The effect of surface noise in low‐frequency passive detection in coastal waters

1997 ◽  
Vol 101 (5) ◽  
pp. 3197-3197
Author(s):  
William M. Sanders ◽  
Frederick D. Tappert
Keyword(s):  
Coastal Waters ◽  
Low Frequency ◽  
Passive Detection ◽  
Surface Noise ◽  
Effect Of Surface

scholarly journals Eddy-Induced Growth Rate of Low-Frequency Variability and Its Mid- to Late Winter Suppression in the Northern Hemisphere

2014 ◽  
Vol 71 (7) ◽  
pp. 2281-2298 ◽  
Author(s):  
Hong-Li Ren ◽  
Fei-Fei Jin ◽  
Jong-Seong Kug
Keyword(s):  
Northern Hemisphere ◽  
Storm Track ◽  
Low Frequency ◽  
Lower Troposphere ◽  
Surface Friction ◽  
Late Winter ◽  
Wind Maximum ◽  
Low Frequency Variability ◽  
Storm Track Activity ◽  
Effect Of Surface

Abstract Synoptic eddy and low-frequency flow (SELF) feedback plays an important role in reinforcing low-frequency variability (LFV). Recent studies showed that an eddy-induced growth (EIG) or instability makes a fundamental contribution to the maintenance of LFV. To quantify the efficiency of the SELF feedback, this study examines the spatiotemporal features of the empirical diagnostics of EIG and its associations with LFV. The results show that, in terms of eddy vorticity forcing, the EIG rate of LFV is generally larger (smaller) in the upper (lower) troposphere, whereas, in terms of eddy potential vorticity forcing, it is larger in the lower troposphere to partly balance the damping effect of surface friction. The local EIG rate shows a horizontal spatial distribution that corresponds to storm-track activity, which tends to be responsible for maintaining LFV amplitudes and patterns as well as sustaining eddy-driven jets. In fact, the EIG rate has a well-defined seasonality, being generally larger in cold seasons and smaller in the warmest season, and this seasonality is stronger in the Northern Hemisphere than in the Southern Hemisphere. This study also reveals a mid- to late winter (January–March) suppression of the EIG rate in the Northern Hemisphere, which indicates a reduced eddy feedback efficiency and may be largely attributed to the eddy kinetic energy suppression and the midlatitude zonal wind maximum in the midwinter of the Northern Hemisphere.

scholarly journals Monitoring the circulation of coastal waters off the Southern coast of Crimea

2019 ◽  
Vol 485 (4) ◽  
pp. 507-510
Author(s):  
V. A. Ivanov ◽  
A. S. Kuznetsov ◽  
A. N. Morozov
Keyword(s):  
Spectral Analysis ◽  
Coastal Zone ◽  
Coastal Waters ◽  
Low Frequency ◽  
Water Dynamics ◽  
Southern Coast ◽  
Jet Streams ◽  
Integrated Monitoring ◽  
Low Frequency Oscillations ◽  
The Crimea

The paper presents the results of integrated monitoring of water dynamics in the coastal zone off the Southern coast of the Crimea for 2008-2016. The regime and features of circulation of coastal waters were determined. An intensive contribution of low-frequency oscillations of coastal currents at the seasonal and synoptic scales was identified based on the results of spectral analysis of a nine-year set of vector dynamics series. For water fluctuations in the coastal zone, the alongshore structure of reciprocating jet streams caused by water dynamics at the shelf and continental slope dominates.

