Plume Detection Research Articles

Sediment‐induced slope convection: Two‐dimensional numerical case studies

The potential role of sediment in oceanic slope convection is examined by means of a rotational numerical model applied in a vertical ocean slice. The model couples the hydrodynamics with transport, settling, deposition, and resuspension of fine‐grained silty muds. Sediment plumes (turbidity currents), descending on an idealized continental slope with constant bottom slope, are driven from an initial density anomaly caused by an assumed suspension of sediment in shelf water. A number of case studies were conducted in order to understand the effects of (1) different suspended sediment concentrations in shelf water as compared to an equivalent salinity anomaly (salt brine release), (2) different oceanic density stratifications, and (3) resuspension of bed sediment. It is demonstrated that sediment plumes may account for a downslope transport of water, which, once void of its sediment load, becomes lighter than water above. Then, sedimentation along the slope, with a maximum adjacent to the foot of the slope, drives vigorous upward convection (parameterized in the model), stirring slope water over a depth range of several hundred meters. This is in agreement with field observations from a tropical ocean. Detrainment associated with sediment settling constitutes an important mechanism inherent in sediment plumes. It not only induces upward convection but also prevents the rapid increase in plume thickness caused by entrainment as compared to “water mass plumes.” Owing to a balance between entrainment and detrainment, the sediment plume, while descending on the slope, attains constant height and bed shear velocities. In order to facilitate the detection of sediment plumes in (historical or future) field data, we describe their simulated traces in terms of water mass properties and flow anomalies.

Tunable Fabry–Perot etalon-based long-wavelength infrared imaging spectroradiometer

Imaging spectrometry enables passive, stand-off detection and analysis of the chemical composition of gas plumes and surfaces over wide geographic areas. We describe the use of a long-wavelength infrared imaging spectroradiometer, comprised of a low-order tunable Fabry-Perot etalon coupled to a HgCdTe detector array, to perform multispectral detection of chemical vapor plumes. The tunable Fabry-Perot etalon used in this research provides coverage of the 9.5-14-microm spectral region with a resolution of 7-9 cm(-1). The etalon-based imaging system provides the opportunity to image a scene at only those wavelengths needed for chemical species identification and quantification and thereby minimize the data volume necessary for selective species detection. We present initial results using a brassboard imaging system for stand-off detection and quantification of chemical vapor plumes against near-ambient-temperature backgrounds. These data show detection limits of 22 parts per million by volume times meter (ppmv x m) and 0.6 ppmv x m for dimethyl methyphosphonate and SF6, respectively, for a gas/background DeltaT of 6 K. The system noise-equivalent spectral radiance is approximately 2 microW cm(-2) sr(-1) microm(-1). Model calculations are presented comparing the measured sensitivity of the sensor to the anticipated signal levels for two chemical release scenarios.

A Review Of Environmental Applications Of Quasi-Stationary Electromagnetic Techniques

Electromagnetic (EM) techniques are the most commonly used geophysical methods in mineral exploration. However, the use of EM measurements for environmental and engineering applications like the detection of contaminant plumes or the exploration of waste sites is relatively new. The reason for the success of the application of EM methods to environmental problems lies in the variation of conductivity caused by different geometry of pore fluids and clay contents in rocks, and by the presence of organic and inorganic contaminants. Many EM methods/instruments used for mapping near surface geology exist and nowadays they play a central role in environmental geophysics. In general, these methods can be classified in two blocks: EM methods using a plane wave source of excitation and EM methods using a controlled source like a magnetic dipole or a loop source. The Very Low Frequency (VLF, VLF-R) and Radiomagnetotelluric (RMT) methods are chosen as representative methods for plane wave techniques, while horizontal loop EM methods operating in low induction numbers (EM31, EM34) and Transient Electromagnetic methods (TEM) are chosen as representatives of magnetic dipole or loop source techniques. Basic principles, advantages and disadvantages of each technique as well as their connection to specific environmental problems will be discussed. Different successful applications of these methods are reported in the literature. However, this review will focus on three major subjects: waste site exploration, detection of contaminated earth layers, and groundwater exploration. Case histories are presented illustrating the suitability of EM methods for solving such problems.

