Predicted integrated intensities f_ℓ(θ) as a function of $A_V^{\text{tot}}$ or G₀, with P_th = 10⁵ K cm⁻³. The white full line represents the standard deviation of the additive noise, σ_a,ℓ, from Eq. 15 for the ORION-B observations (Pety et al. 2017). The dashed white line indicates the standard deviation with a ten times longer integration time (deeper integration use case). The regions with integrated intensities lower than 10⁻¹² erg cm⁻² s⁻¹ sr⁻¹ are shown in white for better visibility of the higher intensities. The white rectangle on the first panel delimits the parameter space characterizing the Horsehead Nebula.