IEEE Std 356:2020 pdf free download – IEEE Guide for Measurements of Electromagnetic Properties of Earth Media
1.4 Background
The electromagnetic propertics of earth [conductivity a in siemens/meter (S/m),，permittivity s infarads/meter (F/m), and magnetic permeability u in henrics/meter(H/m)]can have a major effect upon theperformance of electrical and electromagnetic systems. Examples of these systems include bothcommunications systems and remote-sensing systems. For example,the electrical properties of the earthbeneath an antenna can influence the antenna efficiency (and the need for a metallic ground plane) andradiation pattern, and these properties also can limit the effective depth of ground-penetrating radar.Manydifferent methods and techniques have evolved for the measurement of the clectrical properties of the earthat and near the surface at radio frequencies, and other methods using lower frequencies were developed formeasuring the conductivity deeper into the earth for geophysical prospecting and other applications.
This guide is intended to describe these methods (both the theory and field methodology) and providereferences for further reading for each method. The descriptions represent the recommended practice ofthese techniques. There is a further attempt to provide guidance on the limits of applicability of themethods (e.g., in frequency or in geographical context).
This guide has been prepared by the Antennas and Propagation Standards Committee of the IEEE Antennasand Propagation Society to replace the document, IEEE Std 356-1974,IEEE Guide for Radio Methods ofMeasuring Earth Conductivity [B8], which was also published by de Bettencourt et al. [B6].’ In 1974, Lytle[B15] also published a comprehensive review paper.
The International Telecommunication Union (ITU) has published world surface conductivity maps for anumber of frequency bands (ITU-R Recommendation P.832-2 [B9J), although these maps are no longerbeing updated. The curves of conductivity and relative permittivity in ITU-R Recommendation 527-3[B10] exhibit no dispersion in the band 3 MHZ to 30 MHz, whereas measured values show significantdispersion in this band for which surface soils typically can show characteristics from good conductors tolossy dielectrics (King and Smith [B12]). The real and imaginary parts of the complex relative permittivityform a Hilbert transform pair.As a result, the conductivity and relative permittivity are not independentvariables. Their mutual dependence is described by the Kramers-Kronig relations (King and Smith [B12).Therefore, the ITU values for the high-frequency (HF) band are inconsistent with the results of complexvariable theory and are in error.
lt is well known that the physical and electromagnetic properties of the earth are highly non-uniform.Consequently the use of parameters o and s to describe the carth should take into account the fact that theycan be a function of spatial dimensions or can represent a composite value, which is directly affected by thenon-uniformity of the sample. In rock mechanics, these differences are described by the terms “”rock massto represent the non-uniform composite structure, and”rock material”to represent the uniform material(Brady and Brown [B2]). This distinction can also be made by differentiating between those methods ofmeasurements that are made in situ and those that are made on rock samples in the laboratory. Thisdistinction is also directly related to the wavelength of the radiation in the material under consideration andthe size and separation of the contact electrodes used in the measurement.
This document does not cover electrical or electromagnetic geophysical methods reported by Keller andFrischknecht [Bl1] that rely on mapping anomalies in the earth’s structure,unlcss such information isdirectly related to determining the electrical properties of such materials. These geophysical techniquesinclude magnetic tilt methods，magnetic surveys，most types of ground probing radar (GPR) and manyairborne and satellitc remotc-sensing techniques.This guide does include the methods used to provide“ground truth” for these mapping methods.
The frequency of measurement,porosity of rock, water content, temperature, pressure, and the degree offracture of the sample can affect measurement. Porosity is defined as the percentage of pore space in a unitvolume of rock. Pores in a rock are often filled with fluids that give rise to finite resistance. Whilemeasuring the conductivity，there can be significant problems with probe contacts，both for in-situmeasurements (probe impedance, conductive layers, etc.) and sample measurements (surface preparation,air gaps, etc.). In addition, these materials can be highly inhomogeneous, anisotropic, layered, and fracturedso that the orientation of the electrodes should play a significant part in determining the results obtained(Keller and Frischknecht [B11]).Anisotropy of a rock sample is scale-dependent. Consequently, electrodeorientation as well as the separation of electrodes can influence the anisotropy measurement.