Displays

Geophones are essential for monitoring seismic activity to study the structure of the earth for ground surveys, mineral exploration and early warning detection of geo-hazards. Traditional electromagnetic based geophones are fairly effective in detecting micro-seismic activity and ambient signals. Their induction based mass-spring sensing mechanism can however be somewhat performance limiting. Limitations include reduced frequency response, resolution and recovery times between successive activities. This ultimately impacts the sensitivity and performance of the device. In this paper, we present a novel optical fiber geophone sensor that addresses these issues through superior sensitivity, performance and ease of deployment. Our optical fiber geophone is polarization based, single ended and operates on a Michelson interferometric principle. Tests were performed to compare the performance of our optical fibre geophone to that of a commercial electromagnetic geophone. Vibrations of varying magnitude were remotely generated at 1.065 m from both devices. Sensor signal responses to disturbances of energy lower than 1.1 mJ were plotted and analysed. Observed traces from the sensor responses were compared, showing that the fiber geophone has significantly shorter response and recovery times. As a result, the resolution between rapidly succeeding signals is considerably greater for the optical fiber geophone. Sensitivity plots of the amplitude response to the vibration energy gave a scatter of points depicting a higher degree of precision and accuracy for the fiber geophone. Response slopes of 11.70 a.u/mJ and 10.31 a.u/mJ respectively were obtained for the sensitivity of the optical fiber geophone versus the electromagnetic geophone. While the typical spurious frequency is close to 150 Hz for the traditional geophone, the bandwidth of the optical fiber geophone is an order of magnitude greater.

Keywords- Geophone, Optical fibre, Polarisation, Michelson Interferometer

How to cite: Jena, J., Wassin, S., Bezuidenhout, L., Doucouré, M., and Gibbon, T.: Polarisation Based Interferometric Optical Fibre Geophone Sensor Designed for High Resolution Seismic Detection, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4991, https://doi.org/10.5194/egusphere-egu2020-4991, 2020.

The chemical, mineralogical and textural investigation of drill cores demands objective and repeatable information unaffected by the human bias to be able to correlate significant features across drillcores. Imaging Laser induced Breakdown Spektroscopy (LIBS) can be applied to large scales at high spatial resolution in relatively short times to obtain detailed chemical, mineralogical and textural information with a minimum of sample preparation. The application of the Spectral Angle Mapper (SAM) algorithm for supervised classification of the LIBS hyperspectral data cubes provides a relatively fast, but easy to handle tool to visualize and quantify variations in the chemical, mineralogical composition of complex ores from the sub-millimetre to the metre scale. The information derived offers novel and barely investigated interpretation opportunities in a very detailed manner which directly can be used for exploration purposes. The investigated Merensky Reef is about 1 m thick. It consists of pegmatoidal pyroxenite framed by the lower and upper thin chromitite seams. The Merensky Reef is one major ore body out of three for platinum-group elements (PGE) within the Bushveld Igneous Complex which is the world’s largest known layered intrusion and largest PGE resource on Earth   Detailed LIBS-based imaging measurements with 200µm spotsize were accompanied by space-resolved reference measurements based on SEM/MLA (4µm) and µ-EDXRF (20µm), as well as bulk chemical analyses for multiple core slices. The SAM algorithm was applied for classification of hyperspectral LIBS images as being sensitive for differences in mineral chemistry. Focus was put on the pre-processing of LIBS spectra prior to SAM classification, on the development of the spectral library, and on the validation of the classified data. The SAM classification algorithm, which is solely based on ratios between spectral intensities, was found insensitive to normal shot-to-shot plasma variations and to chemically induced matrix effects. However, the algorithm may become inaccurate at low signal to noise ratios, at the border between different mineral grains (mixed spectra), or when classifying chemically similar phases such as pyrite and pyrrhotite. The extent of mixed spectra depends both on the size of the mineral grains as well as on the spot size of the LIBS laser. The SAM algorithm was successfully applied for classification of several base metal sulphides, rock-forming minerals, accessory minerals, as well as several mixed phases representing the main borders between different mineral grains. The obtained classified LIBS image images the spatial distribution of the different phases, which corresponds very well to the reference measurements based on highly space-resolved  EDXRF and SEM/MLA mineral distribution maps. The investigated core piece highlights the extremely heterogeneous distribution of e.g. the sulphide phases. The LIBS-SAM classification image was used to estimate metal concentrations based on point counting. The applicability has been explored for Cu, Ni, S, and Cr. This approach, when applied on sufficiently large surfaces, enables quantification of well-defined mineral phases, as well as the possible detection of trace elements (e.g. Pt, Pd) that occur in very small nuggets.

