Polarization Tomography with Stokes Parameters

We present a simple but powerful technique for the analysis of polarized emission from radio galaxies and other objects. It is based on the fact that images of Stokes parameters often contain considerably more information than is available in polarized intensity and angle maps. In general, however, the orientation of the Stokes parameters will not be matched to the position angles of structures in the source. Polarization tomography, the technique presented in this paper, consists of making a series of single linear Stokes parameter images, S(ρ), where each image is rotated by an angle ρ from the initial orientation of Q and U. Examination of these images, in a series of still frames or a movie, reveals often hidden patterns of polarization angles, as well as structures that were obscured by the presence of overlapping polarized emission. We provide both cartoon examples and a quick look at the complex polarized structure in Cygnus A.

The Pisciarelli main fumarole mechanisms reconstructed by electrical resistivity and induced polarization imaging

Pisciarelli, together with the adjacent Solfatara maar-diatreme, represents the most active structure of the Campi Flegrei caldera (Italy) in terms of degassing and seismic activity. This paper aims to define the structure of the Pisciarelli hydrothermal system (down to a 20 m depth) through electrical resistivity and time-domain-induced polarization tomography and self-potential mapping. The retrieved 3D image of the area helps reconstruct the Pisciarelli subsurface in its area of maximum degassing, containing the main fumarole (“soffione”) and the mud pool. In particular, a channel has been identified in which fluids stored in a deeper reservoir rise toward the surface. Such a structure seems to be surmounted by a clay-cap formation that could govern the circulation of fluids and the abundance of gases/vapors emitted by the soffione. Based on this new reconstruction of the Pisciarelli fumarolic field structural setting, the first conceptual model has been suggested that is capable of simultaneously explaining the mechanisms governing soffione activity and elucidating the role played by the fluid/gas of deeper origin in the shallow fluid circulation system. The proposed model can potentially help to better monitor the processes occurring throughout the Pisciarelli fumarolic field and provide an evaluation of the associated hazards.

Induced Polarization as a Tool to Assess Alteration in Geothermal Systems: A Review

The mineral alteration patterns in high- to low-temperature geothermal fields affect the induced polarization (electrical conductivity and chargeability) properties of volcanic rocks. Indeed, these properties are sensitive to the cation exchange capacity and the porosity of the rock, which are both dependent on the alteration path, temperature, and depth of burial. Therefore induced polarization tomography appears as a powerful non-intrusive geophysical method to investigate alteration patterns in geothermal fields. Among clay minerals, the production of smectite through prograde reactions occurs progressively in volcanic rocks up to 220 °C. The presence of smectite dominates the induced polarization response of the volcanic rocks because of its very large cation exchange capacity. It follows that induced polarization can be used as a non-intrusive temperature proxy up to 220 °C for both active and inactive geothermal fields, recording the highest temperatures reached in the past. The influence of magnetite and pyrite, two semi-conductors, also has a strong influence regarding the induced polarization properties of volcanic rocks. Various field examples are discussed to show how induced polarization can be used to image volcanic conduits and smectite-rich clay caps in volcanic areas for both stratovolcanoes and shield volcanoes.

Temperature distribution in a permafrost-affected rock ridge from conductivity and induced polarization tomography

Summary Knowledge of the thermal state of steep alpine rock faces is crucial to assess potential geohazards associated with the degradation of permafrost. Temperature measurements at the rock surface or in boreholes are however expensive, invasive, and provide spatially-limited information. Electrical conductivity and induced polarization tomography can detect permafrost. We test here a recently developed petrophysical model based on the use of an exponential freezing curve applied to both electrical conductivity and normalized chargeability to infer the distribution of temperature below the freezing temperature. We then apply this approach to obtain the temperature distribution from electrical conductivity and normalized chargeability field data obtained across a profile extending from the SE to NW faces of the lower Cosmiques ridge (Mont Blanc massif, Western European Alps, 3613 m a.s.l., France). The geophysical datasets were acquired both in 2016 and 2019. The results indicate that the only NW face of the rock ridge is frozen. To evaluate our results, we model the bedrock temperature across this rock ridge using CryoGRID2, a 1D MATLAB diffusive transient thermal model and surface temperature time series. The modelled temperature profile confirms the presence of permafrost in a way that is consistent with that obtained from the geophysical data. Our study offers a promising low-cost approach to monitor temperature distribution in Alpine rock walls and ridges in response to climate change.

POLARIZATION TOMOGRAPHY METHODS TO DIFFERENTIATE ASEPTIC AND SEPTIC LOOSENING AFTER TOTAL HIP REPLACEMENT

This article contains: • Structural-logical scheme and analytical description of the differential diagnosis for aseptic and septic loosening after total hip replacement using the methods of differential Mueller-matrix mapping of circular birefringence (CB) distributions of polycrystalline synovial fluid (SF) films. • Statistical analysis of the distributions of CB in polycrystalline SF films obtained from patients in the control group and groups with different hip joint pathology. • Results of establishing the strength of the differential Mueller-matrix mapping method of the distributions of CB polycrystalline films of SF by means of information analysis based on sensitivity determination, specificity and accuracy of the polarization tomography technique. • Clinical example of using polarization tomography methods to differentiate aseptic and septic cup loosening after total hip replacement

DIAGNOSTIC POSSIBILITIES OF ANALYSIS OF THE MAP OF LINEAR BIREFRINGENCE OF THE CRYSTAL FRACTION OF VITREOUS BODY FOR ACCURATE DETERMINATION OF THE TIME SINCE DEATH

Introduction: This paper discusses the possibility of polarization microscopic tomography of polycrystalline structure of vitreous body (VB) for use in forensics and in determining the time since death (TSD). Objectives: The purpose of this study was to develop a new set of forensic criteria to enhance the functionality of the high-precision definition of TSD over a long period of time according to polarization microscopic tomography of the polycrystalline structure of the VB of the human eye by statistical and wavelet analysis. Results: We obtained the numerical values of the change in the magnitude of the statistical moments of the 1-4 orders, which characterize the coordinate distributions of the magnitude of the linear birefringence (LB) of the polycrystalline component of the VB by the magnitude of the TSD. The results from our research illustrate the differences between the optical anisotropy of fibrillar collagen networks of VB layers with different TSD. The sensitivity range (36 hours) and accuracy (15 minutes) of the method of polarization tomography of the LB distributions of the polycrystalline component of the VB layers in the determined TSD were established. Conclusion: These results confirm the experimental processes outlined accurately determine the time of death. In turn, will provide scientific evidence, specifications thereof, and objective expert opinion.