A Practical Guide to Simulating Continuum Absorption in Earth’s Atmosphere

This third paper in our “Practical Guide” series demonstrates how to calculate continuum absorption by selected trace and major gases in Earth’s atmosphere. It complements our previous paper on simulating absorption in spectral lines (pronounced, sharp spectral patterns) using HITRAN with AFGL/MODTRAN height profiles. Here, “continuum” refers to relatively spectrally-smooth absorption features not included in HITRAN’s line-by-line (LBL) database. We focus on illustrative examples of different types of continua: O 2 -Air and O 4 for collision-induced absorption (CIA), O₃ and NO₂ as non-CIA examples, and H₂O, which is CIA-based but relies on the MT_CKD model. Spectrally, our examples are within the PACE OCI hyperspectral range (300-900 nm), but the principles and discussion are general. Unlike our published “Guides” on multiple scattering and LBL absorption, this one involves minimal coding, which justifies the epigraph. However, we embed Python snippets in the text, still aiming to facilitate the reader’s rapid transition from equations and datasets to coding.