How to cite: Rammlmair, D. and Meima, J.: Quantitative mineralogy of chromite ore based on imaging Laser Induced Breakdown Spectroscopy and Spectral Angle Mapper Classification Algorithm, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19373, https://doi.org/10.5194/egusphere-egu2020-19373, 2020.

In terms of terrestrial animal communication, elephants are especially noteworthy because they have been documented to produce some of the loudest sounds at frequencies between 10-35 Hz. Their vocalisations, or ‘rumbles’, with fundamental frequencies in the infrasonic range (≤ 20 Hz) can have amplitudes as high as 117 dB. Here we present our efforts to evaluate the performance of the Raspberry Shake and Boom, a low-cost seismic and acoustic sensor, for identifying and monitoring the movements of African Bush Elephants (Loxodonta africana). The test area was the Adventures with Elephants elephant reserve in South Africa which includes a herd of 7 elephants (3 females, 2 males, and 2 juveniles). Within the reserve we deployed a local network of 5 Raspberry Shake and Boom units in October 2019 in order to record seismo-acoustic waves generated by the herd. The network also included other seismic and acoustic sensors of different sensitivities which were used to assess the performance Raspberry Shake and Boom units. We show that the Raspberry Shake and Boom units performed well during the deployment, with clear recordings of elephant movement and rumbles. The acoustic data also suggests that we may be able to discriminate between individual elephants due to the distinct frequencies of their rumbles. This presentation will provide general information on the potential use of low-cost sensor units for the purpose of unobtrusively monitoring vulnerable wildlife such as elephants.

How to cite: Lamb, O., Shore, M., Lees, J., and Lee, S.: Monitoring African Bush Elephants with the OSOP Raspberry Shake and Boom, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1503, https://doi.org/10.5194/egusphere-egu2020-1503, 2020.

I will expose some possibilities regarding the use of metallic probes of different lengths in GPR and TDR prospecting. With regard to GPR, multi-length probes are dipole-like antennas whose length can be changed by means of switches. The switches can be implemented with PIN diodes, and can act as electronic “knifes”. Therefore, they allow to cut (switched off) or prolong (switched on) the branches of a couple of antennas, and this allows to have more couples of equivalent antennas making use of a unique physical couple of antennas. This allows to contain the size of the system. In particular, a reconfigurable prototypal stepped frequency GPR system was developed within the project AITECH (http://www.aitechnet.com/ibam.html)  and was tested in several cases histories  [1-3]. Within this reconfigurable GPR, it is also possible to reconfigure vs. the frequency the integration times of the harmonic tones constituting the radiated signal. This feature allows to reject external electromagnetic interferences without filtering the spectrum of the received signal [4] and without increasing the radiated power.

With regard to TDR measurements, a multi-length probe consists of a TDR device where the rods (in multi-wire version) or the length of internal and external conductor (in coaxial version) can be changed. This can be useful for the measurements of electromagnetic characteristics of a material under test (MUT), in particular its dielectric permittivity and magnetic permeability, both meant in general as complex quantities. Multi-length TDR measurements allow to acquire independent information on the MUT even at single frequency, and this can be of interest in the case of dispersive materials [5-6].

Acknowledgements

I collaborated with several colleagues about the above issues. To list of them would be long, so I will just mention their affiliations: Florence Engineering srl, University of Florence, IDSGeoradar srl, 3d-radar Ltd, Institute for Archaeological and Monumental Heritage IBAM-CNR, University of Bari, University of Malta. Finally, a particular mention is deserved for the Cost Action TU1208.

References

[1] R. Persico, M. Ciminale, L. Matera, A new reconfigurable stepped frequency GPR system, possibilities and issues; applications to two different Cultural Heritage Resources, Near Surface Geophysics, 12, 793-801, 2014.

[2] L. Matera, M. Noviello, M. Ciminale, R. Persico, Integration of multisensor data: an experiment in the archaeological park of Egnazia (Apulia, Southern Italy), Near Surface Geophysics, 13, 613-621, 2015.

