Upper panels: univariate Maxwellian distribution, with parameter σ = 8, is shown with a solid line in all upper panels; black squares connected by dashed lines represent the mean of the n_MC = 1000 samples of Tikhonov regularization. Results are for: n_s = 30 with σ_ϵ = 0.5 (upper left), n_s = 100 with σ_ϵ = 1 (upper center) and n_s = 1000 with σ_ϵ = 2 (upper right). Lower panels: bivariate Maxwellian distributions are shown by a solid line in all lower panels, with parameters σ₁ = 5 and σ₂ = 15 and amplitudes A = 0.7 and B = 0.3. Black squares connected by a dashed line show the estimated PDFs obtained by Tikhonov regularization. Results are for: n_s = 30 with σ_ϵ = 0.5 (lower left), n_s = 300 with σ_ϵ = 1 (lower center) and n_s = 1000 with σ_ϵ = 2 (lower right).