Polarization Survey Research Articles

LOFAR Deep Fields: Probing the sub-mJy regime of polarized extragalactic sources in ELAIS-N1

Context. Deep polarization surveys at low radio frequencies are key to cosmic magnetism studies: Larger catalogs of polarized extra-galactic sources and increased precision on Faraday rotation measures (RMs) make it possible to probe the magneto-ionic medium along the lines of sight of the sources and to construct denser RM grids. In a first paper, we presented a search for polarized sources in deep observations of the 25-square-degree area of the European Large Area ISO Survey-North 1 (ELAIS-N1) field with the LOw Frequency ARray (LOFAR) at 114.9-177.4 MHz. Aims. In this paper, we investigate the properties of the polarized radio galaxies and use the catalog to produce an RM grid of the field. Methods. After identifying the host galaxies and collecting redshift information, we characterized the radio galaxies in terms of their radio morphologies, rest-frame radio luminosities, and linear sizes. We calculated residual rotation measures (RRMs) by removing the Galactic RM and studied the variation in the RRMs with redshift and degree of polarization. We produced an RRM grid of the field and compared the positions of the polarized sources with those of galaxy clusters and superclusters. Results. The radio galaxies show a variety of morphologies, including diffuse emission; Fanaroff Riley type II sources make up about half of the sample. Using available multiband catalogs, we found redshifts for the hosts of all polarized sources in the range of 0.06-1.9. Polarized emission is detected mainly from large radio galaxies. The RRM values have a median close to zero, and they appear to be independent of redshift and degree of polarization. The sources in the lines of sight of clusters of galaxies and of a supercluster are indistinguishable in their polarization and RRM properties from the population of sources that are not behind these structures.

Confusion of extragalactic sources in the far-infrared: A baseline assessment of the performance of PRIMAger in intensity and polarization

Aims. Because of their limited angular resolution, far-infrared telescopes are usually affected by the confusion phenomenon. Since several galaxies can be located in the same instrumental beam, only the brightest objects emerge from the fluctuations caused by fainter sources. The PRobe far-Infrared Mission for Astrophysics imager (PRIMAger) will observe the mid- and far-infrared (25–235 μm) sky both in intensity and polarization. We aim to provide predictions of the confusion level and its consequences for future surveys. Methods. We produced simulated PRIMAger maps affected only by the confusion noise using the simulated infrared extragalactic sky (SIDES) semi-empirical simulation. We then estimated the confusion limit in these maps and extracted the sources using a basic blind extractor. By comparing the input galaxy catalog and the extracted source catalog, we derived various performance metrics as completeness, purity, and the accuracy of various measurements (e.g., the flux density in intensity and polarization or the polarization angle). Results. In intensity maps, we predict that the confusion limit increases rapidly with increasing wavelength (from 21 μJy at 25 μm to 46 mJy at 235 μm). The confusion limit in polarization maps is more than two orders of magnitude lower (from 0.03 mJy at 96 μm to 0.25 mJy at 235 μm). Both in intensity and polarization maps, the measured (polarized) flux density is dominated by the brightest galaxy in the beam, but other objects also contribute in intensity maps at longer wavelengths (∼30% at 235 μm). We also show that galaxy clustering has a mild impact on confusion in intensity maps (up to 25%), while it is negligible in polarization maps. In intensity maps, a basic blind extraction will be sufficient to detect galaxies at the knee of the luminosity function up to z ∼ 3 and 1011 M⊙ main-sequence galaxies up to z ∼ 5. In polarization for the most conservative sensitivity forecast (payload requirements), ∼200 galaxies can be detected up to z = 1.5 in two 1500 h surveys covering 1 deg2 and 10 deg2. For a conservative sensitivity estimate, we expect ∼8000 detections up to z = 2.5, opening a totally new window on the high-z dust polarization. Finally, we show that intensity surveys at short wavelengths and polarization surveys at long wavelengths tend to reach confusion at similar depth. There is thus a strong synergy between them.