[3] R. Persico, S. D'Amico, L. Matera, E. Colica, C. De, Giorgio, A. Alescio, C. Sammut and P. Galea, P. (2019), GPR Investigations at St John's Co‐Cathedral in Valletta, Near Surface Geophysics, 17, 213-229, 2019.

[4] R. Persico, D. Dei, F. Parrini, L. Matera, Mitigation of narrow band interferences by means of a reconfigurable stepped frequency GPR system, Radio Science, 51, 2016.

[5] R. Persico, M. Pieraccini, Measurement of dielectric and magnetic properties of Materials by means of a TDR probe, Near Surface Geophysics, 16,1-9, 2018.

[6] R. Persico, I. Farhat, L. Farrugia, S. d’Amico, C. Sammut, An innovative use of TDR probes: First numerical validations with a coaxial cable, Journal of Environmental & Engineering Geophysics, 23, 437-442, 2018.

How to cite: Persico, R.: Multi-length probes in GPR and TDR data, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7426, https://doi.org/10.5194/egusphere-egu2020-7426, 2020.

Assessment of a power lines condition is an important task for all countries. It includes GPS mapping of the: 1) wire breaks; 2) places of the increased current leakage, for example corona detection; 3) degree of wires sagging between power line towers; 4) location and conditions of the power line towers; 5) vegetation encroachment along a power line corridor.  Considering that power line currents, including leakage currents, create strong magnetic field, use of magnetometers in the range from DC to sound frequencies for the solution of tasks 1-4 is highly prospective. At the same time, it is possible the control of the vegetation critical proximity to a power line adjacent zone by the increased leakage current (threats of the increased leakage current or breakdown to a tree crown). Thus the task 5 also can be solved.

The goal of the present report is to introduce the new design of miniature low-weight three-component sensor for measurement of alternative vector magnetic field onboard UAV – induction magnetometer (IM) - with autonomous system including two-component tiltmeter and GPS antenna inside in order to obtain precise measurement timing, UAV coordinates and altitude during movement. These data are stored in the SD memory card. Construction details, tests results and technical specifications of this IM for are presented.

How to cite: Korepanov, V., Pronenko, V., Dudkin, F., and Prystai, A.: Induction Magnetometer transported by UAV for power lines monitoring, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7227, https://doi.org/10.5194/egusphere-egu2020-7227, 2020.

This work is presenting the attenuation of coda waves in the Rif region. Using 15 broadband stations, we investigate the attenuation of coda waves utilizing the single backscattering model of aki and chouet. We collect 70 local earthquakes during 2014 for five laps time window 20, 30, 40, 50 and 60s. We computed the quality factors at different central frequencies band on which start from 1.5, 3.0, 6.0, 9.0, 12.0 and 18.0 Hz. For 40s window length, the Qc gives average value for the whole zone of about 128,51 for 1.5 Hz and 993,44 for 18 Hz band frequencies. We observed a clear dependency between the quality factor and the frequency. Also, we have found that this region is tectonic active comparing to previous studies around the world.

How to cite: Arab, O., harnafi, M., ouchen, I., azguet, R., El Fellah, Y., and Jamal, S.: The attenuation of coda waves in the RIF area., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4885, https://doi.org/10.5194/egusphere-egu2020-4885, 2020.

Submarine groundwater discharge (SGD) is any direct flow of fluid across the seafloor, which forms bubbly or leaky springs and seeps from the intertidal zone to the deep sea. SGDs can significantly alter physico-chemical conditions of seepage zones. Identifying and mapping SGD is crucial to further recognize its influence in both marine and terrestrial ecosystems. However, mapping this phenomenon has been a continuing challenge, mainly due to the difficulty in its detection and quantification. This study explores the capability and applicability of an inexpensive, commercially available, recreational-grade combination of depth meter and side scan sonar system to image different types and identify point sources of coastal SGDs. Standard and systematic methodologies for efficient imaging and processing were established. The utility of the recreational-grade system was assessed and validated using a research-grade side scan sonar. SCUBA diving and CTD casting were conducted for ground-truthing and further characterization. Lower frequency sonars (83/200 kHz) showed more distinct acoustic signatures of discrete and dispersed bubbly SGDs, than the higher frequency system (455 kHz and 780 kHz research-grade unit). Sonar images showed that SGD plumes can be indicated by near seafloor to midwater cloud-like features. Spring-type SGDs tend to form cloud features with a funnel-shaped morphology. In sites where SGDs are dispersed, the acoustic signature is a curtain-like cloud, with higher bubble density in the upper water column. This is consistent with diver-based observation of increasing bubble sizes (<1 mm to ~30 mm) from point source to water surface. CTD casts indicate that the SGDs have recirculated seawater, with increasing temperature and salinity with depth. In the assessment of system and data processing requirements, and costing, a recreational-grade unit provides a good alternative for coastal SGD works.

