Successful comparisons between VHF oblique (15 ø) radar echo profiles and reconstructed ones deduced from high-resolution temperature balloon measurements were presented by Luce et al. [1996]. The method was based on the evaluation of the threedimensional isotropic refractive index spectrum at the Bragg wavelength from the available temperature profiles ("spectral method"). However, the isotropic hypothesis is questionable, especially in regions where temperature sheets [Dalaudier et al., 1994] are observed. Indeed, the associated anisotropic temperature fluctuations should contribute to the onedimensional vertical temperature spectrum at small scales. In the present paper, another method, less sensitive to anisotropic contaminations, is used. This method is based on an