AN INSTRUMENTAL SOURCE FOR THE DARK PIXEL CLUSTERS IN THE POLAR VIS AND UVI EXPERIMENTS

The controversy over the observation of dark pixels by the DE-I and Po lar imagers has centered around the small-comet theory rather than an instrumental source to account for the dark pixels. To check for instr umental effects, we simulated the Polar VIS and UVI response to unifor m illumination and calculated the rate of dark pixel clusters. The sim ulation includes the finite size and exponential amplitude of light pu lses from the experiments' image intensifiers and the removal of conta mination by penetrating radiation. The dark pixel cluster size distrib utions from the computer simulations reproduce the distributions obser ved in both of the Polar imagers. (The VIS distributions were produced independently from one day of raw data kindly provided by Frank and S igwarth and from a world-wide-web catalog of atmospheric hole events p repared by Frank and Sigwarth from their own Polar data. These two set s of VIS distributions are in agreement with each other and with the c omputer simulations.) These instrumental effects fully explain the dar k pixel clusters without the need for invoking a geophysical phenomena .