Fundamental equations

Module core contains the fundamental equations of converting neutron counts to soil moisture.

corrfact_baro	Compute correction factor for barometric effects.
corrfact_vapor_rosolem	Correction factor for vapor correction from absolute humidity (g/m3).
n_to_theta_desilets	Convert neutron counts to theta.
horizontal_weight_zreda2008a	Horizontal weights according to Zreda et al.
horizontal_weight_zreda2008b	Presented by Bogena et al.
rescale_r
horizontal_weight_koehli	Horizontal weights presented by Koehli et al.
horizontal_weight_koehli_approx	Approximation adopted from Appendix B of Schroen et al.
penetration_depth_franz	Vertical penetration depth as a function of theta.
vertical_weight_franz	Based on Franz et al.
D86	Penetration depth, or rather the depth within which 86 % of neutrons probed the soil.
vertical_weight_koehli	Vertical weights for gven distance, depth, and environmental conditions.