Nonparametric Bayesian reconstruction of Galactic magnetic fields using information field theory

Context. Ultrahigh-energy cosmic rays (UHECRs) are charged particles with energies surpassing 1018 eV. Their sources remain elusive because they are obscured by deflections caused by the Galactic magnetic field (GMF). This challenge is further complicated by our limited understanding of the 3D structure of the GMF because current GMF observations primarily consist of quantities that are integrated along the line of sight (LOS). Nevertheless, data from upcoming stellar polarization surveys along with Gaia stellar parallax data are expected to yield local GMF measurements. Aims. This study is the second entry in our exploration of a Bayesian inference approach to the local GMF that uses synthetic local GMF observations that emulate forthcoming local GMF measurements, and attempts to use them to reconstruct its 3D structure. The ultimate aim is to trace back observed UHECRs and thereby update our knowledge about their possible origin. Methods. In this proof-of-concept work, we assumed as ground truth a magnetic field produced by a dynamo simulation of the Galactic ISM. We employed methods of Bayesian statistical inference in order to sample the posterior distribution of the GMF within part of the Galaxy. By assuming a known rigidity and arrival direction of an UHECR, we traced its trajectory back through various GMF configurations drawn from the posterior distribution. Our objective was to rigorously evaluate the performance of our algorithm in scenarios that closely mirror the setting of expected future applications. In pursuit of this, we conditioned the posterior to synthetically integrated LOS measurements of the GMF, in addition to synthetic local plane of sky-component measurements. Results. Our results demonstrate that for all locations of the observed arrival direction on the plane of sky, our algorithm is able to substantially update our knowledge on the original arrival direction of UHECRs with a rigidity of E/Z = 5 × 1019 eV, even without any LOS information. When the integrated data are included in the inference, the regions of the celestial sphere in which the maximum error occurs are greatly reduced. The maximum error is diminished by a factor of about 3 even in these regions in the specific setting we studied. Additionally, we are able to identify the regions in which the largest error is expected to occur.

Antenna-Coupled Magnetic Microbolometers for CMB Polarization Surveys

In this work, we propose a magnetic bolometer to be employed in the search of primordial B-modes in the CMB. These magnetic bolometers are an adaptation of the well-known metallic magnetic calorimeters used in particle physics. They rely on the magnetization dependence on temperature of alloys such as Au:Er and Ag:Er. In addition to the low intrinsic noise a magnetic bolometer of this nature offers, the broad and smooth temperature-dependent magnetization of metallic magnetic sensors ultimately translates to a high dynamic range and straightforward calibration. Their intrinsic noise equivalent power (NEP) is estimated to be in the range of 10–100 aW/(Hz)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\sqrt{(}\ ext {Hz})$$\\end{document}. We outline here a workable design for such a detector utilizing an antenna-coupled approach and present the simulated power transfer ratio that was attained; the detector’s performance is discussed by combining this result with its responsivity.

Spread Spectrum Induced Polarization (SSIP) Survey for the Qiushuwan Copper–Molybdenum Deposits in Southern Henan Province, China

Spread Spectrum Induced Polarization (SSIP) Survey for the Qiushuwan Copper–Molybdenum Deposits in Southern Henan Province, China

Investigation of the radial profile of galactic magnetic fields using rotation measure of background quasars

