scholarly journals Technical note: Efficient imaging of hydrological units below lakes and fjords with a floating, transient electromagnetic system (FloaTEM)

2021 ◽  
Author(s):  
Pradip Kumar Maurya ◽  
Frederik Ersted Christensen ◽  
M. Andy Kass ◽  
Jesper Bjergsted Pedersen ◽  
Rasmus Rumph Frederiksen ◽  
...  
Keyword(s):  
Water Column ◽  
Saline Water ◽  
Technical Note ◽  
Water Bodies ◽  
Aquatic Environments ◽  
Electromagnetic System ◽  
Transient Electromagnetic ◽  
Sediment Types ◽  
Imaging Results ◽  
Depth Of Investigation

Abstract. Imagining geological layers beneath lakes, rivers, and shallow seawater provides detailed information critical for hydrological modelling, geologic studies, contaminant mapping, and more. However, significant engineering and interpretation challenges have limited the applications, preventing widespread adoption in aquatic environments. We have developed a towed transient electromagnetic (tTEM) system to a new, easily configurable floating, transient electromagnetic instrument (FloaTEM) capable of imaging the subsurface beneath both fresh and saltwater water bodies. Based on the terrestrial tTEM instrument, the FloaTEM system utilizes a similar philosophy of a lightweight towed transmitter with a trailing, offset receiver, pulled by a small boat. The FloaTEM system is tailored to the specific fresh or saltwater application as necessary, allowing investigations down to 100 m in freshwater environments, and up to 20 m on saline waters. Through synthetic analysis we show how the depth of investigation of the FloaTEM system greatly depends on the resistivity and thickness of the water column. The system has been successfully deployed in Denmark for a variety of hydrologic investigations, improving the ability to understand and model processes beneath water bodies. We present two freshwater applications and a saltwater application. Imaging results reveal significant heterogeneities in the sediment types below the freshwater lakes. The saline water example demonstrates that the system is capable to identify and distinguish clay and sand layers below the saline water column.

scholarly journals How many species of cladocerans (Crustacea, Branchiopoda) are found in Brazilian Federal District?

2013 ◽  
Vol 24 (4) ◽  
pp. 351-362 ◽  
Author(s):  
Francisco Diogo Rocha Sousa ◽  
Lourdes Maria Abdu Elmoor-Loureiro
Keyword(s):  
Urban Areas ◽  
Aquatic Vegetation ◽  
Federal District ◽  
Water Bodies ◽  
Aquatic Environments ◽  
Number Of Species ◽  
Different Types ◽  
Local Extinctions ◽  
Richness Estimators ◽  
Selection Of

AIM: This study aimed provides a checklist of cladocerans and also an evaluation of richness and species composition in the Federal District, Brazil. METHODS: Checklist of cladocerans was obtained evaluating data from the literature, from taxonomic collection (Elmoor-Loureiro's collection) and from fauna surveys conducted over more than three decades in different types of aquatic environments. RESULTS: The 57 water bodies studied showed 56 species, of which 14 are new records. The number of species contained in the list displayed corresponds to 85% of what was expected for richness estimators. The highest number of species was observed in the lentic water bodies (52), which also presented the specific composition of fauna (R = 0.110; p = 0.016), possibly because there were samples taken among the aquatic vegetation. According to our understanding, some species may be subject to local extinctions because they inhabit water bodies located exclusively in urban areas, which can lead to a decline in richness. CONCLUSION: Thus, the results of this study can assist in monitoring aquatic environments and in selection of new areas for surveys of cladocerans in the Federal District.

Rapid Mapping of Hydrological Systems in Tanzania Using a Towed Transient Electromagnetic System

Ground Water ◽  
2021 ◽  
Author(s):  
Denys Grombacher ◽  
Pradip Kumar Maurya ◽  
Johan Christensen Lind ◽  
John Lane ◽  
Esben Auken
Keyword(s):  
Electromagnetic System ◽  
Rapid Mapping ◽  
Transient Electromagnetic

The Physical Environment of Lakes

2003 ◽  
Author(s):  
Andrew S. Cohen
Keyword(s):  
Water Column ◽  
Hydrological Cycle ◽  
Biological Information ◽  
Lake Basin ◽  
Physical Processes ◽  
Sediment Types ◽  
Short Time Span ◽  
Heat Penetration ◽  
Short Time ◽  
Inputs And Outputs

Before discussing paleolimnological archives, we need to consider those aspects of limnology that regulate how information is produced, transmitted, and filtered through the water column. Although many limnological processes leave behind sedimentary clues of their existence or intensity and are thus amenable to paleolimnological analysis, others leave little or no detectable trace. Our consideration of limnology here emphasizes the former. Throughout the next three chapters we will examine the properties of lakes, the implications of these properties for paleolimnology, and the types of physical, chemical, and biological information that can be transcribed into sedimentary archives. Physical processes in lakes are of interest because they act as intermediary hydroclimate filters between external forcing events of interest, like climate, and the paleolimnological record. For example, understanding the hydrology of a lake is important because water inputs and outputs, which are often controlled by climate, determine lake levels, which in turn are recorded by ancient shoreline elevations, or indirectly by salinity indicators. Light and heat penetration regulate the distribution of organisms and the mixing of the water column, recorded by the distribution of various fossils, sediment types, and geochemical characteristics of sediments. Also, current and wave activity affect the transport of sedimentary particles and therefore the distribution of sediment types around a lake basin. Understanding these physical processes therefore provides us with a means of linking sedimentological, geochemical, and paleobiological records of lake deposits to the external environment. Water enters and exits lakes through a variety of paths that comprise part of the earth’s hydrological cycle. The lake components of this cycle include a series of inputs and outputs of water, which in combination with the morphometry of the lake basin, collectively determine the lake’s level. Inputs include precipitation, surface runoff from rivers, and groundwater discharge into the lake. Outflows include surface outflow, evaporation, evapotranspiration losses from emergent aquatic plants, groundwater recharge, and hydration reactions with underlying sediments. If water inputs and outputs for a lake are equal over a short time span, the lake surface elevation will remain constant. This is approximately the case in most lakes that are surficially open basins.

