simultaneous recordings by magnetometers provide a critical link between the sky images and the seismometer recordings. We document qualitative correlations among sky, magnetic, and seismic data. The findings suggest that the signature of auroral activity is widespread across seismometers in Alaska, implying that the seismic array could be used to enhance the spatial resolution of the existing network of all-sky cameras and magnetometers. Future efforts to improve the multisensor seismic stations in Alaska, for the purpose of monitoring seismic and auroral activity, should consider installation of all-sky cameras, installation of magnetometers, and magnetic shielding of seismic sensors.

scholarly journals A Study of Visual Descriptors for Outdoor Navigation Using Google Street View Images

2016 ◽  
Vol 2016 ◽  
pp. 1-12 ◽  
Author(s):  
L. Fernández ◽  
L. Payá ◽  
O. Reinoso ◽  
L. M. Jiménez ◽  
M. Ballesta
Keyword(s):  
Visual Information ◽  
Visual Navigation ◽  
Urban Environments ◽  
Outdoor Environment ◽  
Localization Algorithm ◽  
Google Street View ◽  
Street View ◽  
Visual Descriptors ◽  
Outdoor Environments ◽  
Panoramic Images

A comparative analysis between several methods to describe outdoor panoramic images is presented. The main objective consists in studying the performance of these methods in the localization process of a mobile robot (vehicle) in an outdoor environment, when a visual map that contains images acquired from different positions of the environment is available. With this aim, we make use of the database provided by Google Street View, which contains spherical panoramic images captured in urban environments and their GPS position. The main benefit of using these images resides in the fact that it permits testing any novel localization algorithm in countless outdoor environments anywhere in the world and under realistic capture conditions. The main contribution of this work consists in performing a comparative evaluation of different methods to describe images to solve the localization problem in an outdoor dense map using only visual information. We have tested our algorithms using several sets of panoramic images captured in different outdoor environments. The results obtained in the work can be useful to select an appropriate description method for visual navigation tasks in outdoor environments using the Google Street View database and taking into consideration both the accuracy in localization and the computational efficiency of the algorithm.

Imaging passive seismic data

Geophysics ◽  
2006 ◽  
Vol 71 (4) ◽  
pp. SI177-SI187 ◽  
Author(s):  
Brad Artman
Keyword(s):  
Water Table ◽  
Seismic Data ◽  
Survey Design ◽  
Signal To Noise Ratio ◽  
Multiple Sources ◽  
Depth Migration ◽  
Reflection Seismic ◽  
Ambient Sound ◽  
Passive Seismic ◽  
Passive Data

Imaging passive seismic data is the process of synthesizing the wealth of subsurface information available from reflection seismic experiments by recording ambient sound using an array of geophones distributed at the surface. Crosscorrelating the traces of such a passive experiment can synthesize data that are identical to actively collected reflection seismic data. With a correlation-based imaging condition, wave-equation shot-profile depth migration can use raw transmission wavefields as input for producing a subsurface image. Migration is even more important for passively acquired data than for active data because with passive data, the source wavefields are likely to be weak compared with background and instrument noise — a condition that leads to a low signal-to-noise ratio. Fourier analysis of correlating long field records shows that aliasing of the wavefields from distinct shots is unavoidable. Although this reduces the order of computations for correlation by the length of the original trace, the aliasing produces an output volume that may not be substantially more useful than the raw data because of the introduction of crosstalk between multiple sources. Direct migration of raw field data still can produce an accurate image, even when the transmission wavefields from individual sources are not separated. To illustrate direct migration, I use images from a shallow passive seismic investigation targeting a buried hollow pipe and the water-table reflection. These images show a strong anomaly at the 1-m depth of the pipe and faint events that could be the water table at a depth of around [Formula: see text]. The images are not clear enough to be irrefutable. I identify deficiencies in survey design and execution to aid future efforts.

scholarly journals Seismic monitoring of urban activity in Barcelona during COVID-19 lockdown

2020 ◽  
Author(s):  
Jordi Diaz ◽  
Mario Ruiz ◽  
José-Antonio Jara
Keyword(s):  
Human Activity ◽  
Seismic Noise ◽  
Urban Environments ◽  
Residential Areas ◽  
Construction Sites ◽  
Seismic Amplitude ◽  
Seismic Sensors ◽  
Level Of Activity ◽  
Seismic Vibrations ◽  
The City

