Spline-approximations for transport and thermodynamic nitrogen properties

Tables of transport and thermodynamic nitrogen properties computed by I. A. Sokolova in wide range of temperature and pressure are approximated by 2D tensor product splines. These approximations have the same accuracy as original tables (relative $l_2$ error ${\sim}1\%$, max error ${\sim}5\%$). They have less number of parameters and allow to obtain thermophysical coefficients at any temperature and pressure in the given range. Approximations may be used as a reference data. Simple program is included for the approximations to be readily involved in practice.