The MT surface impedance tensor has four components: Zxx, Zxy, Zyx and Zyy, which satisfy the impedance relations:
An inter-station MT impedance is a variant of the MT impedance, where the magnetic field $H_x$ and $H_y$ is obtained at a remote site,
where indices 1 and 2 indicate two different site locations.
See also MT impedance and interstation magnetic field transfer functions.
Egbert, G.D., 1997. Robust multiple-station magnetotelluric data processing. Geophysical Journal International, 130(2), pp.475-496.
Chave, A.D. and Jones, A.G. eds., 2012. The magnetotelluric method: Theory and practice. Cambridge University Press.