Spectrum of Mars between 1383.5 and 1390.0 cm^-1 (thick black line), integrated over the Martian disk, recorded with EXES (Ls = 113°, normalized radiance). Synthetic models of the Martian atmosphere: contributions from CO₂ (purple), H₂O (300 ppmv, blue), and HDO (467 ppbv, green). Thin black line (in absolute units shifted by −0.30): standard transmission from the terrestrial atmosphere, computed with the EXES model. The EXES spectrum shows an offset of 0.1 in the core of the strong water line at 1387.5 cm^-1, while the terrestrial atmospheric transmission is expected to be zero at this frequency.