QUOTE (mcaplinger @ Sep 5 2006, 09:19 PM)
Ralph is TDI, but as far as I know, LORRI is just a framing camera, not a pushbroom. (And BTW, pushbroom and TDI mean different things.) This looks like a small amount of H register readout noise to me, but the noise level seems very low.
LORRI *IS* a frame camera. The streaks are more likely due to "hot" pixels and their distribution amongst the columns. That is, a column with more pixels with above average dark current will seem to have a bright streak in it. A column with fewer will seem to be a dark streak. As these bright and dark streaks are there in every frame, a "dark frame" can be recorded, for instance by pointing at a region of the sky with few stars, and removed from the science images in post processing. There are also variations in sensitivity between the individual pixels that can be corrected. That and a few other steps are what it takes to get the nearly flawless images we are used to seeing, like in the publication quality releases from Hubble.
TDI, or time delay integration, is a form of pushbroom scanning where there are parallel registers across the field of view. An "electronic image" of electrons stored in the array is formed in the first row as the optical image sweeps across it. This electronic image is clocked along at the same rate the image is being swept over the detector. As the optical image and electronic image move at the same speed (with the electronic image jumping from row to row) there is more time to build up an image. The MVIC arrays in Ralph so work in this fashion, with 32 rows of 5000 pixels each in each of six arrays. (Two "panchromatic" i.e. full spectrum for "black and white" images and four arrays filtered for color: Red, Blue, Near IR, and a band for detecting Methane.)