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6.1.4 Periodic Noise

All raw IUE images suffer from periodic noise (Nichols-Bohlin 1988, Shaw 1989) which is constant in raw space. The noise has been found to be multiplicative in nature and ranging from 1% to 8% in amplitude; however, the particular periodicities present and the amplitude of the noise are camera specific. Due to geometric distortion, the periodic noise in the ITF will not, in general, align with the noise present in the science image, and therefore, the periodic noise has been filtered from the ITF images using a Fourier-filtering technique. For the SWP camera, noise spikes were filtered every 192 points in the line direction and every 16 points in the sample direction in frequency space. For the LWP camera, noise spikes were filtered every 12 points in the line direction and every 16 points in the sample direction. The noise features in the LWR camera are much larger (8%) than the other cameras; noise spikes every 192 points are filtered in both the line and sample directions.



Karen Levay
12/4/1997