The correlation between O- and X-mode reflectometer signalsis studied with a one- and two-dimensional reflectometer model in order to exploreits feasibilities as a q-profile diagnostic. It was found thattwo-dimensional effects and finite fluctuation levels both decrease the O-X correlation. At very low fluctuation levels, which are usuallypresent in the plasma core, there is a good possibility of determining the local magnetic field strength and use that as a constraint for the equilibrium reconstruction.