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Hubble Space Telescope
Electronic Ghosts
(Mr. Staypuft, Ringing & Streaking)

Mr. Staypuft

Diagnostic

Called "ringing" and "streaking" by the IDT, this is ghost images appearing at congruent points to a bright source in one quadrant, in the other three quadrants. For example, if there's a bright source at pixel (58,143), then you may see ghost images around (186,143), (186,15), and (58,15). This is due to the pull-down of the power supply, which doesn't completely recover from reading a large number by the time its asked to read the next number (from the next quadrant). This can be minimized by using an earlier read in a multiaccum sequence, before the source has gone into saturation, but this solution loses some integration time. In some cases a whole row (or column, whichever way the "fast" read clocking runs) can be anomalously high. This is worse for extended targets than for point sources.

In this movie Mr Staypuft appears as more energy is put into the core of the brightest stars of the cluster as a NIC3 focus sweep progresses. This focus sweep was taken before the start of the NIC3 campaign of January 3, 1998.

Cure

Some aspects of this effect can be minimized by removal of an average of object free rows or columns (whichever is perpendicular to the fast read direction). This is especially efficacious if the average is made in the vignetted region (the bottom of the chip).