Detection of hydrothermal plumes on the northern Mid-Atlantic Ridge: results from optical measurements

Several water column surveys conducted on the northern Mid-Atlantic Ridge have been instrumental in the discovery of three new hydrothermal venting sites, and seven other active segments. Hydrothermal sources have yet to be pinpointed in six of these segments. In this study, the observed frequency of high-temperature venting from 23°N to 41°N on the Mid-Atlantic Ridge (MAR), a distance of approximately 1900 km, is one venting system per 150 km of ridge. Combining these data with those of other investigators for the region from 12°N to 41°N leads to an approximate venting frequency of one site per 90 km of ridge, although venting frequencies on sections of the MAR within this region are as high as one site per 25 km. To support this frequency of venting, and considering the larger dimensions of the MAR rift valley, the ratio of axial to off-axis heat loss must be higher on the MAR than on faster spreading ridges.

Detection of mantle plumes in the lower mantle by diffraction tomography: Hawaii

A new method is proposed to detect mantle plumes in the lower mantle. The method is akin to diffraction tomography, and relies on the scattering of long-period seismic body waves by nearly vertical heterogeneities. The theory is described in a companion paper [Ying Ji, H.-C. Nataf, Earth Planet. Sci. Lett., this issue]. Here we apply this method to an actual set of long-period digital seismograms recorded on the world-wide network of seismic stations between 1980 and 1994. We select seismograms that `illuminate' the lower mantle in a 20°×20° region around Hawaii. We construct an image of `plume-like' heterogeneities, using a cell size of 1°×1°, by a LSQR inversion of the scattered waves. This image shows a strong slow anomaly about 200 km northwest of Hawaii. Although the image is somewhat noisy, resolution tests indicate that this feature is fairly robust. The amplitude of the anomaly is between 30 and 60 times larger than what we predict from a simple thermal plume model, built with a 600 K maximum temperature excess, and a gaussian horizontal cross-section with an 1/ e diameter of 250 km. It is the first time that such a method is applied to the mantle. While we think that the existence of this anomaly is real, we do not know how to explain such a large amplitude. If real, this observation has a number of important geodynamical consequences. It indicates that a mantle plume is indeed responsible for the Hawaii hotspot, as speculated by Morgan [W.J. Morgan, Nature 230 (1971) 42–43]. The plume is nearly vertical. It originates from the D″ region, at the base of the lower mantle. The amplitude of the anomaly suggests that partial melt or/and a chemical anomaly must be present. The plume source is to the northwest of its surface expression, as predicted by some models of plume advection in the `mantle wind'.

Detection of mantle plumes in the lower mantle by diffraction tomography: theory

We investigate the properties of long-period seismic waves scattered by idealized plume conduits in the lower mantle. We build a schematic, yet realistic, model of the seismic velocity and density anomalies caused by a thermal plume. We devise a method to construct realistic seismograms of P-waves scattered by this anomaly. The results show that the scattered wave takes the form of an Airy phase, which arrives after the direct P-wave, at a time that corresponds to the shortest time it takes for the P-wave to travel from the source to the plume, and from there to the station. The predicted amplitude at a long period ( T≃20 s) is in the range of 1–5% of the amplitude of the direct wave. We explore the variation of the amplitude as a function of the geometrical parameters, and show that it is well explained by considering the contribution of the column of the plume in a T/4 Fresnel zone around the fastest scattered ray. We compare the amplitudes and waveforms obtained in the Rayleigh and Mie approximations, and find that, for realistic geometries, wider plumes yield a larger signal. Nevertheless, the predicted amplitudes are too small to yield a detectable signal. In the Born approximation, the image reconstruction of nearly vertical features reduces to a 2D linear inversion. We present a method, based on LSQR, to produce such images from the global set of long-period seismograms. In a companion paper [Ying Ji, H.-C. Nataf, Earth Planet. Sci. Lett., this issue], this method is applied to real data that sample the lower mantle beneath Hawaii.

