STScI Logo

Hubble Space Telescope
Image Persistence

Persistence
DARK exposure 32 seconds after bright illumination
Persistence
DARK exposure 512 seconds after bright illumination

Diagnostic

The persistence is the excess dark current observed immediately after the detectors have been saturated with bright light. Persistence tests have been performed with NICMOS during SLTV and SMOV. The results and analysis of these tests are presented in the following Instrument Science Reports and Posters:




The examples are images of dark current data obtained after the detectors have been flooded by a long exposure of 512 seconds where the selected star, Oph S1, is observed with the F160W filter and an over-exposure of 300 to 500 times linear full well are expected.

These images show the persistence to be present in data taken after the bright illumination for at least 60-120 seconds, followed by a slow decay where small persistence signatures are still visible after 10 minutes of dark exposures.

Cure

Care should be taken to not saturate the detectors, and observations of bright sources should be dithered by large amounts (e.g. between quadrants) to minimize problems with persistence. Vaguely extended bright patches may indicate a persistent image, and preceding exposures should be checked for objects in this area. Note that a persistent image will not move when an exposure is dithered.