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(a) Acoustic propagation from two sources and two receivers forming parallel paths and (b) sample amplitude time series showing a time delay between scintillation events.
Source publication
A self-contained acoustical scintillation instrument is described that has been used to measure flow and turbulence characteristics in two diverse oceanographic settings. This instrument is a battery-operated and internally logging acoustic propagation system that is ideally suited to monitor long-term flow and small- scale effective refractive ind...
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... its simplest configuration (Fig. 1a), two sources transmit an acoustic pulse and are received at two re- ceivers. Both transducers are perpendicular to the ...
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... the current speed. The mean travel time difference shown in Fig. 9, however, is approximately 0 ms, which implies that the transmitter and receiver ar- rays are, on average, parallel, giving the mean flow that is resolved along the transducer array direction, which is assumed to be predominantly along channel. The flow result is shown Fig. 10, together with available along-channel current meter measurements (resolved along 30°T) at a depth of 64 m for comparison. After 1.5 days the meter failed because of clogging of the rotor and vane. Over the 5.5-day measurement period much variability exists in the flow. In fact, the acoustic measurement sensitivity can be improved by ...
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... because of clogging of the rotor and vane. Over the 5.5-day measurement period much variability exists in the flow. In fact, the acoustic measurement sensitivity can be improved by averaging over 5 min. The log-amplitude variance that is shown is within the weak scattering regime ( 2 0.25). The measurement of C 2 n eff from (8) is also shown in Fig. 10. Independent measurements of the finescale tempera- ture/salinity structure were not obtained during this ex- perimental program, but previous measurements in this area (Di Iorio and Yüce 1999), however, showed that turbulent velocity dominated the acoustic scattering be- cause the refractive index variations from the tempera- ...
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... increased separation of the isohalines (and isotherms) at the interfacial zone, however, remained above 60 m and is highly dependent on what happens upstream within the Bosporus Strait. Figure 11 shows a profile of the temperature and salin- ity together with an expanded view of the data sur- rounding the depth of the transmitter (T) and receiver (R), including the sound speed with no pressure effects. ...
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... measurements of in Fig. 10 range from 4 10 6 to 1 10 4 W kg 1 . Assuming that the measure- ments are made in a constant stress layer, the bottom FIG. 11. Temperature/salinity profile taken at the south mooring location, together with an expanded scale of the Mediterranean water surrounding the transmitter (T) and receiver (R) depths. The sound speed is also ...
Citations
... An abundance of reports on the scintillation method to monitor horizontal and vertical flow is available in the acoustic and oceanographic literature [37][38][39]49,50 . The scintillation method in its simplest configuration consists of two transmitters emitting acoustic pulses in succession at a fast repetition rate. ...
... The ASFM, deployed in GC600, has been used in a variety of other deep-sea environments to monitor Mediterranean flow into the Black Sea and hydrothermal plume dynamics 38,49,50 . As depicted in Fig. 1c, using moorings carefully positioned 96.3 m apart, the transmitter and receiver arrays were deployed such that the acoustic propagation paths intersect the bubble stream at ~ 20 mab. ...
Natural hydrocarbon seeps are ubiquitous along continental margins. Despite their significance, we lack a basic understanding of the long-term temporal variability of seep dynamics, including bubble size, rise velocity, composition, and upwelling and entrainment processes. The shortcoming makes it difficult to constrain the global estimates of oil and gas entering the marine environment. Here we report on a multi-method approach based on optical, acoustic, satellite remote sensing, and simulations, to connect the characteristics of a hydrocarbon seep in the Gulf of Mexico to its footprint on the sea surface. Using an in-situ camera, bubble dynamics at the source were measured every 6 h over 153 days and the integrated total hydrocarbon release volume was estimated as 53 m³. The vertical velocity was acoustically measured at 20 m above bed (mab) and found to be approximately 40% less than the dispersed-phase at the source, indicating that the measured values are reflecting the plume continuous-phase flow. Numerical simulations predict that the oily bubbles with diameters larger than 8 mm reach the surface with a small footprint, i.e. forming an oil slick origin, deflection of which with wind and surface current leads to the formation of an oil slick on the surface. Nineteen SAR images are used to estimate the oil seepage rate from GC600 for 2017 giving an average discharge of 14.4 cm³/s.