Hydrothermal Plume Detection in the Deep Ocean—A Combination of Technologies

Hydrothermal Plume Detection in the Deep Ocean—A Combination of Technologies

An improved detection and characterization of active fires and smoke plumes in south-eastern Africa and Madagascar

The present study proposes improved multispectral methods for the detection of vegetation fires and smoke plumes that are applied to south-eastern Africa and Madagascar. Data are provided by the AVHRR sensor onboard the NOAA (11 and 14) satellites. Improvements of a multispectral methods address to fire detection difficulties arising from the low saturation level of AVHRR channel 3, from the presence of clouds and from contrasted vegetation and climate conditions. The methods are based on a multi-channel algorithm using AVHRR data, in visible and thermal ranges. Results are checked against other algorithm and ground concurrent data. It is shown that the presented multispectral methods are able to detect vegetation fires and associated smoke plumes with an improved accuracy. The results evidence clearly the seasonal character of biomass burning. Two maxima are characterized in the reference zone: one in September in Mozambique and the other in October in Eastern Madagascar. We note that fire intensity maxima were accompanied by well developed smoke plumes which could reach more than 50km.

Detection of hydrothermal plumes along the Southeast Indian Ridge near the Amsterdam‐St. Paul Plateau

A new self‐contained profiling instrument, attached to 91 lowerings of waxcores and dredges along a 1600 km stretch of the Southeast Indian Ridge, found six sites having optical back‐scatter anomalies indicative of hydrothermal plumes from high‐temperature seafloor venting. At five other sites, back‐scatter anomalies were less distinct, and at the remaining sites, anomalies were absent. These are the first documented hydrothermal sites along this intermediate‐rate spreading center and are among the very few yet discovered in the Indian Ocean basin. Some profiles exhibit complex back‐scatter anomalies suggestive of multiple sources of seafloor discharge. At one site, near‐bottom temperature anomalies of ∼0.1°C and the recovery of a vent‐specific barnacle provide the first precise seafloor location of active venting in the deep Indian Ocean. Although this study is only reconnaissance in nature, venting along this portion of the SEIR appears to be significantly less than predicted by global correlations of plume incidence as a function of spreading rate. Nevertheless, these sites may be important as biological connections between distinct faunal assemblages of Atlantic and Pacific vent fields.

Hydrothermal methane and manganese variation in the plume over the superfast-spreading southern East Pacific Rise

Onboard analyses of dissolved CH4 and Mn were conducted on the water column along the southern East Pacific Rise between 13 °50′ and 18°40′S during the 1993 RIDGE FLUX Cruise. Many hydrothermal plumes were identified by chemical anomalies which overlie more than half of the surveyed ridge crest. The CH 4/Mn ratio in the plumes shows wide variability ranges from about 0.05 to 3.9 due to wide range of CH 4 concentration. The CH 4-rich plumes were detected in the region of 16°00′—18°40′S where vigorous magmatic budget was confirmed by previous studies. Moreover, the CH 4/Mn ratio of the plumes is highly correlated with other volatile/metal parameters such as the S/Fe ratio in plume particulate. These results strongly suggest that volatile input caused by magmatic perturbation to hydrothermal systems is responsible for the CH 4/Mn variability in the southern EPR plumes, based on analogy of the case at the EPR 9°50′N site. The detection of several volatile-rich plumes and the extensive hydrothermal flux of volatile species are attributed to frequent magmatic events in the superfast spreading southern EPR.

Detection of Low-Latitude Plumes in the Outer Corona by [ITAL]Ulysses[/ITAL] Radio Ranging Measurements

Plumes have been detected beyond the field of view of coronagraphs in the range of 23-42 R(sub o) in an equatorial coronal hole by Ulysses radio ranging measurements conducted in 1991 at 13 and 3.6 cm wavelengths. These results show that plumes are not exclusive to polar regions, but appear to be intrinsic to open magnetic field regions at any latitude.

