Altitude profile obtained with UVES and method 3. The left vertical axis is the measured altitude, set to 23.8 km at [4520–4540] Å. The right vertical axis is the corrected altitude, if one considers the lowest region of h close to altitude 0 km and again h = 23.8 km at [4520–4540] Å. The horizontal dotted line represents the altitude 23.8 km. A 10 Å bin is superimposed in light-blue on the full-resolution profile, and a 100 Å bin in red is also shown, shifted upwards for clarity. The profile for λ ≤  ≈ 4300 Å is not shown, because the very weak umbra signal induces noise in the altitude profile which becomes noisy and h unexpectedly decreases. Oxygen and water-vapour absorption spectra at arbitrary scale are shown.