Probing magnetic fields in high-redshift galactic systems is crucial to investigate galactic dynamics and evolution. Utilizing the rotation measure of the background quasars, we have developed a radial profile of the magnetic field in a typical high-z galaxy. We have compiled a catalog of 59 confirmed quasar sightlines, having one intervening Mg II absorber in the redshift range 0.372 ≤ z abs ≤ 0.8. The presence of the foreground galaxy is ensured by comparing the photometric and spectroscopic redshifts within 3σ z-photo and visual checks. These quasar line-of-sights (LoS) pass through various impact parameters (D) up to 160 kpc, covering the circumgalactic medium of a typical Milky-Way type galaxy. Utilizing the residual rotation measure (RRM) of these sightlines, we estimated the excess in RRM dispersion, σ ex RRM. We found σ ex RRM decreases with increasing D. We translated σ ex RRM to average LoS magnetic field strength, 〈 B ∥ 〉 by considering a typical electron column density. Consequently, the decreasing trend is sustained in the magnetic field. In particular for sightlines with D ≤ 50 kpc and D> 50 kpc, 〈 B ∥ 〉 is found to be 2.39 ± 0.7 μG and 1.67 ± 0.38 μG, respectively. This suggests a clear indication of varying magnetic field from the disk to the circumgalactic medium. This work provides a methodology that, when applied to ongoing and future radio polarisation surveys such as LOFAR and SKA, promises to significantly enhance our understanding of magnetic field mapping in galactic systems.

Application of Geophysical Methods in the Identification of Mineralized Structures and Ranking of Areas for Drilling as Exemplified by Alto Guaporé Orogenic Gold Province

Mineral exploration works conducted in the Alto Guaporé Gold Province (AGGP), situated in the southwest region of the Amazon Craton in Brazil, faces the challenges of many gold provinces around the world, i.e., declines in the discoveries of new economic deposits and increases in exploration costs. Ground geophysical methods, combined with structural analyses and geological mapping, are valuable tools that have potential to improve accuracy in selecting exploration targets and in determining drilling locations. AGGP deposits are primarily associated with regional N20°–W50° inverse faulting and sheared geologic contacts between Meso-Neoproterozoic siliciclastic metasedimentary rocks and Mesoproterozoic basement (granite and volcano–sedimentary sequences). Mining currently occurring in the central portion of the province drives exploration works towards the many existing targets at the area. Among them, the ABP target is one of the most promising for being located few kilometers north of the Pau-a-Pique mine. At the ABP target, gold is associated with hydrothermal alteration located in the sheared contacts and in the hinge zone of folded metasedimentary sequence. Hydrothermal phases include Fe-oxides, sulfide (py), muscovite and quartz veins. In this study, we use magnetic and geoelectric (induced polarization) surveys coupled with structural and geological mapping to identify potential footprints within the ABP target. The results from induced polarization (IP) profiles successfully mapped the shape and orientation of the main structures down to approximately 350 m at the ABP target, indicating potential locations for hydrothermal alteration hosting gold. Additionally, 3D magnetic data inversions illustrated the distribution of magnetic susceptibilities and magnetization vectors associated with shear zone structures and isolated magnetic bodies. Magnetic data highlighted fault zones along the contacts between metamorphic rocks and granites, while IP data identified areas with high chargeability, correlating with sulfidation zones mineralized with gold. These findings suggest a metallogenic model where gold deposits are transported through deep structures connected to regional faults, implying significant tectonic and structural control over gold deposition. The results underscore the potential of multiparameter geophysics in identifying and characterizing deposits in both deep and strike, thereby advancing our understanding of mineral occurrences in the region and enhancing the search for new mineralized zones.

Discovery and Exploration of the Luming Porphyry Mo Deposit, Northeastern China: Implications for Regional Prospecting

Over the past two decades, significant deposit discoveries were made in Northeastern China, including the super-large Chalukou, Daheishan, and Luming porphyry Mo deposits. The discovery of the Luming deposit was accomplished through verification of stream sediment anomalies, with mineralization closely associated with early Jurassic monzogranite and granite porphyry. Previous studies primarily focused on the mineralization mechanisms of these deposits without adequately addressing the exploration methods and prospecting criteria. This study involved a comprehensive re-evaluation of geological observations, analysis of rock primary halo, gravity and magnetic surveys, and induced polarization surveys conducted during exploration campaigns at the Luming porphyry Mo deposit. The results suggest that hydrothermal breccias play a critical role in controlling the mineralization by forming a central low-grade core within the deposit while the Mo mineralization and hydrothermal alteration exhibit a donut-shaped distribution around it. The primary halo shows a distinct metal zonation moving from a central W-Bi-Mo-(Sb) to a peripheral Cu-Co-Ni and a distal Pb-Zn-Ag-In. The mineralization zone exhibits a low Bouguer gravity anomaly, negative magnetic anomaly, medium to low resistivity, and moderate to high chargeability, indicating the effectiveness of geophysical methods in defining the extent of the ore body. The Luming porphyry Mo deposit and distal skarn-epithermal Pb-Zn mineralization are parts of a porphyry-related magmatic-hydrothermal system. The results of this study offer valuable insights into the genesis of porphyry Mo deposits and their implications for prospecting in the forested region of Northeastern China.

