White Light Flat Fields -- No Sensitivity Change
Since early in the TRACE mission accurate flat fields in white light (WL) have been derived from a set of out-of-focus WL images of quiet granulation taken at various spatial displacements from the first image, at intervals of about 2 to 4 months. The images have been processed into a flat field using the Kuhn-Lin algorithm. The WL flat field images have not changed by more than +/- 1.5 % over the mission to date. The lack of sentivity change can apparently be explained if the blue photons in the white light image reach deeper to undamaged lumogen, which coats the face of the CCD. Each flat field image includes small corrections for artifacts intrinsic to the CCD and telescope, as well as for dust shadows common to certain channels. There are two WL flat fields, one when the fused silica filter is used, which shows dust shadows, and another when it is not in the line-of-site of the telescope. The final flat field for each channel, except for the WL, is the product of the WL and a UV or EUV flat fields. A WL flat field taken on September 3, 1999 with the fused silica filter in the line-of-site can be seen in the figure below.
White Light Flat Field for Sep. 3, 1999.
Modified 20-Apr-2006 20:00