Abstract. The city of Barcelona has been covered during the COVID-19 pandemic lockdown by a dense seismic network consisting of up to 19 seismic sensors. This network has provided an excellent tool to investigate in detail the background seismic noise variations associated to the lockdown measures. Permanent stations facilitate to compare the seismic noise recorded during the lockdown quieting with long-term variations due to holiday periods. On the other hand, the data acquired by the dense network show the differences between sites located near industrial areas, transportation hubs or residential areas. The results confirm that the quieting of human activity during lockdown has resulted in a reduction of seismic vibrations in the 2–20 Hz band clearly higher than during holiday seasons. This effect is observed throughout the city, but only those stations not affected by very proximal sources of vibration (construction sites, industries) are clearly correlated with the level of activity denoted by other indicators. Our contribution demonstrates that seismic amplitude variations can be used as a proxy for human activity in urban environments, providing details similar to those offered by other mobility indicators.

The Autotrix: Design and Implementation of an Autonomous Urban Driving System

2011 ◽  
Vol 403-408 ◽  
pp. 3884-3891
Author(s):  
Animesh Garg ◽  
Anju Toor ◽  
Sahil Thakkar ◽  
Shiwangi Goel ◽  
Sachin Maheshwari ◽  
...  
Keyword(s):  
Real Time ◽  
Obstacle Avoidance ◽  
Situational Awareness ◽  
Continuous Mapping ◽  
Digital Camera ◽  
Autonomous Driving ◽  
Urban Environments ◽  
Multiple Sources ◽  
Time Data ◽  
Autonomous Guided Vehicle

The Autotrix is an interactive, intelligent, Autonomous Guided Vehicle (AGV) designed to serve in urban environments. Autonomous ground vehicle navigation requires the integration of many technologies such as path planning, odometry, control, obstacle avoidance and situational awareness. The objective of this project is for this prototype to navigate autonomously in an urban environment and reach its destination while detecting and avoiding obstacles on the path .This will be achieved by extracting information from multiple sources of real-time data including digital camera, GPS &ultra sonic sensors, collecting data from this extracted information, processing this data and send controlling instructions to our platform (Autotrix). The significance of this work is in presenting the methods needed for real time navigation; GPS based continuous mapping and obstacle avoidance for intelligent autonomous driving systems.

scholarly journals Seismic monitoring of urban activity in Barcelona during the COVID-19 lockdown

Solid Earth ◽  
2021 ◽  
Vol 12 (3) ◽  
pp. 725-739
Author(s):  
Jordi Diaz ◽  
Mario Ruiz ◽  
José-Antonio Jara
Keyword(s):  
Human Activity ◽  
Seismic Noise ◽  
Urban Environments ◽  
Residential Areas ◽  
Construction Sites ◽  
Seismic Amplitude ◽  
Seismic Sensors ◽  
Level Of Activity ◽  
Seismic Vibrations ◽  
The City

Abstract. During the COVID-19 pandemic lockdown, the city of Barcelona was covered by a dense seismic network consisting of up to 19 seismic sensors. This network has provided an excellent tool to investigate in detail the background seismic-noise variations associated with the lockdown measures. Permanent stations facilitate comparing the seismic noise recorded during the lockdown quieting with long-term variations due to holiday periods. On the other hand, the data acquired by the dense network show the differences between sites located near industrial areas, transportation hubs or residential areas. The results confirm that the quieting of human activity during lockdown has resulted in a reduction in seismic vibrations in the 2–20 Hz band that is clearly higher than during holiday seasons. This effect is observed throughout the city, but only those stations not affected by very proximal sources of vibration (construction sites, industries) are clearly correlated with the level of activity denoted by other indicators. Our contribution demonstrates that seismic amplitude variations can be used as a proxy for human activity in urban environments, providing details similar to those offered by other mobility indicators.

scholarly journals On the complementariness of infrasound and seismic sensors for monitoring snow avalanches

2011 ◽  
Vol 11 (8) ◽  
pp. 2355-2370 ◽  
Author(s):  
A. Kogelnig ◽  
E. Suriñach ◽  
I. Vilajosana ◽  
J. Hübl ◽  
B. Sovilla ◽  
...  
Keyword(s):  
Sound Source ◽  
Seismic Data ◽  
Flow Regimes ◽  
Test Site ◽  
Snow Avalanches ◽  
Avalanche Size ◽  
Average Speed ◽  
Seismic Sensors ◽  
Suspension Layer ◽  
Infrasound Signal