... Plusieurs études ont mesuré des vitesses d'émission de l'ordre du dixième de millimètre par seconde sur les dorsales lentes, et de l'ordre du centimètre par seconde sur les dorsales rapides (Di Iorio et al., 2005;Mittelstaedt et al., 2010;Ramondenc et al., 2006;Sarrazin et al., 2009;Schultz et al., 1992 ...
En bientôt quarante ans de recherche, de nombreuses connaissances ont été acquises sur la géologie des champs hydrothermaux, la chimie des fluides qui en réchappent et l’écologie des communautés qui les habitent. Celles-ci s’organisent en assemblages denses, distribués le long de la zone de dilution du fluide hydrothermal dans l’eau de mer, et dominés visuellement par une poignée d’espèces. La forte variabilité spatio-temporelle du fluide hydrothermal a une forte influence sur la distribution des communautés. Cependant, les mécanismes à l’origine de la réponse de la faune à cette variabilité sont peu compris. Pour cela, une approche modélisatrice est présentée. Les données collectées pendant plus de 20 ans sur l’édifice Tour Eiffel, sur le champ hydrothermal Lucky Strike (ride médio-Atlantique) ont été intégrées afin d’en extraire les composantes principales. L’étude intégrative des biomasses sur l’édifice montre que celles-ci sont largement dominées par la modiole Bathymodiolus azoricus. Ce bivalve est susceptible d’avoir une influence importante sur le fonctionnement de l’écosystème, et fait donc l’objet d’un premier modèle. La recherche de données pour le contraindre ont mené à mesurer des taux métaboliques in situ. Une fois le modèle paramétré, le modèle a fourni des estimations de flux encore inconnu. La simulation d’interruption du flux hydrothermal a fourni des indices sur la réponse de la modiole à la variabilité de son environnement.
... An alternative method, the acoustic scintillation from forward scattered signals, has been applied at the MEF [Xu and Di Iorio, 2011;Di Iorio et al., 2012] to monitor integrated plumes and investigate temporal variability in physical properties such as temperature or flow velocity. This method is based on recovering properties of the medium by measuring fluctuations of the acoustic signal passing through the plume [Di Iorio et al., 2005]. Using this method, Xu and Di Iorio [2011] estimated the heat transport of a plume 20 m above an orifice on Dante at the MEF as 62 MW. ...
We have designed, built, calibrated, and tested new anemometer and turbine flow meter devices to measure fluid velocity at high- and low-temperature focused and diffuse discharge sites at oceanic spreading centers. The devices perform at ocean floor depths and black smoker temperatures, and can be used to measure flow rates ranging over two orders of magnitude. Flow velocity is determined from the rotation rate of the rotor blades or paddle assembly. These devices have an open bearing design that eliminates clogging by particles or chemical precipitates as the fluid passes by the rotors. The devices are compact and lightweight enough for deployment from either an occupied or remotely operated submersible. The measured flow rates can be used in conjunction with vent temperature or geochemical measurements to obtain heat outputs or geochemical fluxes from both vent chimneys and diffuse flow regions. The devices have been tested on 30 Alvin dives on the Juan de Fuca Ridge and 3 Jason dives on the East Pacific Rise (EPR). We report 102 new measurements over a wide range of discharge temperatures (5° – 363°C), velocities (2 – 199 cm/s), and depths (1517 – 2511 m). These include the first advective heat output measurements at the High Rise vent field and the first direct fluid flow measurement at Middle Valley. Our data suggest that black smoker heat output at the Main Endeavor vent field may have declined since 1994 and that after the 2005–2006 eruption, the high=temperature advective flow at the EPR 9°50′N field may have become more channelized, predominately discharging through the Bio 9 structure. We also report first direct advective measurements in the Lau Basin and at the EPR 9°39.5′N with flow meters that predated devices described in this work and were used in the process of their development. We discuss potential error sources and how they may affect the accuracy of measurements by our and other devices. In particular, we use the turbulent plume theory to evaluate the effect of entrainment of ambient seawater.