How to cite: Gabuyo, M. R., Siringan, F., Sarmiento, K. J., and Flores, P. C.: Cost-effective recreational-grade single beam echosounder with side scan sonar system in imaging bubbly coastal submarine groundwater discharge, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-407, https://doi.org/10.5194/egusphere-egu2020-407, 2020.

Absorption muon imaging is a technique that can measure density variations underground down to a few hundred meters. Then, it can prove to be useful in a mining environment: to help assess the ore bodies volumes and/or to monitor the underground for natural hazards that can happen at the surface because of the mining exploitation. Here we report the result of an experiment designed to test the capabilities and resolution power of a cosmic muon measurement in a mining environment compared to other standard geophysics tools: gravimetry and seismic studies. It consists of three independent measurement of a subset of the decommissioned iron mine of May-sur-Orne (France). The first one was made using a 50x50cm² micromegas based muon telescope installed at the deepest non-submerged level (50m underground) during 3 months. The second one is a gravimetry survey of the surface area inside the muon telescope acceptance cone. And the third one is a study of refracted and reflected seismic waves along a single line above the muon telescope location. The investigation volume was chosen because of the presence of surface risks (neighborhood), the unknown of some uncharted volume and the presence of an ore storage volume of several meter cubed that was used during the mine exploitation and which filling state is unknown.

The data analysis showed that while muon tomography is able to detect the negative density anomaly of the storage volume, the gravimetry measurement is not sensible to it. However, the seismic study was able to detect the volume as well and its location and extension is compatible with the muon measurement.

How to cite: Bouteille, S., Bitri, A., Dietz, M., and Gance, J.: Benchmark of multiple geophysics tools to study the voids in the upper levels of a decommissioned iron mine, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21715, https://doi.org/10.5194/egusphere-egu2020-21715, 2020.

The low cost seismograph under study consists of low cost open source hardware and software microprocessor boards (Arduino Uno R3  and Raspberry Pi 3 B+ ), customized low noise design signal amplifiers, low power dissipation sophisticated power supply, two (2) kinds of earth ground shaking sensors a) Ceramic Accelerometer with cutoff frequency fc=0.15Hz and b) moving coil geophone with cutoff frequency fc=4.5Hz. The signals from the two sensors are amplified independently, while an active second order low-pass anti-alias filter and an 8th order active low-pass anti-alias filter have been used. Finally, a low-cost microprocessor board is responsible for digitizing the analog data from the amplified signal of the sensors with a frequency sampling rate of 345Hz. The aim of the present work is to design and test a systemic protocol in order to evaluate the performance of the proposed low cost seismograph for monitoring local to regional seismicity and micro seismicity. The proposed low-cost system was installed in an area of high seismic activity (Lefkada Island – Village Evgiros) and the recordings are transmitted to the database continuously from the day of its installation up today. Thus have create an amount of data for more than 280 days and all of those data have been stored to our database. Collocated with a high resolution 24 bits digitizer equipped with a broad band seismometer give us the opportunity to compare the recordings. To this end, a testing list of 15 local events has been created with different epicenters and magnitudes. For each event the recording signals have been analyzed in terms of a) power spectrum analysis, b) estimation of first arrival times of both P and S waves, c) signal amplitudes and d) earthquake duration. The choice of those specific measures was done in order to evaluate the performance of the low-cost seismograph in terms of certain seismic parameters such as magnitude, epicenter and source properties. Initial results in terms of the proposed protocol are also presented showing an adequate performance of the propose low cost seismograph.

Keywords:
low-cost instruments, Ionian islands, performance protocol

Acknowledgements
«Telemachus – Innovative Seismic Risk Management Operational System of the Ionian Islands» which is part of the Operational Program «Ionian Islands 2014-2020» and is co-financed by the European Regional Development Fund (ERDF) (National Strategic Reference Framework - NSRF 2014-20).

