Fig. 2
From: Imaging of polar cap patches with a low-cost airglow camera: pilot observations in Svalbard, Norway
Summary of the image processing, a raw image from the WATEC ASI at around 20:35 UT on December 4, 2013, b absolute optical intensity image from the EMCCD ASI obtained almost simultaneously, c average of seven raw images (total exposure time ~ 30 s) from the WATEC ASI, d average of 15 raw images (total exposure time ~ 1 min) from the WATEC ASI, e average of 30 raw images (total exposure time ~ 2 min) from the WATEC ASI, and f average of 75 raw images (total exposure time ~ 5 min) from the WATEC ASI