Top: SO spectrum at 346.528 GHz for observation #313 at the disk center on November 15, 2011 (black solid line). Bottom, left: SO profile obtained from the depleted first-guess profile (red). SO profile obtained from the rich first-guess profile (blue). Final SO profile obtained from the intersection of the first two above ~ 90 km (orange). Dashed lines are respectively the depleted (red) and the rich (blue) a priori profiles. Bottom, right: Functional derivatives as function of altitude for observation #313 on November 15, 2011 at frequencies: ν_i = 346.528 GHz (red line); ν_i = 346.529 GHz (blue line); ν_i = 346.538 GHz (green line).