Joint experiments were organized or available during stratospheric flights of a photopolarimeter, referred to as RADIBAL (radiometer balloon). In May 1984, RADIBAL flew simultaneously with another balloon-borne experiment conducted by the Institut d'A¿ronomie Spatiale de Belgique (IASB), which provides multiwavelength vertical profiles of the aerosol scattering coefficient. At this time, the El Chichon layer was observable quite directly from mountain sites. A ground-based station set up at Pic du Midi allowed an extensive description of the aerosol optical properties. The IASB and the Pic du Midi observations are consistent with the aerosol properties derived from the RADIBAL measurement analysis. The ability of RADIBAL to retrieve the vertical profile of the aerosol extinction coefficient was also demonstrated during a winter arctic campaign by comparison to Stratospheric Aerosol Measurement (SAM II) data and to airborne lidar data. As a result, RADIBAL appears to be a good candidiate for in situ validations of the Stratospheric Aerosol and Gas Experiment (SAGE II) and its derived products. ¿American Geophysical Union 1992