Magnetic fields around radio galaxies from Faraday rotation measure analysis

The purpose of this thesis is to investigate the strength and structure of the magnetized medium surrounding radio galaxies via observations of the Faraday effect. This study is based on an analysis of the polarization properties of radio galaxies selected to have a range of morphologies (elongated tails, or lobes with small axial ratios) and to be located in a variety of environments (from rich cluster core to small group). The targets include famous objects like M84 and M87. A key aspect of this work is the combination of accurate radio imaging with high-quality X-ray data for the gas surrounding the sources. Although the focus of this thesis is primarily observational, I developed analytical models and performed two- and three-dimensional numerical simulations of magnetic fields. The steps of the thesis are: (a) to analyze new and archival observations of Faraday rotation measure (RM) across radio galaxies and (b) to interpret these and existing RM images using sophisticated two and three-dimensional Monte Carlo simulations. The approach has been to select a few bright, very extended and highly polarized radio galaxies. This is essential to have high signal-to-noise in polarization over large enough areas to allow computation of spatial statistics such as the structure function (and hence the power spectrum) of rotation measure, which requires a large number of independent measurements. New and archival Very Large Array observations of the target sources have been analyzed in combination with high-quality X-ray data from the Chandra, XMM-Newton and ROSAT satellites. The work has been carried out by making use of: 1) Analytical predictions of the RM structure functions to quantify the RM statistics and to constrain the power spectra of the RM and magnetic field. 2) Two-dimensional Monte Carlo simulations to address the effect of an incomplete sampling of RM distribution and so to determine errors for the power spectra. 3) Methods to combine measurements of RM and depolarization in order to constrain the magnetic-field power spectrum on small scales. 4) Three-dimensional models of the group/cluster environments, including different magnetic field power spectra and gas density distributions. This thesis has shown that the magnetized medium surrounding radio galaxies appears more complicated than was apparent from earlier work. Three distinct types of magnetic-field structure are identified: an isotropic component with large-scale fluctuations, plausibly associated with the intergalactic medium not affected by the presence of a radio source; a well-ordered field draped around the front ends of the radio lobes and a field with small-scale fluctuations in rims of compressed gas surrounding the inner lobes, perhaps associated with a mixing layer.

A prediction model for personal radio frequency electromagnetic field exposure

Radio frequency electromagnetic fields (RF-EMF) in our daily life are caused by numerous sources such as fixed site transmitters (e.g. mobile phone base stations) or indoor devices (e.g. cordless phones). The objective of this study was to develop a prediction model which can be used to predict mean RF-EMF exposure from different sources for a large study population in epidemiological research. We collected personal RF-EMF exposure measurements of 166 volunteers from Basel, Switzerland, by means of portable exposure meters, which were carried during one week. For a validation study we repeated exposure measurements of 31 study participants 21 weeks after the measurements of the first week on average. These second measurements were not used for the model development. We used two data sources as exposure predictors: 1) a questionnaire on potentially exposure relevant characteristics and behaviors and 2) modeled RF-EMF from fixed site transmitters (mobile phone base stations, broadcast transmitters) at the participants' place of residence using a geospatial propagation model. Relevant exposure predictors, which were identified by means of multiple regression analysis, were the modeled RF-EMF at the participants' home from the propagation model, housing characteristics, ownership of communication devices (wireless LAN, mobile and cordless phones) and behavioral aspects such as amount of time spent in public transports. The proportion of variance explained (R2) by the final model was 0.52. The analysis of the agreement between calculated and measured RF-EMF showed a sensitivity of 0.56 and a specificity of 0.95 (cut-off: 90th percentile). In the validation study, the sensitivity and specificity of the model were 0.67 and 0.96, respectively. We could demonstrate that it is feasible to model personal RF-EMF exposure. Most importantly, our validation study suggests that the model can be used to assess average exposure over several months.