... Underwater acoustics has been employed to acquire time-series measurements of the physical properties (e.g. flow rate, volume flux) of hydrothermal plumes in previous studies (e.g., DiIorio et al., 2005;Xu and DiIorio, 2012;Xu et al., 2013). In this paper, we report on a time-series measurement of hydrothermal heat flux acquired with the Cabled Observatory Vent Imaging Sonar (COVIS, Rona and Light, 2011;Xu et al., 2013), which is currently connected to the Endeavour node of the NEPTUNE observatory. ...
Continuous time-series observations are key to understanding the temporal evolution of a seafloor hydrothermal system and its interplay with thermal and chemical processes in the ocean and Earth interior. In this paper, we present a 26-month time series of the heat flux driving a hydrothermal plume on the Endeavour Segment of the Juan de Fuca Ridge obtained using the Cabled Observatory Vent Imaging Sonar (COVIS). Since 2010, COVIS has been connected to the North East Pacific Time-series Underwater Networked Experiment (NEPTUNE) observatory that provides power and real-time data transmission. The heat flux time series has a mean value of 18.10 MW and a standard deviation of 6.44 MW. The time series has no significant global trend, suggesting the hydrothermal heat source remained steady during the observation period. The steadiness of the hydrothermal heat source coincides with reduced seismic activity at Endeavour observed in the seismic data recorded by an ocean bottom seismometer from 2011 to 2013. Furthermore, first-order estimation of heat flux based on the temperature measurements made by the Benthic and Resistivity Sensors (BARS) at a neighboring vent also supports the steadiness of the hydrothermal heat source.
... [9] The self-contained (battery operated and internally logging) acoustic scintillation system was initially built in the early 1990s where it was first used to investigate hydrothermal vent flow from Hulk within the Main Endeavour Field in 1991 [Di Iorio et al., 2005]. Since then, the receiver was completely rebuilt incorporating digital signal processing boards, increased memory and a faster Thomson, IOS) is shown as CM* with the MEF location identified as a □. ...
The acoustic scintillation method is applied to the investigation and
monitoring of a vigorous hydrothermal plume from Dante within the Main
Endeavour vent field (MEF) in the Endeavour Ridge segment. A 40 day time
series of the plume's vertical velocity and temperature fluctuations
provides a unique opportunity to study deep sea plume dynamics in a
tidally varying horizontal cross flow. An integral plume model that
takes into account ambient stratification and horizontal cross flows is
established from the conservation equations of mass, momentum and
density deficit. Using a linear additive entrainment velocity in the
model (E = αUm + βU⊥) that is a
function of both the plume relative axial velocity (Um) and
the relative ambient flow perpendicular to the plume
(U⊥) gives consistent results to the experimental data,
suggesting entrainment coefficients α = 0.1 and β = 0.6. Also
from the integral model, the plume height in a horizontal cross flow
(Ua) is shown to scale as
1.8B1/3Ua-1/3N-2/3 for 0.01
≤ Ua ≤ 0.1 m/s where B is the initial buoyancy
transport and N is the ambient stratification, both of which are assumed
constant.
... [9] The self-contained (battery operated and internally logging) acoustic scintillation system was initially built in the early 1990s where it was first used to investigate hydrothermal vent flow from Hulk within the Main Endeavour Field in 1991 [Di Iorio et al., 2005]. Since then, the receiver was completely rebuilt incorporating digital signal processing boards, increased memory and a faster Thomson, IOS) is shown as CM* with the MEF location identified as a □. ...
The acoustic scintillation method has been used to study the vigorous
hydrothermal plume of Dante within the Main Endeavour vent field at the
Endeavour segment of the Juan de Fuca Ridge. Forty day time series of
vertical velocity and temperature fluctuations were obtained across the
rising plume at 20 m above the Dante edifice in an environment where the
flow is dominated by strong (5 cm s-1) semi-diurnal tidal
currents and a northerly mean residual flow (3 cm s-1). These
measurements provide a window on deep-sea hydrothermal plume dynamics in
strong oscillatory cross flows. Plume models that take into account
ambient stratification and time-dependent background flows, in
conjunction with these measurements, yield insights into entrainment,
plume bending, rise height, and, inferentially, mound heat flux. In
particular, an integral plume model with an entrainment velocity that is
a function of both the plume axial velocity and the ambient tidal flow
perpendicular to the plume axis indicates that increased entrainment
occurs during strong cross flows causing the plume to cool, rise more
slowly and bend. Results from a separate three-dimensional numerical
model show the plume bending with the tidal cycle and having rise
heights that vary from ~75 to ~250 m for an estimated mound heat flux of
40MW and a discharge salinity anomaly of -5 psu. The model attributes
the observed inverse relationship of plume vertical and background
horizontal velocities to the plume's bending by tidal currents as well.