Low‐frequency ocean surface noise sources

1985 ◽  
Vol 78 (S1) ◽  
pp. S1-S2 ◽  
Author(s):  
W. M. Carey ◽  
M. P. Bradley
Keyword(s):  
Low Frequency ◽  
Ocean Surface ◽  
Noise Sources ◽  
Surface Noise

The Effect of Surface Orientation on the Perception of Stereoscopic Corrugations

Perception ◽  
1996 ◽  
Vol 25 (1_suppl) ◽  
pp. 117-117 ◽  
Author(s):  
A D Parton ◽  
M F Bradshaw ◽  
B J Rogers ◽  
I R L Davies
Keyword(s):  
Three Dimensional ◽  
Low Frequency ◽  
Surface Orientation ◽  
Detection Task ◽  
Matching Task ◽  
Threshold Detection ◽  
Corrugated Surfaces ◽  
Rate Of Increase ◽  
Effect Of Surface

For most observers there is a pronounced orientational anisotropy in the perception of three-dimensional corrugated surfaces (Rogers and Graham, 1983 Science221 1409 – 1411; Bradshaw and Rogers, 1993 Perception22 Supplement, 117). Low-frequency corrugations which are oriented vertically have been found to have higher disparity modulation thresholds, the amount of perceived depth at suprathreshold levels is smaller, and typically they take longer to see than horizontally oriented corrugations. In the present experiments, the orientation of the corrugations was manipulated (from horizontal to vertical in 22.5 deg increments) to investigate the effect of surface orientation on both (i) a threshold detection task and (ii) a suprathreshold depth-matching task. The stimuli were 10 deg in diameter and were presented on two 12 inch monochrome monitors arranged to form a Wheatstone stereoscope. The surfaces were modulated in depth at four different corrugation frequencies (from 0.1 to 0.8 cycle deg−1 in octave steps). Thresholds were found to increase monotonically with increasing surface orientation from the horizontal: ∼2.5 arc s for horizontal corrugations to ∼10 arc s for vertical corrugations. The increase in thresholds was less marked for surfaces with higher corrugation frequencies. The rate of increase of threshold was greatest for surface orientations beyond 45°. A different pattern of results was found in the suprathreshold depth-matching task. Although the perceived depth in vertically oriented corrugations was significantly smaller (>50%) than for horizontally oriented corrugations, the largest amount of perceived depth was found for corrugated surfaces oriented at 45°. These results suggest that the disparity information used to process stereoscopic corrugations at threshold may be different from that used to process suprathreshold surfaces.

Rectangular wave eddy current testing using for imaging of backside defects of steel plates

2020 ◽  
Vol 64 (1-4) ◽  
pp. 255-262
Author(s):  
Teruyoshi Sasayama ◽  
Wataru Yoshimura ◽  
Keiji Enpuku
Keyword(s):  
Eddy Current ◽  
Low Frequency ◽  
Harmonic Signal ◽  
Eddy Current Testing ◽  
Steel Plates ◽  
Magnetic Noise ◽  
Rectangular Wave ◽  
Current Testing ◽  
Thick Steel ◽  
Surface Noise

Accurate, easy, and fast inspection of defects on the backside of thick steel plates is essential for the maintenance of infrastructures. Low frequency eddy current testing (LF-ECT) is a promising method to detect defects of the backside of steel plates, with a thickness of approximately 10 mm. However, it is possible that the signal from the backside defect is smaller than that from the surface magnetic noise, causing difficulty identifying the backside defect. In this study, we propose a method to reduce the surface noise by employing a square wave inverter to generate a harmonic signal (rectangular wave ECT, or RECT), and the result demonstrates that the surface noise is successfully reduced using the harmonic signal.

Distribution, abundance, population structure and activity of Halobatrachus didactylus in the Tagus estuary (Portugal) and adjacent coastal waters

2011 ◽  
Vol 93 (2) ◽  
pp. 405-412 ◽  
Author(s):  
João Carlos Cotter ◽  
Tadeu José Pereira ◽  
Maria José Costa ◽  
José Lino Costa
Keyword(s):  
Population Structure ◽  
Coastal Waters ◽  
Low Frequency ◽  
Late Summer ◽  
Tagus Estuary ◽  
Water Current ◽  
Western Coast ◽  
Distinct Features ◽  
Discrete Populations ◽  
Structure And Activity

