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Table 11 Detailed nomenclature for geothermal and soil-related variables

From: A machine learning approach for mapping the very shallow theoretical geothermal potential

SymbolUnitDescription
\(\alpha\)(\(\text {m}^{2}\,\text {s}^{-1}\))Thermal diffusivity
\(\gamma _{d}\)(g/\(\text {cm}^{3}\))Dry (bulk) density
\(\gamma _{s}\)(g/\(\text {cm}^{3}\))Particle density
\(\gamma _{w}\)(g/\(\text {cm}^{3}\))Water density
\(\lambda\)(\(\text {W K}^{-1}\,\text {m}^{-1}\))Thermal conductivity
\(\rho\)(\(\Omega\) m)Electrical resistivity
\(\omega\)(\(\text {s}^{-1}\))Angular frequency of one period in Fourier series
\(a_{n}\)(–)First Fourier coefficient for the nth harmonics
\(b_{n}\)(–)Second Fourier coefficient for the nth harmonics
\(c_{v}\)(\(\text {J m}^{-3}\,\text {K}^{-1}\))Volumetric heat capacity
D(m)Damping depth
e(–)Void ratio
F(%)Percentage sum of sand and gravel fractions in the soil
\(h_{i}\)(m)Width of soil strata i
\(I_{1},...,I_{10}\)(–)Possible fraction intervals for soil texture variables
\(M_{s}\)(g)Mass of solid soil in ground
\(M_{w}\)(g)Mass of water in ground
n(–)Harmonics index in Fourier series
\(n_{p}\)(–)Porosity
\(R_{n}\)(–)Amplitude of nth harmonic of Fourier series solution for T
Sd, St, Cl(%)Sand, silt, and clay fraction percentage in soil
\(S_{r}\)(%)Saturation degree
t(s)Time
T(\(^{\circ }\)C)Shallow ground temperature
\(T_{0}\)(\(^{\circ }\)C)Average ground surface temperature over a year
\(V_{a}\)(\(\text {m}^{3}\))Volume of air in ground
\(V_{s}\)(\(\text {m}^{3}\))Volume of solid soil in ground
\(V_{T}\)(\(\text {m}^{3}\))Total volume of ground
\(V_{v}\)(\(\text {m}^{3}\))Volume of void in ground
\(V_{w}\)(\(\text {m}^{3}\))Volume of water in ground
w(%)Gravimetric water content
z(m)Ground depth
  1. (−) signifies no unit