How to cite: Avlonitis, M., Krokidis, S., Vlachos, I., Karakostas, V., and Kostoglou, A.: Building a perfomance protocol of a low cost seismograph, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18524, https://doi.org/10.5194/egusphere-egu2020-18524, 2020.

As the community further expands their scope of study, pushing into different sub-disciplines and evermore challenging environments, the need for dynamic and highly adaptable systems grows. One of the challenges for instrument pool managers is finding a system that can cater for a wide range of possible use scenarios.

This is where traditional broadband, force-feedback sensors meet their limitations: with constrained frequency responses and sensitivities, they tend to target very narrow applications offering limited flexibility. When managing a pool of instruments, this translates into increasing pressure to acquire multiple units within different instrument ranges to meet the requirements for each specific application. This in turn leads to complex pool maintenance and may require operators to use unfamiliar instruments if their first choice is being used owing to a reduced number of instruments for each application within the pool.

Güralp’s 35 years’ experience in working with major national instrument pools revealed the necessity to develop flexible, easy-to use systems that could fit a wider scope of applications. This has led to a new, highly versatile smart sensor that supports extensive user configuration and ultra-wide tilt ranges.

The new sensor has a configurable long period corner allowing for rapid deployment in a range of environments: the 1s mode ensures the sensor settles quickly for rapid response purposes, and the 120s mode is ideally suited for long period observation.

The group of products that use this technology deliver high sensor reliability, sophisticated tools for ease of instrument and data management as well as industry standard data formats. The sensors have been integrated into various instruments: the Certimus for surface and shallow burial, the Radian for deeper postholes and boreholes, and the Fortimus for strong-motion applications.  The same philosophy also brought about Aquarius, an Ocean Bottom Seismometer that utilises the same sensor technology for the benefit of OBS pools.

This family of just four instruments covers the vast majority of seismic monitoring requirements. They represent Güralp’s solution to make instrument pool management easier and more affordable.

How to cite: Mohr, S., Balon, M., Filippi, S., Watkiss, N., and Hill, P.: Simplifying Instrument Pools: The Next Generation Family of Smart Instrumentation., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19522, https://doi.org/10.5194/egusphere-egu2020-19522, 2020.

Exploitation of super-critical water from deep geothermal resources can potentially give a 5-10 fold increase in the power output per well. Such an improvement represents a significant reduction in investment costs for deep geothermal energy projects, thus improving their competiveness.

In the previous European Horizon2020 DESCRAMBLE (Drilling in dEep, Super-CRitical AMBients of continental Europe) project it was demonstrated drilling of a deep geothermal well with super-critical conditions (>375°C, >220 bar) by extending an existing well in Larderello, Italy to a depth of around 4km. As state-of-the-art electronic logging tools could not operate reliably at these conditions, DESCRAMBLE developed and tested a novel pressure and temperature logging tool for these supercritical conditions. Target specification for the slickline operated tool was 8 hours logging operation time at 450°C/450 bar, limited by the critical temperature for the available battery technology used for the application. During testing in the supercritical well in Larderello, Italy in 2017, the tool recorded a maximum well temperature of 443.6°C.

The instrument developed in the DESCRAMBLE project, although being state-of-the-art in its performance, was costly and advanced in addition to having a larger outer diameter than desired in for example slim-well applications. Therefore, there is a need for a simpler, lower cost version of this tool with a smaller outer diameter.

The tool being developed, based on the H2020 DESCRAMBLE project, consists of off-the-shelf high temperature electronics, sensors and batteries shielded from the environment by a heat and pressure shield (Dewar). The target specification for the tool is 600°C/500Bar, with a shorter operational time than the DESCRAMBLE tool.

In this work, we describe the tool requirements and discuss the design choices made regarding mechanical parts, seals, electronics platform, sensors, and available battery technology. 3D CAD drawings and simulations of the thermal performance of the tool will be presented, as well as preliminary test results of the electronic platform combined with the sensors and batteries. Production and testing of the physical tool will not be within the scope of the project.

How to cite: Hamremoen Røed, M.: Development of a Low Cost Novel PT Logging Tool for High Temperature Operation (600°C), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21488, https://doi.org/10.5194/egusphere-egu2020-21488, 2020.