A Closed-Form Expression of the Electromagnetic Tensor Green's Functions for a Homogeneous TI-Anisotropic Medium

In this letter, the electromagnetic fields from electric and magnetic current source distributions located in an unbounded homogeneous transverse isotropic (TI)-anisotropic medium are determined. The expressions provide the closed-form tensor Green's functions needed in any integral equation formulation of the forward as well as the inverse scattering problems associated with scatterers embedded in a homogeneous TI-anisotropic medium     

Non-linear three-dimensional inversion of cross-well electrical measurements

Cross-well electrical measurement as known in the oil industry is a method for determining the electrical conductivity distribution between boreholes from the electrostatic field measurements in the boreholes. We discuss the reconstruction of the conductivity distribution of a three-dimensional domain. The measured secondary electric potential field is represented in terms of an integral equation for the vector electric field. This integral equation is taken as the starting point to develop a non-linear inversion method, the so-called contrast source inversion (CSI) method. The CSI method considers the inverse scattering problem as an inverse source problem in which the unknown contrast source (the product of the total electric field and the conductivity contrast) in the object domain is reconstructed by minimizing the object and data error using a conjugate-gradient step, after which the conductivity contrast is updated by minimizing only the error in the object. This method has been tested on a number of numerical examples using the synthetic 'measured' data with and without noise. Numerical tests indicate that the inversion method yields a reasonably good reconstruction result, and is fairly insensitive to added random noise.     

Identification of hydrothermal alteration minerals associated with geothermal system using ASTER and Hyperion satellite data: a case study from Yankari Park,NE Nigeria

Concealed and fossilized geothermal systems are not characterized by obvious surface manifestations like hotsprings and fumaroles, therefore, could not be easily identifiable using conventional techniques. In this investigation, the applicability of Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) and Hyperion data-sets were evaluated in discriminating hydrothermal alteration minerals associated with geothermal systems as a proxy in identifying subtle Geothermal systems at Yankari Park, Nigeria. Feature-oriented principal component selection, spectral angle mapper, linear spectral unmixing were applied to ASTER data based on spectral characteristics of hydrothermal alteration key minerals for a systematic selective extraction of the information of interest. Analytical imaging and geophysics-developed processing methods were applied to Hyperion data for mapping iron oxide/hydroxide minerals and clay mineral assemblages in hydrothermal alteration zones. The results indicate that ASTER and Hyperion could be complemented for reconnaissance stage of targeting subtle alteration mineral assemblages associated with geothermal systems.     

People and sustainable land management: assessment of stakeholders knowledge of the nature of landuse/cover change in Abuja,Nigeria

Nature of Landuse/Land cover (LULC) changes has been assessed for many ecosystems, but there is limited knowledge on how different stakeholders perceive such changes. Information on this is required before sound interventions to address adverse impacts of the changes can be introduced. This paper utilised secondary and questionnaire survey data, complimented with focus group discussion, to assess how different stakeholders (famers, forestry workers, construction workers, artisans, resource managers, civil servants and private sector workers) perceive LULC changes induced by urban growth in rural (Karshi and Orozo) and urban (Karu and Nyanya) areas of Abuja Municipal Area Council (AMAC) of Federal Capital Territory, Nigeria. LULC change data revealed declines in cultivated areas, grasslands and bare lands, and corresponding expansion of built-up and vegetated areas over 1987–2014. Different stakeholders in both rural and urban locations of the area are generally aware of the nature of the changes. Those in rural locations have some very close interactions with features such as soil, water, and vegetation and are aware of the kinds of their changes. The urban dwellers are largely aware of changes in human aspects of the LULC. The respondents generally indicated that vegetation cover has been declining due to urban growth in the study area but secondary data analysis revealed opposite trend. Appropriate recommendations were given to improve soil, water and vegetation management in the study area.