Johan Robertsson

Last Name

Robertsson

First Name

Johan

ORCID

0000-0002-3292-385X

Organisational unit

03953 - Robertsson, Johan / Robertsson, Johan

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Publications 1 - 10 of 46

Acoustic Cloning
van Manen, Dirk-Jan; Becker, Theodor Simon; Li, Xun; et al. (2022)
The InSight HP³ Penetrator (Mole) on Mars: Soil Properties Derived from the Penetration Attempts and Related Activities
Spohn, Tilman; Hudson, Troy L.; Marteau, Eloïse; et al. (2022)
Space Science Reviews
The NASA InSight Lander on Mars includes the Heat Flow and Physical Properties Package HP3 to measure the surface heat flow of the planet. The package uses temperature sensors that would have been brought to the target depth of 3–5 m by a small penetrator, nicknamed the mole. The mole requiring friction on its hull to balance remaining recoil from its hammer mechanism did not penetrate to the targeted depth. Instead, by precessing about a point midway along its hull, it carved a 7 cm deep and 5–6 cm wide pit and reached a depth of initially 31 cm. The root cause of the failure – as was determined through an extensive, almost two years long campaign – was a lack of friction in an unexpectedly thick cohesive duricrust. During the campaign – described in detail in this paper – the mole penetrated further aided by friction applied using the scoop at the end of the robotic Instrument Deployment Arm and by direct support by the latter. The mole tip finally reached a depth of about 37 cm, bringing the mole back-end 1–2 cm below the surface. It reversed its downward motion twice during attempts to provide friction through pressure on the regolith instead of directly with the scoop to the mole hull. The penetration record of the mole was used to infer mechanical soil parameters such as the penetration resistance of the duricrust of 0.3–0.7 MPa and a penetration resistance of a deeper layer (> 30 cm depth) of 4.9±0.4 MPa. Using the mole’s thermal sensors, thermal conductivity and diffusivity were measured. Applying cone penetration theory, the resistance of the duricrust was used to estimate a cohesion of the latter of 2–15 kPa depending on the internal friction angle of the duricrust. Pushing the scoop with its blade into the surface and chopping off a piece of duricrust provided another estimate of the cohesion of 5.8 kPa. The hammerings of the mole were recorded by the seismometer SEIS and the signals were used to derive P-wave and S-wave velocities representative of the topmost tens of cm of the regolith. Together with the density provided by a thermal conductivity and diffusivity measurement using the mole’s thermal sensors, the elastic moduli were calculated from the seismic velocities. Using empirical correlations from terrestrial soil studies between the shear modulus and cohesion, the previous cohesion estimates were found to be consistent with the elastic moduli. The combined data were used to derive a model of the regolith that has an about 20 cm thick duricrust underneath a 1 cm thick unconsolidated layer of sand mixed with dust and above another 10 cm of unconsolidated sand. Underneath the latter, a layer more resistant to penetration and possibly containing debris from a small impact crater is inferred. The thermal conductivity increases from 14 mW/m K to 34 mW/m K through the 1 cm sand/dust layer, keeps the latter value in the duricrust and the sand layer underneath and then increases to 64 mW/m K in the sand/gravel layer below.
Fibre-Optic Monitoring of Seismic Events from an Alpine Slope Instability: Insights into Spatial and Temporal Dynamics
Kiers, Tjeerd; Grimm, Julius; Schmelzbach, Cédric; et al. (2025)
EGUsphere
Slope instabilities represent a significant hazard to communities and infrastructure across various regions worldwide. Climate change and resultant increasing severe precipitation events potentially raise the risk of failing mass movements. Therefore, a fundamental understanding of slope failure processes is vital for reducing risks. Established remote-sensing and synthetic aperture radar technologies provide valuable data on the surface movement of landslides, but only provide limited information on the instability’s internal state. In contrast, seismic imaging and monitoring techniques can provide critical complementary information on the subsurface structure, physical properties, and time-dependent processes linked to the slope instability dynamics. The ‘Cuolm da Vi’ slope instability near Sedrun (central Switzerland) represents one of the Alps’ largest active landslides, with an estimated volume of around 150 million m3 and maximum displacement rates of up to 20 cm per year. While the instability currently does not pose an imminent danger, the slope's surface displacement is under constant observation. However, little is known about the Cuolm da Vi internal structure and dynamics at depth. The primary objective of our project is to advance our understanding of the subsurface structures and processes over time, with potential implications for deepening our fundamental knowledge of toppling instabilities in general. In the summer of 2022, we established an extensive seismic observation network at Cuolm da Vi. This seismic sensor setup included over 1’000 autonomous seismic nodes and a 6-kilometer-long trenched fibre-optic cable. The fibre-optic sensing system was designed for long-term Distributed Acoustic Sensing (DAS) and Distributed Strain Sensing (DSS) observations. This multi-sensor geophysical network provides a unique spatial