Five smoke trails, the tallest being seven feet high, are moving to the right in the blast wave from 2500 tons of ANFO (ammonium nitrate/fuel oil). The shock front has passed out of the field of view. The trails have moved ahead of the launcher tubes, which have more inertia than the smoke particles. Also seen are a number of red and blue wooden blocks as they respond to the blast flow and four cantilever drag gauges starting to bend. The striped pole in the foreground and the hour glass on the wall in the background are photogrammetric reference points. The photographic and passive measurement techniques were used to monitor the boundary layer flow at the ground surface. The results obtained using the three techniques were compared to predictions from hydrodynamic calculations.
DM&A use cinematic photogrammetry to measure the distortions
of structures in blast waves. For example, the shape of the tall cantilever shown above
was examined in a sequences of film frames and the elastic and plastic modes of bending
studied. After the explosion the section of cantilever above ground remained straight and
appeared to have bent only at its base, but during the blast it was seen to bend in an
oscillating whip-like manner.