A Seismic Refraction Profile Across the Polar Continental Shelf of the Queen Elizabeth Islands

1971 ◽  
Vol 8 (3) ◽  
pp. 347-360 ◽  
Author(s):  
M. J. Berry ◽  
K. G. Barr
Keyword(s):  
Continental Slope ◽  
Broad Band ◽  
Seismic Refraction ◽  
Low Frequency ◽  
Water Layer ◽  
Noise Levels ◽  
High Background ◽  
Crustal Model ◽  
Seismic Recording ◽  
High Background Noise

During the spring of 1967, a seismic refraction experiment was conducted from the SW tip of Prince Patrick Island in the Queen Elizabeth Islands of Arctic Canada to a point mid-way down the continental slope, some 220 km from the coast.It was found that seismic recording on sea ice was plagued by unusually high background noise levels which could be attributed to low frequency (below 1 Hz) oscillations of the ice pans and to the broad-band noise generated by frequent ice cracking. It was discovered, and is shown theoretically, that seismic wave propagating through a water layer (the ocean) and incident on the ice layer from below provide an exact π/2 phase shift between the horizontal and vertical components of surface motion. This fact can be used to advantage in digital processing.The interpretation shows a crustal model with depths to the M discontinuity of 28 ± 4 km at the coast, thinning to 15 ± 9 km at the end of the profile. The velocity of the mantle is measured as 8.05 ± 0.17 km/s. Mid-way down the continental slope there are 5.0 ± 1.63 km of sediments overlying material with a velocity of 5.36 ± 0.15 km/s. Material of a similar velocity, 5.72 ± 0.18 km/s, lies 2.7 ± 1.9 km beneath the surface material at the coast, where the surface layer has a velocity of 4.76 ± 0.4 km/s. It is concluded that the data support the hypothesis that the Canada Basin has an oceanic rather than a continental crust.

Effects of Classroom Noise on Students and Teachers in Greece

2003 ◽  
Vol 96 (2) ◽  
pp. 539-544 ◽  
Author(s):  
Dimitris Skarlatos ◽  
Manolis Manatakis
Keyword(s):  
High School ◽  
Background Noise ◽  
Reverberation Time ◽  
Noise Levels ◽  
High Background ◽  
High Noise ◽  
Significant Percentage ◽  
Time Period ◽  
High Background Noise

Measurements inside 32 occupied high-school classrooms during the courses showed that the measured long-term equivalent noise levels are high. A significant percentage of students and teachers found these levels unacceptable. The observed noise levels depend on the time period of the course, the age, and the number of the students in each classroom. The large reverberation time and the high background noise are responsible for the measured high noise level.

scholarly journals Decision making in the face of a deadly predator: high-amplitude behavioural thresholds can be adaptive for rainforest crickets under high background noise levels

2020 ◽  
Vol 375 (1802) ◽  
pp. 20190471 ◽  
Author(s):  
Heiner Römer ◽  
Marc Holderied
Keyword(s):  
Background Noise ◽  
Experimental Tests ◽  
High Amplitude ◽  
Decision Criterion ◽  
Target Strength ◽  
False Alarms ◽  
Noise Levels ◽  
High Background ◽  
Ultrasonic Calls ◽  
High Background Noise

Many insect families have evolved ears that are adapted to detect ultrasonic calls of bats. The acoustic sensory cues indicating the presence of a bat are then used to initiate bat avoidance behaviours. Background noise, in particular at ultrasonic frequencies, complicates these decisions, since a response to the background may result in costly false alarms. Here, we quantify bat avoidance responses of small rainforest crickets (Gryllidae, Trigoniinae), which live under conditions of high levels of ultrasonic background noise. Their bat avoidance behaviour exhibits markedly higher thresholds than most other studied eared insects. Their responses do not qualitatively differ at suprathreshold amplitudes up to sound pressure levels of 105 dB. Moreover, they also exhibit evasive responses to single, high-frequency events and do not require the repetitive sequence of ultrasonic calls typical for the search phase of bat echolocation calls. Analysis of bat and katydid sound amplitudes and peak frequencies in the crickets' rainforest habitat revealed that the cricket's behavioural threshold would successfully reject the katydid background noise. Using measurements of the crickets' echo target strength for bat predators, we calculated the detection distances for both predators and prey. Despite their high behavioural threshold, the cricket prey still has a significant detection advantage at frequencies between 20 and 40 kHz. The low-amplitude bat calls they ignore are no predation threat because even much louder calls would be detected before the bat would hear the cricket echo. This leaves ample time for evasive actions. Thus, a simple decision criterion based on a high-amplitude behavioural threshold can be adaptive under the high background noise levels in nocturnal rainforests, in avoiding false alarms and only missing detection for bat calls too far away to pose a risk. This article is part of the theme issue ‘Signal detection theory in recognition systems: from evolving models to experimental tests’.

