The Portable Auroral Imager Observations

      Dayside Thin Filamentary Auroral Structures

      Features of less than a hundred meters across (105 km altitude) are seen in the original footage (105 mm lens, f/1.8). The aurora is here observed in the zenith with a temporal resolution of about 1 second (subsampled). Exposure time is 17 ms. Note that these images have been shrunk considerably for bandwidth purposes, making it hard to make out spatial detail (and SMPTE time stamps). The white spots are stars. Stars of magnitude down to about 9.8 are seen in the original footage.

      It should be evident that extremely short exposure times and high angular resolution are required to avoid smearing of thin auroral sheets. This explains the need for an image intensifier, long focal length lenses (up to 1600 mm in the case of the PAI), and precise alignment of optical axis with the local magnetic field.

      XX001-LYR-III

      BACK UP