Integrated geochemical and geophysical monitoring for the assessment of natural pollutant mitigation in heavy metal-contaminated areas of South Korea, Deagu.

The evaluation and monitoring of sites contaminated with heavy metals are essential for pollution remediation and prevention. In this study, we conducted geophysical and geochemical investigations at a site exhibiting heavy metal contamination downstream from an abandoned mine, with the aim of analyzing the extent of contamination and its temporal variation. We employed geophysical survey methods including electrical resistivity and induced polarization surveys of areas contaminated with heavy metals. Repeated surveys were conducted over time using the electrical resistivity method. Numerical simulations were employed to mitigate and eliminate electrical noise stemming from topography on the site. Additionally, time-lapse inversion was conducted on the resistivity data sets to analyze the changes in resistivity caused by variations in heavy metal contaminants. In the geochemical survey, soil samples were collected from the same locations as the geophysical survey, and chemical properties including pH, water content, electrical conductivity, and cation exchange capacity were analyzed. Our results showed that with the reduction of major sources of As and Zn contamination by 50%, the time-lapse electrical resistivity inversion results indicated that the resistivity of the subsurface materials increased by a factor of two. This paper demonstrated the natural reduction of the heavy metal contaminants at the site due to rainfall, aiming to comprehensively analyze the resultant alteration of both geochemical and geophysical properties.

Interstellar Polarization Survey. IV. Characterizing the Magnetic Field Strength and Turbulent Dispersion Using Optical Starlight Polarization in the Diffuse Interstellar Medium

Angular dispersion functions are typically used to estimate the fluctuations in polarization angle around the mean magnetic field orientation in dense regions, such as molecular clouds. The technique provides accurate turbulent-to-regular magnetic field ratios, 〈Bt2〉1/2/Bpos , which are often underestimated by the classic Davis–Chandrasekhar–Fermi method. We assess the technique's suitability to characterize the turbulent and regular plane-of-sky magnetic field in low-density structures of the nearby interstellar medium (ISM), particularly when the turbulence outer scale, δ, is smaller than the smallest scale observed, ℓ min. We use optical polarization maps of three intermediate-latitude fields (∣b∣ ≳ 7.°5) with dimensions of 0.°3 × 0.°3, sourced from the Interstellar Polarization Survey–General ISM catalog. We decomposed the H i emission detected by the Galactic All-Sky Survey within our fields to estimate the multiphase ISM properties associated with the structure coupled to the magnetic field. We produced maps of the plane-of-sky magnetic field strength (B pos), mass density (ρ), and turbulent velocity dispersion (σ v,turb). In the regions with well-defined structures at d < 400 pc, the average B – ranges from ∼3 μG to ∼9 μ G, depending on the method and physical properties. In the region where structures extend up to 1000 pc, B pos varies from ∼1 to ∼3 μ G. The results agree with previous estimations in the local, diffuse ISM. Finally, optical starlight polarization and thermal dust polarization at 353 GHz consistently reveal a highly regular plane-of-sky magnetic field orientation unfazed by diffuse dust structures observed at 12 μm.