and temporal resolution for studying the Cuolm da Vi instability, allowing us to observe time-dependent changes across a wide range of spatial and temporal scales. Between summer 2022 and 2024, we gathered a comprehensive data set, including long-term continuous recordings from the nodal, DAS, and DSS systems. Using a DAS dataset continuously collected from February to July 2023, we developed a wavefield coherence-based workflow to detect and cluster over 7’000 events recorded along the fibre-optic cable. These event clusters of highly similar seismic signals were manually classified into categories such as regional earthquakes, anthropogenic noise, rockfalls, and local seismic events, based on their time- and frequency domain characteristics. The spatial and temporal distribution of several local seismic event clusters exhibits distinct patterns that correlate closely, for example, with the surface displacement measurements. We are currently analysing these clusters of local events and investigating whether spatial links to known tectonic structures can be established, and whether the observed seismic signals allow refining the hazard scenarios and associated early warning strategies.
On the benefit of collecting the seismic divergence using Distributed Acoustic Sensing with coiled fiber
Edme, Pascal; Kiers, Tjeerd; Sollberger, David Andres; et al. (2024)
EGUsphere
Distributed Acoustic Sensing (DAS) captures the longitudinal strain fluctuations along fiber optic cables. With locally straight cables, the measurement is closely related to the horizontal gradient of the horizontal velocity fields ∂xVx which could alternatively be obtained by differencing closely spaced conventional point sensors such as geophones and seismometers. The latter approach however often suffers from instrument and deployment perturbations as well as finite-difference bias and we discuss the advantage of using DAS to obtain higher fidelity gradients over a larger operating bandwidth, both spatially and temporally. We then introduce the potential of DAS to extract the divergence (∂xVx+∂yVy) of the seismic wavefield by interrogating horizontally coiled fiber. This results in an omni-directional measurement that is closely related to near-surface pressure fluctuations which, we demonstrate, is insensitive to Love waves but closely related the horizontal acceleration of particle motion H induced by Rayleigh waves. Such a wavefield separation is attractive for local ground-roll attenuation and reflection imaging with reduced field effort. We finally show that the H/D spectral ratio provides a local estimate of the Rayleigh wave dispersion curve(s). The proposed method does not rely on travel time analysis and applies to waves originating from any directions, therefore it is particularly suitable to process Rayleigh wave dominated ambient noise, as illustrated with a real data example collected in urban environment (Zurich, Switzerland). In brief, we propose a novel land acquisition and processing strategy that does not require dense sensor arrays nor active sources for cost-effective near-surface characterization.
Directional pre-sensitivity of the laser interferometer space antenna
Riegger, Franziska; Andersson, Fredrik; Robertsson, Johan (2024)
Physica Scripta
The space-based Laser Interferometry Space Antenna (LISA) is a gravitational waves observatory currently under development. It comprises three spacecraft, each traveling in a heliocentric orbit that is weakly eccentric and inclined. Gravitational waves comprise two polarization components. They will be detected by conducting interferometric Doppler measurements between the LISA spacecraft. Among other factors, the signal strength of the Doppler measurements will depend on the location of the GW source, the GW polarization angle, and the orbits of the spacecraft. Thus, the signal strength of the Doppler measurements will vary over time. For given spacecraft orbits, we derive bounds on the signal strength that are functions of the source location. These bounds are simple, explicit expressions, and we refer to them as the directional pre-sensitivity. Using the directional pre-sensitivity, we construct a metric for the relative change in the signal strength depending on the source location and the spacecraft orbits. We illustrate how this formalism can be used to assess the signal strength for several examples of chosen orbits.
Gradiometric sensors design for sub-Nyquist wavefield reconstruction
Piciucco, Davide; Serra-Garcia, Marc; Robertsson, Johan (2025)
On the use of multicomponent streamer recordings for reconstruction of pressure wavefields in the crossline direction
Robertsson, Johan; Moore, Ian; Vassallo, Massimiliano; et al. (2008)
Geophysics
Three-component measurements of particle motion would bring significant benefits to towed-marine seismic data if processed in conjunction with the pressure data. We show that particle velocity measurements can increase the effective Nyquist wavenumber by a factor of two or three, depending on how they are used. A true multicomponent streamer would enable accurate data reconstruction in the crossline direction with cable separations for which pressure-only data would be irrecoverably aliased. We also show that conventional workflows aimed at reducing these aliasing effects, such as moveout correction applied before interpolation, are compatible with multicomponent measurements. Some benefits of velocity measurements for deghosting data are well known. We outline how the new measurements might be used to address some long-standing deghosting challenges of particular interest. Specifically, we propose methods for recovering de-ghosted data between streamers and for 3D deghosting of seismic data at the streamer locations.
