Panel a: Herschel/SPIRE 250 μm emission image of a part of the Polaris cloud. The HPBW angular resolution is 182. Panel b: noise-subtracted and beam-corrected power spectrum of the image shown in panel a over the range of angular frequencies 0.025 arcmin⁻¹ <  k <  2 arcmin⁻¹. The red curve shows the best fit power-law model over this frequency range, which takes the form P_sky(k) = A_ISMk^γ + P₀ with γ = −2.63 ± 0.1. Panel c: residuals between the best-fit power-law model and the power spectrum data points (triangle symbols). The (see Eq. (10)) of the residuals is ∼0.03. The vertical dashed line marks the angular frequency k_fil ∼ (0.6/θ_fil) corresponding to a characteristic filament width of ∼0.1 pc.