A MeerKAT Polarization Survey of Southern Calibration Sources

We report on full-Stokes L-band observations of 98 MeerKAT calibration sources. Linear polarization is detected in 71 objects above a fractional level of 0.2%. We identify ten sources with strong fractional linear polarization and low Faraday rotation measure that could be suitable for wide-band absolute polarization calibration. We detect significant circular polarization from 24% of the sample down to a detection level of 0.07%. Circularly polarized emission is seen only for flat spectrum sources α > −0.5. We compare our polarized intensities and Faraday synthesis results to data from the NVSS at 1400 MHz and the ATCA SPASS survey at 2300 MHz. NVSS data exist for 54 of our sources and SPASS data for 20 sources. The percent polarization and rotation measures from both surveys agree well with our results. The residual instrumental linear polarization for these observations is measured at 0.16%, and the residual instrumental circular polarization is measured at 0.05%. These levels may reflect either instabilities in the relative bandpass between the two polarization channels with either time or antenna orientation, or atmospheric/ionospheric variations with pointing direction. Tracking of the hourly gain solutions on J0408-6545 after transfer of the primary gain solutions suggests a deterioration of the gain stability by a factor of several starting about 2 hr after sunrise. This suggests that observing during the nighttime could dramatically improve the precision of polarization calibration.

Protoplanetary Disk Polarization at Multiple Wavelengths: Are Dust Populations Diverse?

Millimeter and submillimeter observations of continuum linear dust polarization provide insight into dust grain growth in protoplanetary disks, which are the progenitors of planetary systems. We present the results of the first survey of dust polarization in protoplanetary disks at 870 μm and 3 mm. We find that protoplanetary disks in the same molecular cloud at similar evolutionary stages can exhibit different correlations between observing wavelength and polarization morphology and fraction. We explore possible origins for these differences in polarization, including differences in dust populations and protostar properties. For RY Tau and MWC 480, which are consistent with scattering at both wavelengths, we present models of the scattering polarization from several dust grain size distributions. These models aim to reproduce two features of the observational results for these disks: (1) both disks have an observable degree of polarization at both wavelengths; and (2) the polarization fraction is higher at 3 mm than at 870 μm in the centers of the disks. For both disks, these features can be reproduced by a power-law distribution of spherical dust grains with a maximum radius of 200 μm and high optical depth. In MWC 480, we can also reproduce features (1) and (2) with a model containing large grains (a max = 490 μm) near the disk midplane and small grains (a max = 140 μm) above and below the midplane.

Prototype Faraday Rotation Measure Catalogs from the Polarisation Sky Survey of the Universe’s Magnetism (POSSUM) Pilot Observations

The Polarisation Sky Survey of the Universe’s Magnetism (POSSUM) will conduct a sensitive ∼1 GHz radio polarization survey covering 20,000 deg2 of the southern sky with the Australian Square Kilometre Array Pathfinder. In anticipation of the full survey, we analyze pilot observations of low-band (800–1087 MHz), mid-band (1316–1439 MHz), and combined-band observations for an extragalactic field and a Galactic plane field (low-band only). Using the POSSUM processing pipeline, we produce prototype rotation measure (RM) catalogs that are filtered to construct prototype RM grids. We assess typical RM grid densities and RM uncertainties and their dependence on frequency, bandwidth, and Galactic latitude. We present a median filter method for separating foreground diffuse emission from background components and find that after application of the filter, 99.5% of the measured RMs of simulated sources are within 3σ of their true RM, with a typical loss of polarized intensity of 5% ± 5%. We find RM grid densities of 35.1, 30.6, 37.2, and 13.5 RMs per square degree and median uncertainties on RM measurements of 1.55, 12.82, 1.06, and 1.89 rad m−2 for the median-filtered low-band, mid-band, combined-band, and Galactic observations, respectively. We estimate that the full POSSUM survey will produce an RM catalog of ∼775,000 RMs with median-filtered low-band observations and ∼877,000 RMs with median-filtered combined-band observations. We construct a structure function from the Galactic RM catalog, which shows a break at 0.°7, corresponding to a physical scale of 12–24 pc for the nearest spiral arm.