... Underwater acoustics has been employed to acquire time-series measurements of the physical properties (e.g. flow rate, volume flux) of hydrothermal plumes in previous studies (e.g., DiIorio et al., 2005;Xu and DiIorio, 2012;Xu et al., 2013). In this paper, we report on a time-series measurement of hydrothermal heat flux acquired with the Cabled Observatory Vent Imaging Sonar (COVIS, Rona and Light, 2011;Xu et al., 2013), which is currently connected to the Endeavour node of the NEPTUNE observatory. ...
Initial acoustic monitoring of hydrothermal flow in the Main Endeavour
Field (MEF) captures the spatial distribution of diffuse and focused
discharge and shows potential for flux determinations. Our Cabled
Observatory Vent Imaging Sonar (COVIS) was connected to the NEPTUNE
Canada Endeavour Observatory in September 2010. Using a customized Reson
7125 multi-beam sonar, COVIS acquired a 29 day time series of black
smoker plume and associated diffuse hydrothermal flow from Grotto, a 30
m diameter vent cluster in the MEF, Juan de Fuca Ridge. Detection of the
spatial patterns of diffuse flow utilizes phase decorrelation of the
acoustic signal (200kHz) by buoyancy-driven turbulence (acoustic
scintillation) to produce a time series of maps. Substantial fluctuation
in the detected diffuse flow area (0.1 - 18 m^2) was observed over the
29 days of observation, although position remained stable. Acoustic
imaging of focused flow (400 kHz) utilizes high volume backscatter
(attributed to particles and turbulent sound speed fluctuations) to
image in 3D the initial tens of meters of rise of buoyant plumes.
Spectral analysis of bending inclination of a strong plume from multiple
fast smokers on the NW end of Grotto (north tower) indicates that the
dominant modes correspond with the ambient mixed semi-diurnal tide
(based on current meter data at a mooring 2.9 km to the north and on a
tidal model), with at least one secondary mode attributable to
sub-inertial flow related to inflow to the axial valley. A weaker plume
from several slower smokers is present on the NE end of Grotto. On first
analysis, the bending inclination of the weaker plume appears to be
affected by the stronger plume. Quantification of flow velocity and
volume flux of plumes begins with measuring the Doppler phase shift
through plume cross-sections beginning at 5 m above source vents where
discharge merges. The volume flux measurements enable calculation of
entrainment coefficients, which prior work on the same strong plume
indicated increase with degree of bending. The acoustic data in concert
with in situ measurements support inversions to obtain fluxes to
elucidate the role of hydrothermal flow in transfer of heat, chemicals
and biological material from the crust to the ocean. We are exploring
the feasibility of fitting plume models to Doppler velocity data in
order to estimate heat flux. Ongoing analysis pursues quantification of
fluid flux from diffuse and focused flow. In addition, the time series
provide observations of hydrothermal flow response to tidal, tectonic
and volcanic forcing on time scales from hours potentially to years.
(Work supported by NSF Grants Nos. OCE-0824612 and OCE-0825088)
... Underwater acoustics, owing to its non-intrusive and path-averaged characteristics, can be used to provide longterm , continuous monitoring of a hydrothermal system (). Acoustic scintillation and acoustic remote imaging are the two major active techniques that have been applied in many cases of hydrothermal investigation during the past two decades (Di Iorio et al., 2005; Rona et al., 1991; Rona et al., 2002; Rona et al., 2006). Acoustic scintillation refers to the phenomenon in which the modulation of the acoustic signal evolves in time and space due to the forward scattering caused by turbulence within the medium and is based on the theory of wave propagation through a random medium generalized by Tatarskii (1961); Ostashev (1997); Ishimaru (1978a). ...