Monitoring Networks in Fractured Rocks: A Decision Analysis Approach

AbstractHydrogeological decision analysis is applied to the design of a performance monitoring network at a waste management facility overlying fractured bedrock. The objective of the monitoring system is to detect contaminants before they reach a regulatory compliance boundary in order to enable early and less costly on‐site remediation, and avoid the potentially more costly consequences of failure. Features in the design of the monitoring network include the number of monitoring wells to be installed and their locations, where in each borehole to position discrete monitoring zones, and how often to take water samples. The decision model identifies the preferred monitoring strategy as the design alternative, among all those considered, that minimizes the sum of the monitoring costs and the expected costs of failure and on‐site remediation. At a given distance from the facility, the highest probabilities of plume detection are obtained when the fractures intersecting the borehole wall that carry the largest flows are monitored. Monitoring intervals centered on fractures with highest aperture, or regions of highest fracture density, yield intermediate values, while intervals located at predetermined depths yield the lowest probabilities of detection. The monitoring scheme with the highest probability of detection is not necessarily the preferred monitoring strategy. For monitoring options that have a higher probability of detection than the preferred monitoring strategy, the higher expected cost of on‐site remediation, when combined with the increased cost of monitoring required to provide the higher probability of detection, can outweigh the reduction in the expected cost of failure brought about by a higher probability of detection. When the probability of contaminants migrating to the compliance boundary is small during the compliance period, changes in the probability of detection brought about by a more intense monitoring effort do not affect the expected cost of failure much; in these instances, the decision model may point to a reduced effort in performance monitoring.

Bias in Ground‐Water Data Caused by Well‐Bore Flow in Long‐Screen Wells

AbstractThe results of a field experiment comparing water‐quality constituents, specific conductance, geophysical measurements, and well‐bore hydraulics in two long‐screen wells and adjacent vertical clusters of short‐screen wells show bias in ground‐water data caused by well‐bore flow in long‐screen wells. The well screen acts as a conduit for vertical flow because it connects zones of different head and transmissivity, even in a relatively homogeneous, unconfined, sand and gravel aquifer where such zones are almost indistinguishable. Flow in the well bore redistributes water and solutes in the aquifer adjacent to the well, increasing the risk of bias in water‐quality samples, failure of plume detection, and cross‐contamination of the aquifer. At one site, downward flow from a contaminated zone redistributes solutes over the entire length of the long‐screen well. At another site, upward flow from an uncontaminated zone masks the presence of a road salt plume.Borehole induction logs, conducted in a fully penetrating short‐screen well, can provide a profile of solutes in the aquifer that is not attainable in long‐screen wells. In this study, the induction‐log profiles show close correlation with data from analyses of water‐quality samples from the short‐screen wells; however, both of these data sets differ markedly from the biased water‐quality samples from the long‐screen wells. Therefore, use of induction logs in fully cased wells for plume detection and accurate placement of short‐screen wells is a viable alternative to use of long screen wells for water‐quality sampling.

A study on the characteristics of groundwater contamination of the Nanji landfill and its surrounding hydrogeologic system

Abstract The Nanji landfill causes a serious adverse affect to nearby groundwater and surface water systems due to that it has been constructed on the very permeable and valnerable sand and gravel deposit without installing any pollution control systems such as top cap, bottom liner, and leachate collection system. A comprehensive rededial investigation including exploratory boring, plume detection, and site‐characterization was performed to provide the basic data for the design of the remeadial measures. As a part of the investigation, this study was conducted using 10 numbers of existing monitoring wells and a bundle type well to determine the contaminant indicators for the plume detection and to define the vertical and horizontal variations of specific contaminants via distances from the landfill. The results clearly show that EC and temperature were a good pollution indicators and the vertical variation of specific contaminants measured in the fully screened well were 20 to 90% more than those measured at same depth in bundle type well located just 2m apart. This paper present a cost‐effective monitoring and sampling method to define the contaminant plume and provide a basic data for remedial actions.

Hydrothermal exploration near the Azores Triple Junction: tectonic control of venting at slow-spreading ridges?