Magnetic Fields in the Southern Coalsack and Beyond

Starlight polarimetry, when combined with accurate distance measurements, allows for exploration of the three-dimensional structure of local magnetic fields in great detail. We present optical polarimetric observations of stars in and close to the Southern Coalsack, taken from the Interstellar Polarization Survey. Located in five fields of view approximately 0.°3 × 0.°3 in size, these data represent the highest density of optical polarimetric observations in the Southern Coalsack to date. Using these data, combined with accurate distances and extinctions based on Gaia data, we are able to characterize the magnetic field of the Coalsack and disentangle contributions to the polarization caused by the Southern Coalsack and a background structure. For the Southern Coalsack, we find an average magnetic field orientation of θ ∼ 75° with respect to the Galactic north pole and an average plane-of-sky magnetic field strength of approximately B POS = 10 μG, using the Davis–Chandrasekhar–Fermi method. These values are in agreement with some earlier estimates of the Coalsack’s magnetic field. In order to study the distant structure, we introduce a simple method to separate and isolate the polarization of distant stars from foreground contribution. For the distant structure, which we estimate to be located at a distance of approximately 1.3–1.5 kpc, we find an average magnetic field orientation of θ ∼ 100° and estimate a field strength of B POS ∼ 10 μG, although this will remain highly uncertain until the precise nature of the distant structure can be uncovered.

Assessment of Groundwater Potential as Alternative Water Resource for Kapar Power Plants

The current surface water shortage due to drought is prompting industries in Peninsular Malaysia to explore alternative water resources (AWR). Tenaga Nasional Berhad (TNB)’s reliance on town water has increased the risk of interruptions in supply, exposing the plant to shutdowns and reduced generation capacity. Consequently, TNB requires alternative water sources to mitigate these risks. This study aims to assess the groundwater potential at the Kapar Power Plant in terms of volume and quality as an alternative resource. Hydrogeological and geophysical surveys were conducted to locate prospective groundwater and determine its characteristics. Specifically, 2-D Electrical Resistivity Imaging (ERI) and Induced Polarization (IP) surveys were carried out using the ABEM Terrameter SAS 4000 and the ES10-64 electrode selector. A total of five survey lines were established, revealing four potential groundwater locations. However, two locations were selected for further evaluation, with a total yield of 15.5 m³/hr. This study provides valuable insights into utilizing groundwater as a sustainable alternative water source for TNB, helping to ensure operational stability and reliability for the power plant.

Delineation of LNAPL plumes in a clay-rich site in Gyeongsangnam-do Province, South Korea: integration of geophysical survey data with borehole data and soil sampling information.

To effectively delineate the spatial distribution of oil contaminant plumes, geophysical methods indirectly measure the physical properties of the subsurface and can provide spatial information and images on a large scale, as opposed to traditional direct methods such as borehole drilling, sampling, and chemical analysis, which are time-consuming and costly. However, interpreting geophysical responses over non-aqueous phase liquid (NAPL)-contaminated sites is not straightforward due to inconsistent responses from biodegraded oil contaminants. In this study, we performed multi-geophysical surveys including seismic refraction, ground-penetrating radar, electrical resistivity tomography (ERT), and induced polarization (IP) surveys, to locate NAPL-contaminated zones in a clay-rich site. To reduce ambiguity in discriminating between oil contaminants and clay layers, we first figure out the geological structure of the site by interpreting geophysical data incorporating with borehole data. The ERT data highlighted the heavily contaminated regions in the unsaturated zone but were less distinctive below groundwater levels. Conversely, IP responses revealed potential hotspots within the clay layers, extending beneath the groundwater. Considering the 3D geological model, NAPL-contaminated zones are properly delineated through interpretation of ERT and IP data together with borehole data, and the contaminant source zone was properly estimated within the site.