The Lusitanian toadfish Halobatrachus didactylus is a demersal teleost and the only species of the family Batrachoididae that occurs along the continental Portuguese coast. It is a subtropical species that is more abundant in the south of Portugal, whereas along the western coast it is concentrated in discrete populations, located in estuaries and coastal recesses. The distinct features of these estuaries have revealed important changes in the respective Lusitanian toadfish populations, namely particularities in their distribution and population structure, and also in the morphology and breeding behaviour of the specimens. A survey covering 31 stations in the Tagus estuary, Portugal, and adjacent coastal waters sampled these stations over an 18 month period. This study characterized the distribution, abundance, population structure and activity of H. didactylus in this coastal zone. Toadfish showed a preferential distribution in the intermediate and lower estuarine stretches, and was more abundant in the Montijo Bay, a small bay within the Tagus estuary. Three length-groups were identified, with larger specimens more abundant in deeper areas. The specimens also revealed a preference for areas of higher water temperature, low water current and muddy substrates. Female specimens were slightly more abundant than males and type II males had a very low frequency of occurrence (3.2%). Captures of toadfish were high in spring and late summer and very low in winter.

Seismic sensing of extremely-low-frequency sounds in coastal waters

2005 ◽  
Author(s):  
A. Barbagelata ◽  
E. Michelozzi ◽  
D. Rauch ◽  
B. Schmalfeldt
Keyword(s):  
Coastal Waters ◽  
Low Frequency ◽  
Extremely Low Frequency

scholarly journals A 2-decade (1988–2009) record of diatom fluxes in the Mauritanian coastal upwelling: impact of low-frequency forcing and a two-step shift in the species composition

2021 ◽  
Vol 18 (5) ◽  
pp. 1873-1891
Author(s):  
Oscar E. Romero ◽  
Simon Ramondenc ◽  
Gerhard Fischer
Keyword(s):  
Coastal Waters ◽  
Temporal Dynamics ◽  
Southern Oscillation ◽  
Low Frequency ◽  
Meridional Overturning Circulation ◽  
Benthic Diatoms ◽  
Time Interval ◽  
Data Set ◽  
The Impact

Abstract. Eastern boundary upwelling ecosystems (EBUEs) are among the most productive marine regions in the world's oceans. Understanding the degree of interannual to decadal variability in the Mauritania upwelling system is crucial for the prediction of future changes of primary productivity and carbon sequestration in the Canary Current EBUE as well as in similar environments. A multiyear sediment trap experiment was conducted at the mooring site CBmeso (“Cape Blanc mesotrophic”, ca. 20∘ N, ca. 20∘40′ W) in the highly productive coastal waters off Mauritania. Here, we present results on fluxes of diatoms and the species-specific composition of the assemblage for the time interval between March 1988 and June 2009. The temporal dynamics of diatom populations allows the proposal of three main intervals: (i) early 1988–late 1996, (ii) 1997–1999, and (iii) early 2002–mid 2009. The Atlantic Multidecadal Oscillation (AMO) appears to be an important driver of the long-term dynamics of diatom population. The long-term AMO-driven trend is interrupted by the occurrence of the strong 1997 El Niño–Southern Oscillation (ENSO). The extraordinary shift in the relative abundance of benthic diatoms in May 2002 suggests the strengthening of offshore advective transport within the uppermost layer of filament waters and in the subsurface and in deeper and bottom-near layers. It is hypothesized that the dominance of benthic diatoms was the response of the diatom community to the intensification of the slope and shelf poleward undercurrents. This dominance followed the intensification of the warm phase of AMO and the associated changes of the Atlantic Meridional Overturning Circulation. Transported valves (siliceous remains) from shallow Mauritanian coastal waters into the bathypelagic should be considered for the calculation and model experiments of bathy- and pelagic nutrients budgets (especially Si), the burial of diatoms, and the paleoenvironmental signal preserved in downcore sediments. Additionally, our 1988–2009 data set contributes to the characterization of the impact of low-frequency climate forcings in the northeastern Atlantic and will be especially helpful for establishing the scientific basis for forecasting and modeling future states of the Canary Current EBUE and its decadal changes.

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