scholarly journals Caller ID for Risso's and Pacific White-Sided Dolphins

2021 ◽  
Author(s):  
Mahdi Al-Badrawi ◽  
Yue Liang ◽  
Kerri D. Seger ◽  
Christopher M. Foster ◽  
Nicholas J. Kirsch
Keyword(s):  
Ecosystem Dynamics ◽  
The Arctic ◽  
Noise Levels ◽  
Temperate Water ◽  
High Background ◽  
Temporal Properties ◽  
Mode Decomposition ◽  
High Background Noise ◽  
Audio Files ◽  
Water Species

Abstract Climate change affects the distributions of marine mammals1, and some temperate water species are spreading northward into the Arctic Ocean2, 3. Tracking expanding species is crucial to conservation efforts and using automatic detectors and classifiers to track the locations of their vocalizations could help. Risso’s (Gg) and Pacific white-sided (Lo) dolphins were documented spreading poleward2 and make very similar sounds, making it difficult for both human analysts and classification algorithms to tell them apart. Variational Mode Decomposition (VMD) has provided both an easier visualization tool4 for human analysts and offers promising capabilities in separating call types of similar spectral and temporal properties. Here we show a new visualization tool and feature extraction technique using VMD that achieves 81.3% accuracy, even when using audio files with faint signals and high background noise levels and without context clues. Because not all dolphins whistle5–7, being able to distinguish between just their pulsed signals is important for tracking them using as many files as possible from under-sampled areas of the ocean. Automating the VMD method and expanding it to other dolphin species that have very similar pulsive signals will lead to a faster understanding of ecosystem dynamics under a changing climate than can currently be achieved.

scholarly journals Separating overlapping echolocation: An updated method for estimating the number of echolocating animals in high background noise levels

2021 ◽  
Vol 150 (2) ◽  
pp. 709-717
Author(s):  
Rebecca A. Hamilton ◽  
Josefin Starkhammar ◽  
Stefanie K. Gazda ◽  
Richard C. Connor
Keyword(s):  
Background Noise ◽  
Noise Levels ◽  
High Background ◽  
High Background Noise

Integration of Multi-geophysical Approaches to Identify Potential Pathways of Heavy Metals Contamination - A Case Study in Zeida, Morocco

2020 ◽  
Vol 25 (3) ◽  
pp. 415-423
Author(s):  
Ahmed Lachhab ◽  
El Mehdi Benyassine ◽  
Mohamed Rouai ◽  
Abdelilah Dekayir ◽  
Jean C. Parisot ◽  
...  
Keyword(s):  
Heavy Metals ◽  
Seismic Velocity ◽  
Seismic Refraction ◽  
Geophysical Methods ◽  
Low Frequency ◽  
Electrical Current ◽  
P Wave ◽  
Low Resistivity ◽  
Refraction Tomography ◽  
Geophysical Surveys

The tailings of Zeida's abandoned mine are found near the city of Midelt, in the middle of the high Moulouya watershed between the Middle and the High Atlas of Morocco. The tailings occupy an area of about 100 ha and are stored either in large mining pit lakes with clay-marl substratum or directly on a heavily fractured granite bedrock. The high contents of lead and arsenic in these tailings have transformed them into sources of pollution that disperse by wind, runoff, and seepage to the aquifer through faults and fractures. In this work, the main goal is to identify the pathways of contaminated water with heavy metals and arsenic to the local aquifers, water ponds, and Moulouya River. For this reason, geophysical surveys including electrical resistivity tomography (ERT), seismic refraction tomography (SRT) and very low-frequency electromagnetic (VLF-EM) methods were carried out over the tailings, and directly on the substratum outside the tailings. The result obtained from combining these methods has shown that pollutants were funneled through fractures, faults, and subsurface paleochannels and contaminated the hydrological system connecting groundwater, ponds, and the river. The ERT profiles have successfully shown the location of fractures, some of which extend throughout the upper formation to depths reaching the granite. The ERT was not successful in identifying fractures directly beneath the tailings due to their low resistivity which inhibits electrical current from propagating deeper. The seismic refraction surveys have provided valuable details on the local geology, and clearly identified the thickness of the tailings and explicitly marked the boundary between the Triassic formation and the granite. It also aided in the identification of paleochannels. The tailings materials were easily identified by both their low resistivity and low P-wave velocity values. Also, both resistivity and seismic velocity values rapidly increased beneath the tailings due to the compaction of the material and lack of moisture and have proven to be effective in identifying the upper limit of the granite. Faults were found to lie along the bottom of paleochannels, which suggest that the locations of these channels were caused by these same faults. The VLF-EM surveys have shown tilt angle anomalies over fractured areas which were also evinced by low resistivity area in ERT profiles. Finally, this study showed that the three geophysical methods were complementary and in good agreement in revealing the pathways of contamination from the tailings to the local aquifer, nearby ponds and Moulouya River.