Robust and efficient CMB lensing power spectrum from polarization surveys

Robust and efficient CMB lensing power spectrum from polarization surveys

Sampling the Faraday rotation sky of TNG50: imprint of the magnetized circumgalactic medium around Milky Way-like galaxies

ABSTRACT Faraday rotation measure (RM) is arguably the most practical observational tracer of magnetic fields in the diffuse circumgalactic medium (CGM). We sample synthetic Faraday rotation skies of Milky Way-like galaxies in TNG50 of the IllustrisTNG project by placing an observer inside the galaxies at a solar circle-like position. Our synthetic RM grids emulate specifications of current and upcoming surveys; the NRAO VLA Sky Survey (NVSS), the Polarisation Sky Survey of the Universe’s Magnetism (POSSUM), and a future Square Kilometre Array (SKA1-mid) polarization survey. It has been suggested that magnetic fields regulate the survival of high-velocity clouds. However, there is only a small number of observational detections of magnetized clouds thus far. In the first part of the paper, we test conditions for the detection of magnetized circumgalactic clouds. Based on the synthetic RM samplings of clouds in the simulations, we predict upcoming polarimetric surveys will open opportunities for the detection of even low-mass and distant clouds. In the second part of the paper, we investigate the imprint of the CGM in the all-sky RM distribution. We test whether the RM variation produced by the CGM is correlated with global galaxy properties, such as distance to a satellite, specific star formation rate, neutral hydrogen covering fraction, and accretion rate to the supermassive black hole. We argue that the observed fluctuation in the RM measurements on scales less than 1○, which has been considered an indication of intergalactic magnetic fields, might in fact incorporate a significant contribution of the Milky Way CGM.

Diagnosis of 3D magnetic field and mode composition in MHD turbulence with Y-parameter

ABSTRACT Magnetic fields are crucial in numerous astrophysical processes within the interstellar medium (ISM). However, the detailed determination of magnetic field geometry is notoriously challenging. Based on the modern magnetohydrodynamic (MHD) turbulence theory, we introduce a novel statistical technique, the ‘Y-parameter’, to decipher the magnetic field inclination in the ISM and identify dominant turbulence modes. The Y-parameter, calculated as the ratio of anisotropies of different Stokes parameter combinations, displays contrasting trends with the mean-field inclination angle in Alfvénic and compressible turbulence modes. A Y-parameter value around 1.5 ± 0.5 provide a statistical boundary to determine the dominant MHD turbulence modes. We have discovered specific correlations between the Y-parameter value and the inclination angle that unveil the dominant turbulence mode. This methodology, when applied to future radio polarization surveys such as LOFAR and SKA, promises to significantly enhance our knowledge of 3D magnetic field in the ISM and improve our understanding of interstellar turbulence.

3D electrode configurations for spectral induced polarization surveys of landfills

There is growing interest in the use of spectral induced polarization (SIP) surveys to characterize the near-surface environment. Few attempts have been made to perform field SIP surveys in a 3D configuration; when done, they are typically conducted using a series of parallel 2D electrode lines with collinear measurements. However, such measurements are limited in the resolution between the lines which is critical in the case of heterogeneous subsurface conditions, such as in landfills. To overcome this, we investigate here the enhanced resolution in SIP measurements through true 3D measurements, i.e., the resolving capabilities of different electrode configurations distributed across measuring planes. First, we investigate, through a synthetic study, the difference between results from using 2D parallel collinear electrode arrays and true 3D configurations. Second, we collected SIP data (in the frequency range between 1 and 240 Hz) using 2D and 3D configurations in two landfills to evaluate the application of our results in real field conditions. Both the synthetic and the field experiments demonstrate that measurements of parallel 2D collinear arrays result in the creation of artifacts and the loss of resolution in the 3D structure, especially of polarizable features. In contrast, the 3D configurations are able to resolve polarizable anomalies in synthetic and field measurements, resulting in a better delineation of the geometry of waste units. Our results also demonstrate that 3D configurations are better suited to recover the frequency-dependence of the electrical properties; thus, permitting an improved interpretation of waste composition and the quantification of waste volume.