Examples of maps of the line depth ratio of the weak HDO transition (at 1344.90 cm⁻¹) to the CO₂ transition at 1345.22 cm⁻¹, recorded during the April 2019 run. Data are the same as in Figs. 3 and 6. The sub-solar point is shown as a white dot. Times refer to the mid-times of the observations. Data of April 21–24 are not shown because theterrestrial atmospheric absorption (see Fig. 3) is too strong for the HDO retrieval to be reliable.