Drone-borne transient electromagnetic system and its application in UXO detection

2018 ◽  
Author(s):  
Zhi-peng Qi ◽  
Xiu Li ◽  
He Li ◽  
Ying-ying Zhang ◽  
Jianmei Zhou
Keyword(s):  
Electromagnetic System ◽  
Transient Electromagnetic

scholarly journals Quantitative estimations of aquifer properties from resistivity in the Bolivian highlands

2019 ◽  
Vol 2 (1) ◽  
pp. 113-124
Author(s):  
Etzar Gómez ◽  
Viktor Broman ◽  
Torleif Dahlin ◽  
Gerhard Barmen ◽  
Jan-Erik Rosberg
Keyword(s):  
Hydraulic Conductivity ◽  
Saline Water ◽  
Cost Effective ◽  
Unconsolidated Sediments ◽  
Aquifer System ◽  
Transient Electromagnetic ◽  
Rock Formations ◽  
Hydrogeological Characteristics ◽  
Electrical Soundings ◽  
Available Information

Abstract Resistivity data constitute the largest part of the available information to assess the hydrogeological characteristics of the aquifer system near Oruro, in the central part of the Bolivian Altiplano. Two aquifers are part of this system; top unconsolidated sediments storing fresh water in their granular voids, overlying fractured hard rock formations where saline water was detected in connection to some faults. This study proposes an indirect and cost-effective way to estimate aquifer hydraulic properties for the groundwater management in the region. Hydraulic conductivity and transmissivity in the top aquifer were estimated using an empirical linear relationship between hydraulic conductivity and resistivity. This latter parameter, as well as the aquifer thickness, were obtained from the inverted models corresponding to the geoelectrical tests performed in the study area (electrical resistivity tomography, transient electromagnetic soundings and vertical electrical soundings). The highest estimated transmissivity values are ∼4.0 × 10−2 m2/s located in the centre of the study area, the lowest values are ∼3.4 × 10−3 m2/s, located around thermal intrusions to the south and where the top of the bedrock is shallow (∼20 m depth) to the west. The methodology presented in this study makes wider use of resistivity measurements to identify promising groundwater production sites.

Reducing Motion-Induced Noise With Mechanically Resonant Coil Sensor in a Rigid Helicopter Transient Electromagnetic System

2020 ◽  
Vol 67 (3) ◽  
pp. 2391-2401
Author(s):  
Fei Liu ◽  
Jun Lin ◽  
Yanzhang Wang ◽  
Shilong Wang ◽  
Quan Xu ◽  
...  
Keyword(s):  
Electromagnetic System ◽  
Transient Electromagnetic

scholarly journals Characterisation of subglacial water using a constrained transdimensional Bayesian transient electromagnetic inversion

Solid Earth ◽  
2020 ◽  
Vol 11 (1) ◽  
pp. 75-94 ◽  
Author(s):  
Siobhan F. Killingbeck ◽  
Adam D. Booth ◽  
Philip W. Livermore ◽  
C. Richard Bates ◽  
Landis J. West
Keyword(s):  
Electrical Resistivity ◽  
Saline Water ◽  
Radar Data ◽  
High Resistivity ◽  
Transient Time ◽  
Fractured Bedrock ◽  
Transient Electromagnetic ◽  
Seismic Shear ◽  
Time Domain Electromagnetic ◽  
Ground Penetrating

Abstract. Subglacial water modulates glacier-bed friction and therefore is of fundamental importance when characterising the dynamics of ice masses. The state of subglacial pore water, whether liquid or frozen, is associated with differences in electrical resistivity that span several orders of magnitude; hence, liquid water can be inferred from electrical resistivity depth profiles. Such profiles can be obtained from inversions of transient (time-domain) electromagnetic (TEM) soundings, but these are often non-unique. Here, we adapt an existing Bayesian transdimensional algorithm (Multimodal Layered Transdimensional Inversion – MuLTI) to the inversion of TEM data using independent depth constraints to provide statistical properties and uncertainty analysis of the resistivity profile with depth. The method was applied to ground-based TEM data acquired on the terminus of the Norwegian glacier, Midtdalsbreen, with depth constraints provided by co-located ground-penetrating radar data. Our inversion shows that the glacier bed is directly underlain by material of resistivity 102 Ωm ± 1000 %, with thickness 5–40 m, in turn underlain by a highly conductive basement (100 Ωm ± 15 %). High-resistivity material, 5×104 Ωm ± 25 %, exists at the front of the glacier. All uncertainties are defined by the interquartile range of the posterior resistivity distribution. Combining these resistivity profiles with those from co-located seismic shear-wave velocity inversions to further reduce ambiguity in the hydrogeological interpretation of the subsurface, we propose a new 3-D interpretation in which the Midtdalsbreen subglacial material is partitioned into partially frozen sediment, frozen sediment/permafrost and weathered/fractured bedrock with saline water.

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