Investigating the effect of data quality on time domain electromagnetic discrimination
Using field data and numerical simulations we investigate the effect of data quality on time domain electromagnetic discrimination. Data quality decreases when measurements contain responses not accounted for by our mathematical modelling. This can include instrument noise, inaccurately reported position and orientation information, geologic contributions to the signal, and loss of validity of the forward modelling. Survey design is critical to data quality in order to have sufficient sampling of data anomalies, and also to ensure that each target is illuminated such that both the axial and transverse components of the polarization can be excited and measured. For dipole model based discrimination algorithms, success is contingent upon the accuracy with which the components of the polarization tensor can be estimated. Field data from different survey modes are analysed to identify noise sources and provide quantitative estimates of the noise in each survey. Inversion results show that increased noise levels lead to greater spread in recovered parameters. Monte Carlo simulations are performed in order to investigate the importance of other data quality factors. Analysis of inversion results from the simulations show that anomaly size, signal to noise ratio, positioning error, line spacing and station spacing all play a role in the spread of recovered parameters. Through the analysis of our simulation results we propose a figure of merit as a means of quantifying different data quality factors with a single number and relate this number to the accuracy with which parameters can be estimated.
Adaptive Focusing for Source Localization in EMI Sensing of Metallic Objects: A Preliminary Assessment
This paper considers a technique to deal with the problem of detecting and localizing objects in the data processing of electromagnetic induction (EMI) sensing. The technique is formulated using the concept of source power, which in our case is defined as the averaged sum of squared elements of a dipolar polarizabiltiy tensor over a measured time window for a transient electromagnetic (TEM) system. Under the valid dipole approximation to an EMI target, the source is point-like and therefore should occupy a small volume in space. This is the fundamental basis of the energy focusing technique for localizing a source. To achieve a focusing effect on a specified source, a focusing operator is constructed by minimizing the total output power subject to a unity response constraint for that assumed source. A closed-form expression is derived for source power as a function of a source location and can be used blindly without knowledge of the number of objects. The source power is related to data via a data covariance matrix, which in practice is computed with enough data samples. The experiments were conducted with the simulated and real data collected by a standard Geonics EM-63 system. The results, which we regard as a proof-of-concept, show that the focusing technique, under adequate signal-to-noise ratio (SNR), is able to accurately localize sources and is promising in EMI array processing.
The Russian language maintenance and language contacts
In our introductory article, we outline the main sociolinguistic features of Russian as a heritage language of post-Soviet immigrants in European settings and beyond. We offer a general overview of the evolution of Russian as a global language, with a particular focus on its geodemographics and economic and social value as a lingua franca . Based on this, we analyse the main principles defining the maintenance of Russian as a language of migration and as a heritage language in different countries, and emphasise the most important questions that still need to be addressed in this field of research. The main objective of this special issue is to combine the most recent research on the vitality of different languages of post-Soviet republics in new political milieu, with a particular focus on European and Asian countries, but there are other objectives as well. We propose to explore the factors that have either favoured or hindered the maintenance and transmission of languages of post-Soviet immigrants and repatriates, and how these sociolinguistic processes become evident in language vitality on both private and public levels. Our special issue primarily addresses the questions of family language policy, new language contacts and their management, and linguistic landscape in heritage speakers, diasporas and their new settings in Europe, Asia and the US.