Abstract. The paper analyses and compares infrasonic and seismic data from snow avalanches monitored at the Vallée de la Sionne test site in Switzerland from 2009 to 2010. Using a combination of seismic and infrasound sensors, it is possible not only to detect a snow avalanche but also to distinguish between the different flow regimes and to analyse duration, average speed (for sections of the avalanche path) and avalanche size. Different sensitiveness of the seismic and infrasound sensors to the avalanche regimes is shown. Furthermore, the high amplitudes observed in the infrasound signal for one avalanche were modelled assuming that the suspension layer of the avalanche acts as a moving turbulent sound source. Our results show reproducibility for similar avalanches on the same avalanche path.

scholarly journals Experimental Gait Analysis to Study Stress Distribution of the Human Foot

2017 ◽  
Vol 2017 ◽  
pp. 1-13 ◽  
Author(s):  
Vidya K. Nandikolla ◽  
Robin Bochen ◽  
Steven Meza ◽  
Allan Garcia
Keyword(s):  
Gait Analysis ◽  
Measurement System ◽  
Healthy Subjects ◽  
Force Measurement ◽  
Metatarsophalangeal Joint ◽  
The Body ◽  
Heel Strike ◽  
Human Foot ◽  
Running Activity ◽  
Pressure Peak

Researchers and clinicians are increasingly using plantar pressure and force measurement system to evaluate foot functions. This research evaluates the quality and reliability of a Tekscan HR mat to study the plantar pressures and forces acting during walking, running, jumping, and standing of healthy subjects. The following regions of the foot were investigated: heel, mid foot, metatarsophalangeal joint, hallux, and the toes. The arches of both feet of the three healthy subjects in the gait analysis were presented which addresses the balancing issues of the body during locomotion. The results indicated that the peaks at the big toe (79.4 ± 8.5 N/cm2, p = 0.0001) were the maximum compared to forefoot (40.3 ± 3.3 N/cm2, p = 0.001), to midfoot (7.5 ± 1.3 N/cm2, p = 0.001), and to heel (27.8 ± 3.9 N/cm2, p = 0.0002) for jump activity. The running activity demonstrated similar results as jump where the maximum peak pressures were absorbed at the big toe region. The heel region during running (86.3 ± 12.6 N/cm2, p = 0.001) showed three times the pressure peak compared to the jump land (27.8 ± 3.9 N/cm2, p = 0.0002) activity. The measurement system proved to be highly capable of detecting heel strike and toe-off moments.

Interface prediction ahead of the excavation front by the tunnel-seismic-while-drilling (TSWD) method

Geophysics ◽  
2007 ◽  
Vol 72 (4) ◽  
pp. G39-G44 ◽  
Author(s):  
Lorenzo Petronio ◽  
Flavio Poletto ◽  
Andrea Schleifer
Keyword(s):  
Seismic Data ◽  
Reference Signal ◽  
Tunnel Boring Machine ◽  
S Wave ◽  
Tunnel Boring ◽  
Vertical Seismic Profiling ◽  
Mechanical Excavation ◽  
Seismic Sensors ◽  
Interface Prediction ◽  
Interval Velocities

Predicting geologic interfaces ahead of a tunnel front is of major importance when boring tunnels. Unexpected variations in ground properties can cause problems for tunnel-boring advance and risk for human safety. The tunnel-seismic-while-drilling (TSWD) method utilizes noise produced during mechanical excavation to obtain interpretable seismic data. This passive method uses accelerometers mounted on the advancing tunnel-boring machine (reference signals) together with seismic sensors located along and outside the tunnel. Data recorded by fixed sensors are crosscorrelated with the reference signal and sorted by offset. Similar to reverse vertical seismic profiling, crosscorrelated TSWD data are processed to extract the reflected wavefield. During mechanical excavation of a [Formula: see text] tunnel through upper Triassic dolomite, a survey was performed to predict geologic interfaces. Faults intersecting the tunnel were observed on seismic TSWD data and later were confirmed by geostructural inspection. P- and S-wave interval velocities obtained by TSWD data along the bored tunnel were used to compute dynamic rock moduli to support tunnel completion.

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