<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2 Final//EN"> <!--Converted with LaTeX2HTML 98.1p1 release (March 2nd, 1998) originally by Nikos Drakos (nikos@cbl.leeds.ac.uk), CBLU, University of Leeds * revised and updated by: Marcus Hennecke, Ross Moore, Herb Swan * with significant contributions from: Jens Lippmann, Marek Rouchal, Martin Wilck and others --> <HTML> <HEAD> <TITLE>Fringe correction</TITLE> <META NAME="description" CONTENT="Fringe correction"> <META NAME="keywords" CONTENT="vol2"> <META NAME="resource-type" CONTENT="document"> <META NAME="distribution" CONTENT="global"> <META HTTP-EQUIV="Content-Type" CONTENT="text/html; charset=iso-8859-1"> <LINK REL="STYLESHEET" HREF="vol2.css"> <LINK REL="next" HREF="node60.html"> <LINK REL="previous" HREF="node58.html"> <LINK REL="up" HREF="node55.html"> <LINK REL="next" HREF="node60.html"> </HEAD> <BODY > <!--Navigation Panel--> <A NAME="tex2html2169" HREF="node60.html"> <IMG WIDTH="37" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="next" SRC="icons.gif/next_motif.gif"></A> <A NAME="tex2html2166" HREF="node55.html"> <IMG WIDTH="26" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="up" SRC="icons.gif/up_motif.gif"></A> <A NAME="tex2html2160" HREF="node58.html"> <IMG WIDTH="63" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="previous" SRC="icons.gif/previous_motif.gif"></A> <A NAME="tex2html2168" HREF="node1.html"> <IMG WIDTH="65" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="contents" SRC="icons.gif/contents_motif.gif"></A> <BR> <B> Next:</B> <A NAME="tex2html2170" HREF="node60.html">Bad Pixel Correction</A> <B> Up:</B> <A NAME="tex2html2167" HREF="node55.html">Additional Processing</A> <B> Previous:</B> <A NAME="tex2html2161" HREF="node58.html">Illumination Corrected Flat Fields</A> <BR> <BR> <!--End of Navigation Panel--> <H2><A NAME="SECTION006104000000000000000"> Fringe correction</A> </H2> The fringe correction should be made from regions of really empty sky. For that the sky frames should be combined such that cosmic rays and faint stars are eliminated. Hereafter, by smoothing the frame determine the average intensity level and subtract this value for the frame. After all objects have been removed from this sky frame the frame is essentially zero except for the fringe pattern. The frame is scaled to the same exposure time as the science frame and then subtracted. Because the night sky lines are variable, matching the fringe amplitude to the one in the science frame may not be as straightforward as expected, but should be possible with robust estimation. <P> <BR><HR> <ADDRESS> <I>Petra Nass</I> <BR><I>1999-06-15</I> </ADDRESS> </BODY> </HTML>