Distributed Fiber-Optic Sensing for Local Ground-Roll Estimation and Attenuation
Edme, Pascal; Kiers, Tjeerd; Paitz, Patrick; et al. (2022)
83rd EAGE Annual Conference & Exhibition 2022
Distributed acoustic sensing usually aims at collecting spatially unaliased inline strain over tens of kilometers with a single optical fiber cable and associated interrogator. Here we explore the possibility of using this cost-effective technology to capture noise models and subsequently attenuate ground-roll originating from any directions (therefore including scattered noise) without relying on the traditional requirement of dense spatial sampling of geophones. We discuss a fiber cable layout composed of horizontal rings around the vertical geophones to measure the pseudo-pressure fluctuations, or equivalently the omni-directional divergence of the wavefield. Synthetic and field data confirm that loop circumference fluctuations are mainly generated by the Rayleigh wave train, in contrast to reflection signal. In addition, the proposed sensing approach seems more robust than finite-differencing additional horizontal geophone recordings. This suggests that a single additional component (complementary divergence via the interrogation of multiple fiber-optic rings) will allow sparser acquisition with reduced field effort and associated costs. Copyright © 2022 by the European Association of Geoscientists & Engineers (EAGE). All rights reserved
High-resolution 3D seismic characterization of an Alpine slope instability using a 1'000 node array
Kiers, Tjeerd; Schmelzbach, Cédric; Maurer, Hansruedi; et al. (2024)
EGUsphere
Slope instabilities, further destabilized by global warming and extreme weather conditions, pose increasing risks to life and property. Hence, understanding these potentially destructive phenomena is crucial to mitigate associated losses. Established approaches like remote sensing and radar-based observations yield important information on surface displacement. However, seismic imaging and monitoring techniques offer complementary insights into subsurface structures, physical properties and internal time-dependent processes that drive the slope instability evolution. The ‘Cuolm da Vi’ slope near Sedrun in Central Switzerland is one of the largest mass movements in the Alps (100-200 million m3) and is moving by up to 20cm/year. Even though it currently does not pose an immediate threat, the surface displacement of the slope instability is closely monitored. Yet, knowledge about its internal structure is limited such as, for example, the vertical extent of the unstable section which is suspected to reach several hundred meters in depth. The main objective of our project is to gain new insights into the slope instability structure and evolution. Furthermore, we aim to extend this towards innovative seismic strategies for the characterization and monitoring of large-scale mass movements in general. In summer 2022, we deployed an extensive seismic sensor network at Cuolm da Vi covering an area of approximately 0.6 km2. This network consisted of over 1'000 autonomous nodes arranged in a hexagonal grid pattern. In addition, we installed a 6-kilometer-long fiber-optic cable, targeted for long-term Distributed Acoustic Sensing (DAS) and Distributed Strain Sensing (DSS) measurements. This unique multi-sensor geophysical network enables us to investigate the unstable slope with an unprecedented level of spatial and temporal resolution, allowing us to monitor time-dependent changes over a broad spectrum of scales in space and time. During 2022 and 2023, we collected an extensive data set, including extended periods of continuous acquisition using the nodal, DAS, and DSS systems. During the summer 2022 acquisition period, we conducted a controlled-source seismic experiment to characterize the 3D subsurface structure using seismic imaging techniques. Recordings of 163 dynamite shots by the 1’000 node array resulted in more than 30’000 P-wave first-arrival travel-time picks. Using 3D travel-time tomography, we established a first 3D subsurface P-wave velocity model of the Cuolm da Vi body. The resultant tomograms exhibit strong lateral and vertical velocity contrasts, which correlate at the surface with mapped tectonic features and identified instable sections. Furthermore, velocity anomalies within the slope instability volume indicate significant structural and/or geological variations in space. In combination with the other seismic and geotechnical information, the 3D seismic velocity model allows us to, for example, revise hazard scenarios.
Can You Hear the Shape of a Virtual Acoustic Space?
van Manen, Dirk-Jan; Robertsson, Johan (2023)
VDT-Magazin: die Fachzeitschrift für Tonmeister
In 1966, Polish American mathematician Mark Kac (1966) wrote an article with the now famous title: “Can One Hear the Shape of a Drum?”. The frequencies at which a drumhead vibrates depend on its shape. In the article, Kac asked the question whether the shape can be uniquely determined if the frequencies are known. It took until the early 1990s for three mathematicians Gordon, Webb, and Wolpert to show that there indeed exist multiple shapes, that vibrate with exactly the same frequencies.

Publications 1 - 10 of 46

Johan Robertsson

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