H_N = \sqrt{\frac{a_e \, A_T }{\pi}} \, \ln \frac{\delta T_A }{\delta T_{\rm cut} }

where

	true vertical depth of the Neutral Temperature Layer with reference to the Earth's surface
	Local average Thermal diffusivity of the soil between Earth's surface and NTL
	Period of annual temperature variation cycle:
	Annual average Earth's surface temperature variation in a given location based on weather reports
	Temperature measurement threshold (usually )

See Also