|Documentation > SXT Observation Notes > this page|
Image name: Filter_mesh_effects.png (click image to enlarge)
Image size: 390.858 KB (1024x512)
Date submitted: 11-Nov-1994
SHADOWING BY SXT ANALYSIS FILTER SUPPORT MESH LWA 4/11/94 The SXT analysis filters (except for Be) are supported by stainless steel mesh with a square pattern and approximately 80% transmission. The mesh wires are about 35.6 micrometers wide and the pitch (repeat interval) of the mesh is approximately 360.7 micrometers. The x-ray image of a point source at the position of the filter is an annulus of roughly 11 mm diameter and width 17 micrometers, broken by the shadows of the "spider" of the entrance windows at 12 locations. For different positions in the SXT field of view this annulus will fall on the x-ray filter at different locations and be partially blocked by the wires of the mesh. It is this modulation, which Barry LaBonte calculates to be approximately 2%, which produces the square shadow pattern in the portions of the image illuminated by x-rays. This is illustrated by the highly processed sub image (in the upper inset) of a portion of the image above the SE limb where x-rays dominate straylight. Superposed upon the square x-ray grid shadow is a pattern of lines which are the one-dimensional shadows of the mesh wires cast by visible light which is transmitted by the thin aluminum filter at about a 1e-7 level. This solar image comes in through the failed entrance filter. The visible image is better focussed in one direction than the other because the entrance aperture of the x-ray mirror is only 350 microns radially whereas a 30 degree sector of the entrance filter provides about a 5 cm aperture in the circumferential direction. The 1-d shadow is illustrated in the bottom inset--is taken from the south coronal hole region where the x-ray signal is very small.