Structure inversions of the four target models using RLS, relying on oscillation modes with n = 10 − 50. The inferred buoyancy frequency difference is shown in orange (full line) and the difference between the models in blue (dashed line). The observational uncertainty is indicated by the light blue regions around the inferred profile. The inferred profile is discretized in 70 grid points, of which 50 are located in regions of the largest difference in buoyancy frequency, indicated by the red lines. The first row contains target models #1 and #2, while the second row contains target models #3 and #4. As in Fig. 13, the difference in oscillation frequencies between the target models is computed from the difference in structure and the kernels.