<!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>Combining Sky Frames</TITLE> <META NAME="description" CONTENT="Combining Sky Frames"> <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="node49.html"> <LINK REL="previous" HREF="node47.html"> <LINK REL="up" HREF="node42.html"> <LINK REL="next" HREF="node49.html"> </HEAD> <BODY > <!--Navigation Panel--> <A NAME="tex2html2043" HREF="node49.html"> <IMG WIDTH="37" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="next" SRC="icons.gif/next_motif.gif"></A> <A NAME="tex2html2040" HREF="node42.html"> <IMG WIDTH="26" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="up" SRC="icons.gif/up_motif.gif"></A> <A NAME="tex2html2034" HREF="node47.html"> <IMG WIDTH="63" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="previous" SRC="icons.gif/previous_motif.gif"></A> <A NAME="tex2html2042" 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="tex2html2044" HREF="node49.html">Combine Example</A> <B> Up:</B> <A NAME="tex2html2041" HREF="node42.html">Preparing Your Calibration Frames</A> <B> Previous:</B> <A NAME="tex2html2035" HREF="node47.html">Combining Flat Fields</A> <BR> <BR> <!--End of Navigation Panel--> <H2><A NAME="SECTION00686000000000000000"> </A> <A NAME="ccd:combing-sky-frames"> </A> <BR> Combining Sky Frames </H2> The procedure is similar to the flat field combining procedure, except that you may want to scale the sky level using the mean, median or the mode of the intensity distribution or taking into account the exposure time. Hence, in the combining, like in the case of combining flat fields, correct weighting of the frame is important. Combining should be done filter by filter. See Table <A HREF="node48.html#ccd:sky-keywords">3.7</A> for the keywords. <P> <BR> <DIV ALIGN="CENTER"><A NAME="1902"> </A> <TABLE> <CAPTION><STRONG>Table 3.7:</STRONG> Keywords for combining sky calibration frames</CAPTION> <TR><TD> <DIV ALIGN="CENTER"> <TABLE CELLPADDING=3 BORDER="1" ALIGN="CENTER"> <TR><TH ALIGN="LEFT"><B>Keyword </B></TH> <TH ALIGN="LEFT"><B>Content </B></TH> <TH ALIGN="LEFT"><B>Default </B></TH> <TH ALIGN="LEFT"><B>Description </B></TH> </TR> <TR><TD ALIGN="LEFT"><TT> CCD_IN</TT></TD> <TD ALIGN="LEFT">input name</TD> <TD ALIGN="LEFT">?</TD> <TD ALIGN="LEFT">table of input frames</TD> </TR> <TR><TD ALIGN="LEFT"><TT> SK_TYP</TT></TD> <TD ALIGN="LEFT">descriptor value</TD> <TD ALIGN="LEFT">*</TD> <TD ALIGN="LEFT">exposure type to check, if any</TD> </TR> <TR><TD ALIGN="LEFT"><TT> SK_SIG</TT></TD> <TD ALIGN="LEFT">yes|no</TD> <TD ALIGN="LEFT">no</TD> <TD ALIGN="LEFT">create sigma image</TD> </TR> <TR><TD ALIGN="LEFT"><TT> SK_MET</TT></TD> <TD ALIGN="LEFT">comb. method</TD> <TD ALIGN="LEFT">avsigcl</TD> <TD ALIGN="LEFT">type of combining operation</TD> </TR> <TR><TD ALIGN="LEFT"><TT> SK_DEL</TT></TD> <TD ALIGN="LEFT">yes|no</TD> <TD ALIGN="LEFT">no</TD> <TD ALIGN="LEFT">delete cal. frames afterwards</TD> </TR> <TR><TD ALIGN="LEFT"><TT> SK_STA</TT></TD> <TD ALIGN="LEFT">mean|median|mode</TD> <TD ALIGN="LEFT">mode</TD> <TD ALIGN="LEFT">correct. by Mode/Median/Mean</TD> </TR> <TR><TD ALIGN="LEFT"><TT> SK_EXP</TT></TD> <TD ALIGN="LEFT">yes|no</TD> <TD ALIGN="LEFT">yes</TD> <TD ALIGN="LEFT">scale by exposure time</TD> </TR> <TR><TD ALIGN="LEFT"><TT> SK_SCA</TT></TD> <TD ALIGN="LEFT">yes|no</TD> <TD ALIGN="LEFT">no</TD> <TD ALIGN="LEFT">scale by MMM</TD> </TR> <TR><TD ALIGN="LEFT"><TT> SK_OFF</TT></TD> <TD ALIGN="LEFT">yes|no</TD> <TD ALIGN="LEFT">no</TD> <TD ALIGN="LEFT">add offset obtained from MMM</TD> </TR> <TR><TD ALIGN="LEFT"><TT> SK_WEI</TT></TD> <TD ALIGN="LEFT">yes|no</TD> <TD ALIGN="LEFT">yes</TD> <TD ALIGN="LEFT">use a weighted average</TD> </TR> <TR><TD ALIGN="LEFT"><TT> SK_SEC</TT></TD> <TD ALIGN="LEFT">area</TD> <TD ALIGN="LEFT">[<,<:>,>]</TD> <TD ALIGN="LEFT">area for computing MMM</TD> </TR> <TR><TD ALIGN="LEFT"><TT> SK_RAN</TT></TD> <TD ALIGN="LEFT">real,real</TD> <TD ALIGN="LEFT">-99999,99999</TD> <TD ALIGN="LEFT">valid pixel range</TD> </TR> <TR><TD ALIGN="LEFT"><TT> SK_CLP</TT></TD> <TD ALIGN="LEFT">real</TD> <TD ALIGN="LEFT">3.,3.</TD> <TD ALIGN="LEFT">low/high sigma clipping factor</TD> </TR> <TR><TD ALIGN="LEFT"><TT> SK_NUL</TT></TD> <TD ALIGN="LEFT">real</TD> <TD ALIGN="LEFT"><TT> NULL(2)</TT></TD> <TD ALIGN="LEFT">value for rejections</TD> </TR> </TABLE></DIV> <A NAME="ccd:sky-keywords"> </A> </TD></TR> </TABLE> </DIV> <BR> <P> <HR> <!--Navigation Panel--> <A NAME="tex2html2043" HREF="node49.html"> <IMG WIDTH="37" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="next" SRC="icons.gif/next_motif.gif"></A> <A NAME="tex2html2040" HREF="node42.html"> <IMG WIDTH="26" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="up" SRC="icons.gif/up_motif.gif"></A> <A NAME="tex2html2034" HREF="node47.html"> <IMG WIDTH="63" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="previous" SRC="icons.gif/previous_motif.gif"></A> <A NAME="tex2html2042" 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="tex2html2044" HREF="node49.html">Combine Example</A> <B> Up:</B> <A NAME="tex2html2041" HREF="node42.html">Preparing Your Calibration Frames</A> <B> Previous:</B> <A NAME="tex2html2035" HREF="node47.html">Combining Flat Fields</A> <!--End of Navigation Panel--> <ADDRESS> <I>Petra Nass</I> <BR><I>1999-06-15</I> </ADDRESS> </BODY> </HTML>
