A liquid drop undergoes aerodynamic deformation and breakup when it is exposed into a gas stream. Many techniques were used to measure the size and velocity of the secondary droplets while quantifying the rim/ligament still remains a challenge. An automatic method to extract the 3D properties of the toroidal rim in the bag breakup was recently developed based on digital in-line holography (DIH). To reduce the uncertainty caused by the out-of-focus overlap, a DIH configuration with a slightly rotated view is adopted here. The entire rim is reconstructed by stitching all the sections together. Holograms are recorded with a high-speed camera operated at 20 kHz to study the dynamic evolution of the rim in the bag breakup of an ethanol drop. Both the 3D visualization and z -- y view reflect the rim's structure development within 5.2 ms. The rim expands followed with disintegration into ligaments and relatively larger droplets. The volume of the rim is measured ～ 95 % and that of the secondary droplets is ~ 5 % of the initial drop volume before rim breakup. Then the volume of rim/ligament decreases after rim breakup which on the other hand increases the volume fraction of secondary droplets. The total volume of the rim/ligament and fragments is very close to the initial drop volume in most measurements except when the instant swelling happens in local at-omization. Then the total measured volume decreases rapidly as the relatively large fragments move out of the field of view.
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