On 12 February 2000, before the cover of the Multi-angle Imaging SpectroRadiometer (MISR) opened for the first time, some "dark current" data was acquired to assess instrument performance. The image at left represents 41 seconds of data taken during a passage through the South Atlantic Anomaly (SAA), a region of Earth's upper atmosphere having a high concentration of charged particles. The bright points are signals created by these particles, which are mostly protons. About 1 pixel in 1000 is affected by the random "hits", a rate that drops to about 1 in a million outside the SAA, as had been expected.
The image at right contains the same data but with the contrast greatly enhanced. In addition to the "salt and pepper" pattern, random, dark horizontal stripes appear. When a proton creates a signal, it can trigger the camera video circuitry to temporarily darken the background level. This shows up as a stripe. The brightness of these stripes is typically less than 0.5% above the average background level with the camera cover closed.