Simultaneous acoustic imaging of the seafloor and detection of particle-rich plumes in the overlying water column have been used to identify and determine the tectonic setting of high-temperature ‘black smoker’ hydrothermal activity along 200 km of the Mid-Atlantic Ridge between 36° and 38°N. Using this approach, we have identified hydrothermal signals at 7 different locations. These results indicate a higher incidence of hydrothermal activity along this section of ridge axis than has been reported elsewhere along slow spreading ridges. Our data show that the majority of hydrothermal sites here are located near to non-transform offsets rather than at the centres of individual ridge segments. We suggest that this intersection of fabrics, associated with ridge discontinuities and the spreading process, is instrumental in focussing hydrothermal flow at these localities. Future strategies of exploration for hydrothermal activity on slow-spreading ridges may need to be revised accordingly.

5408182 Facility and method for the detection and monitoring of plumes below a waste containment site with radiowave tomography scattering methods: Stolarczyk Larry G; Mondt William E Raton, NM, United States Assigned to Rim Tech Inc

5408182 Facility and method for the detection and monitoring of plumes below a waste containment site with radiowave tomography scattering methods: Stolarczyk Larry G; Mondt William E Raton, NM, United States Assigned to Rim Tech Inc

CO_2 laser-based differential absorption lidar system for range-resolved and long-range detection of chemical vapor plumes

A dual CO(2) laser-based differential absorption lidar (DIAL) system has been constructed and demonstrated for range-resolved mapping of chemical vapor plumes. The system acquires high range resolution through the use of plasma-shutter pulse clippers that extinguish the nitrogen tail of the CO(2)-laser output. Aprogrammable servomotor-driven scanner allows full hemispherical coverage of the interrogated field. A high-speed direct-detection receiver subsystem is used to gather, process, and display vapor-concentration data in near real time. Data demonstrating range-resolved detection of low concentrations of chemical plumes from ranges of 1 to 2 km are presented. In the column-content detection mode, trace levels of secondary vapors from various organophosphate liquids were monitored. Detection of an SF(6) vapor plume released 16 km from the DIAL system is also adduced.

In situ observations in aircraft exhaust plumes in the lower stratosphere at midlatitudes

Instrumentation on the NASA ER‐2 high‐altitude aircraft has been used to observe engine exhaust from the same aircraft while operating in the lower stratosphere. Encounters with the exhaust plume occurred approximately 10 min after emission with spatial scales near 2 km and durations of up to 10 s. Measurements include total reactive nitrogen, NOy, the component species NO and NO2, CO2, H2O, CO, N2O, condensation nuclei, and meteorological parameters. The integrated amounts of CO2 and H2O during the encounters are consistent with the stoichiometry of fuel combustion (1:1 molar). Emission indices (EI) for NOx (=NO + NO2), CO, and N2O are calculated using simultaneous measurements of CO2. EI values for NOx near 4 g (kg fuel)−1 are in good agreement with values scaled from limited ground‐based tests of the ER‐2 engine. Non‐NOx species comprise less than about 20% of emitted reactive nitrogen, consistent with model evaluations. In addition to demonstrating the feasibility of aircraft plume detection, these results increase confidence in the projection of emissions from current and proposed supersonic aircraft fleets and hence in the assessment of potential long‐term changes in the atmosphere.

Regional-scale ground water quality monitoring via integer programming

A network design approach developed in this paper identifies monitoring sites in multi-layered, regional ground water flow systems at risk of contamination from waste storage facilities. Candidate locations are assigned weights that quantify monitoring value in terms of the prospect of plume detection and exposure hazard criteria. Detection criteria are based on the location of a site with respect to the source of contamination and potential contaminant plumes. Exposure criteria are based on the size of the population that consumes water from a supply well and the distances between the supply well and probable zones of contamination. The weights are used in a binary integer mathematical programming problem which selects the monitoring locations. On a 100-point rating scale developed to quantify composite plume detection and characterization efficiency, the network design model scored 87, compared with a score of 76 for a pre-existing monitoring network. (The model and pre-existing schemes involve the same number of wells.) The model selects well sites that are close together near the source of contamination, facilitating early detection of a contaminant release, and further apart downgradient, resulting in areal coverage for plume characterization.

Hazardous wastes assessment, management, and minimization

Hazardous wastes assessment, management, and minimization