scholarly journals The Low-Frequency Array (LOFAR): Opening a New Window on the Universe

2002 ◽  
Vol 199 ◽  
pp. 474-483
Author(s):  
Namir E. Kassim ◽  
T. Joseph W. Lazio ◽  
William C. Erickson ◽  
Patrick C. Crane ◽  
R. A. Perley ◽  
...  
Keyword(s):  
Angular Resolution ◽  
Broad Band ◽  
Low Frequency ◽  
Electromagnetic Spectrum ◽  
Interferometric Imaging ◽  
Very Large Array ◽  
Long Wavelength ◽  
Calibration Techniques ◽  
Long Baselines ◽  
The Universe

Decametric wavelength imaging has been largely neglected in the quest for higher angular resolution because ionospheric structure limited interferometric imaging to short (< 5 km) baselines. The long wavelength (LW, 2—20 m or 15—150 MHz) portion of the electromagnetic spectrum thus remains poorly explored. The NRL-NRAO 74 MHz Very Large Array has demonstrated that self-calibration techniques can remove ionospheric distortions over arbitrarily long baselines. This has inspired the Low Frequency Array (LOFAR)—-a fully electronic, broad-band (15—150 MHz)antenna array which will provide an improvement of 2—3 orders of magnitude in resolution and sensitivity over the state of the art.

scholarly journals The challenging SED of AP Librae

2011 ◽  
Vol 7 (S284) ◽  
pp. 411-413 ◽  
Author(s):  
David Sanchez ◽  
Berrie Giebels ◽  
Pascal Fortin ◽  
Keyword(s):  
Spectral Energy Distribution ◽  
Broad Band ◽  
Low Frequency ◽  
Theoretical Models ◽  
Intermediate Frequency ◽  
High Energy ◽  
Spectral Energy ◽  
Broad Band Emission ◽  
Band Emission ◽  
Bl Lac

AbstractMatching the broad-band emission of active galaxies with the predictions of theoretical models can be used to derive constraints on the properties of the emitting region and to probe the physical processes involved. AP Librae is the third low frequency peaked BL Lac (LBL) detected at very high energy (VHE, E>100GeV) by an Atmospheric Cherenkov Telescope; most VHE BL Lacs (34 out of 39) belong to the high-frequency and intermediate-frequency BL Lac classes (HBL and IBL). LBL objects tend to have a higher luminosity with lower peak frequencies than HBLs or IBLs. The characterization of their time-averaged spectral energy distribution is challenging for emission models such as synchrotron self-Compton (SSC) models.

Incubator Noise

PEDIATRICS ◽  
1975 ◽  
Vol 56 (4) ◽  
pp. 617-617
Author(s):  
Gōsta Blennow ◽  
Nils W. Svenningsen ◽  
Bengt Almquist
Keyword(s):  
Low Frequency ◽  
Sound Level ◽  
Noise Levels ◽  
Frequency Sound ◽  
Mechanical Noise ◽  
Sound Levels ◽  
Infant Incubator ◽  
Improved Model ◽  
Model C

Recently we reported results from studies of incubator noise levels.1 It was found that in certain types of incubators the noise was considerable, and attention was called to the sound level in the construction of new incubators. Recently we had the opportunity to study an improved model of Isolette Infant Incubator Model C-86 where the mechanical noise from the electrically powered motor has been partially eliminated. With this modification it has been possible to lower the low-frequency sound levels to a certain degree in comparison to the levels registered in our study.

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