Fig. 11
Optical flashes recorded by one of the two photodiode detectors on the C/NOFS satellite (downloaded from https://cdaweb.sci.gsfc.nasa.gov/index.html/). The top panel shows data for the lowest (most sensitive) threshold brightness—flashes are only detectable in the gray eclipse periods. The counts are the number of samples (~ 4000) per 0.5 s integration period that exceed a flux threshold, here 0.23 mW/m2—count rates are as high as a couple of hundreds. The bottom panel concatenates several eclipse periods together into an observation comparable in length with Hansell et al.’s (1995) telescopic Venus survey which detected seven flashes in about 4 h. With a 100 times higher threshold than the top panel, only a handful of counts are now obtained, and periods of 2 h or more exist with no counts at all (note that the instantaneous field of view of this sensor is only ~ 1000 × 2000 km)