Correcting Background Streaks in HST Wide Field Planetary Camera 2 Data

The Wide Field 4 (WF4) CCD of the Hubble Space Telescope Wide Field Planetary Camera 2 (WFPC2) has exhibited intermittent anomalous behavior seen as a low or zero bias level since early 2002. During these episodes, which occur every 4 to 6 hours, faint (< 1 DN rms) horizontal streaks appear in the CCD data. We present an algorithm designed to eliminate these streaks while preserving the photometry for the WF4 and the other chips. The algorithm uses data in the entire image to compute the correction to be applied. The routine is a stand-alone task intended to be used after all other corrections (for bias, dark, flat fielding and gain) have been performed. The program has been successfully tested with a variety of image types, such as stellar fields and extended sources. Default program parameters have been identified that work well for these cases, and the user also has the flexibility to change most of the input parameters. We discuss this algorithm, its application to WFPC2 data, and its potential application to other on-orbit CCD detectors.