... Variation of the effective refractive index (n eff ) is due to the fluctuation of current velocity and other passive properties like temperature and salinity. When applied to the investigation of hydrothermal vents, path-averaged plume properties like temperature variability and vertical flow are obtained (Di Iorio et al., 2005). However, suspended particles within the medium have been assumed to be negligible. ...
... A self-contained (battery operated and internally logging ) acoustic scintillation system as described by Di Iorio et al. (2005) was developed during early 1990. It was first used to investigate hydrothermal vent flow from Hulk within the Main Endeavor Field in 1991. ...
Acoustic methods are applied to the investigation and monitoring of a vigorous hydrothermal plume within the Main Endeavor vent field at the Endeavor segment of the Juan de Fuca Ridge. Forward propagation and scattering from suspended particulates using Rayleigh scattering theory is shown to be negligible (log-amplitude variance σ(χ) (2)~10(-7)) compared to turbulence induced by temperature fluctuations (σ(χ) (2)~0.1). The backscattering from turbulence is then quantified using the forward scattering derived turbulence level, which gives a volume backscattering strength of s(V)=6.5 × 10(-8) m(-1). The volume backscattering cross section from particulates can range from s(V)=3.3 × 10(-6) to 7.2 × 10(-10) m(-1) depending on the particle size. These results show that forward scatter acoustic methods in hydrothermal vent applications can be used to quantify turbulence and its effect on backscatter measurements, which can be a dominant factor depending on the particle size and its location within the plume.
... Backscatter acoustic techniques, which rely on the suspended particulate matter, are rapidly advancing to include plume imagery [9] and Doppler measurements of flow velocity [10] but have been limited to short temporal durations since measurements are made from underwater vehicles and submersibles. The acoustic scintillation method described here [11] is particularly advantageous to estimating simultaneously, vertical (buoyant) flow, horizontal (advective) flow, and temperature fluctuations at black smoker chimney vents or diffuse vent fields. Sound is propagated through the plume and is forward scattered by the turbulent refractive index properties of the flow. ...
An acoustical scintillation instrument is described that has been used to measure flow and temperature fluctuations at a hydrothermal vent plume. The vertical buoyancy driven flow together with the root-mean-square temperature fluctuations are obtained for vent structure 8F of the Main Endeavour vent field on the Endeavour segment of the Juan de Fuca Ridge. Long term (71 days) measurements are obtained and an estimate of the heat flux density which is of the order 0.06 MWm-2 is calculated. Measurements also show oscillations in the log-amplitude variance that result from either plume advection or increased entrainment of ambient fluids by the ambient tidal currents, thus demonstrating the need for a long time series measurement of simultaneous horizontal and vertical flow. Future measurements in the Main Endeavour vent field, with possible integration into the NEPTUNE seafloor observatory, will be over extended periods of time so that comparisons of these processes can be made with independent seismic data collected by NOAA/PMEL SOSUS array.
The relative importance of suspended particles and turbulence as backscattering mechanisms within a hydrothermal plume located on the Endeavour Segment of the Juan de Fuca Ridge is determined by comparing acoustic backscattermeasured by the Cabled Observatory Vent Imaging Sonar (COVIS) with model calculations based on in situ samples of particles suspended within the plume. Analysis of plume samples yields estimates of the mass concentration and size distribution of particles, which are used to quantify their contribution to acoustic backscatter. The result shows negligible effects of plume particles on acoustic backscatter within the initial 10-m rise of the plume. This suggests turbulence-inducedtemperaturefluctuations are the dominant backscattering mechanism within lower levels of the plume. Furthermore, inversion of the observed acoustic backscatter for the standard deviation of temperature within the plume yields a reasonable match with the in situ temperature measurements made by a conductivity-temperature-depth instrument. This finding shows that turbulence-inducedtemperaturefluctuations are the dominant backscattering mechanism and demonstrates the potential of using acoustic backscatter as a remote-sensing tool to measure the temperature variability within a hydrothermal plume.