Real-Time Passive Capturing of the GSM Radio

This paper addresses the problem of service development based on GSM handset signaling. The aim is to achieve this goal without the participation of the users, which requires the use of a passive GSM receiver on the uplink. Since no tool for GSM uplink capturing was available, we developed a new method that can synchronize to multiple mobile devices by simply overhearing traffic between them and the network. Our work includes the implementation of modules for signal recovery, message reconstruction and parsing. The method has been validated against a benchmark solution on GSM downlink and independently evaluated on uplink channels. Initial evaluations show up to 99% success rate in message decoding, which is a very promising result. Moreover, we conducted measurements that reveal insights on the impact of signal power on the capturing performance and investigate possible reactive measures.

Sediment volume variations inferred from DGPS measurements within Bossons glacier proglacial area (Mont-Blanc massif, France)

This dataset presents Differential Global Positioning System data (DGPS) acquired within the Bossons glacier proglacial area. Bossons glacier is a rapidly retreating glacier and its proglacial area is deglaciated for ~30 years. Bossons stream is one of the outlets of the subglacial drainage system. It starts as a 800 m steep cascade reach, then flows through an area with gentler slope : the Plan des Eaux (PdE). PdE is a 300 m long, 50 m wide proglacial alluvial plain with an increasing channel mobility in the downstream direction but decreasing slope gradient and incision. As it may act a sediment trap, studying periglacial and proglacial erosion processes in the Bossons catchment requires to quantify PdE sediment volume evolution. A several meter-sized block located within Bossons proglacial area was set up as GPS base : its location was measured by one antenna (Topcon Hyper Pro) by performing 600 consecutive measurements throughout one day. A second antenna (Topcon Hyper Pro) was then used to measure XYZ location of points in the proglacial area with a ~2 m grid. Radio communication between the two antennas allowed differential calculations to be automatically carried out on field using the Topcon FC-250 hand controller. This methodology yields 3 cm XY and 1.5 cm Z uncertainties. DGPS data have been acquired through 10 campaigns from 2004 to 2014; campaigns from 2004 to 2008 cover a smaller area than those from 2010 to 2014. Digital Elevation Model (DEM) have been interpolated from DGPS data and difference between two DEMs yields deposited and eroded volume within PdE. Maps of PdE volume variation between two campaigns show that incision mainly occurs in the upper and lower sections where as deposition dominates in the middle section. Deposition, denudation and net rate (deposition rate - denudation rate) are calculated by normalizing volumes by DEM areas. Deposition dominates results with a mean net rate of 29 mm/yr. However, strong inter-annual variability exists and some years are dominated by denudation : -36 mm/yr and -100 mm/yr for 2006 and 2011, respectively. Nonetheless, oldest campaigns (2004 to 2008) were carried out on the lower part part of the alluvial plain and ruling them out to keep only complete DEM (2010 to 2014) yields a mean net rate of ~15 mm/yr. This results is coherent with field observations of both strong deposition (e.g. flood deposits) and strong erosion (e.g. 30 cm incision) evidences. Bossons glacier proglacial area is thus dynamic with year-to-year geormorphological changes but may leans toward increasing its mean elevation through a deposition dominated system.

Static GPS measurements and elevation model in the hinterland of Neumayer

As part of the CryoSat Cal/Val activities and the pre-site survey for an ice core drilling contributing to the International Partnerships in Ice Core Sciences (IPICS), ground based kinematic GPS measurements were conducted in early 2007 in the vicinity of the German overwintering station Neumayer (8.25° W and 70.65° S). The investigated area comprises the regions of the ice tongues Halvfarryggen and Søråsen, which rise from the Ekströmisen to a maximum of about 760 m surface elevation, and have an areal extent of about 100 km x 50 km each. Available digital elevation models (DEMs) from radar altimetry and the Antarctic Digital Database show elevation differences of up to hundreds of meters in this region, which necessitated an accurate survey of the conditions on-site. An improved DEM of the Ekströmisen surroundings is derived by a combination of highly accurate ground based GPS measurements, satellite derived laser altimetry data (ICESat), airborne radar altimetry (ARA), and radio echo sounding (RES). The DEM presented here achieves a vertical accuracy of about 1.3 m and can be used for improved ice dynamic modeling and mass balance studies.