Index: trunk/doc/modules/ModulesSDRS.tex
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--- trunk/doc/modules/ModulesSDRS.tex	(revision 5077)
+++ trunk/doc/modules/ModulesSDRS.tex	(revision 5359)
@@ -1,3 +1,3 @@
-%%% $Id: ModulesSDRS.tex,v 1.59 2005-09-20 22:01:33 jhoblitt Exp $
+%%% $Id: ModulesSDRS.tex,v 1.60 2005-10-18 14:07:17 eugene Exp $
 \documentclass[panstarrs,spec]{panstarrs}
 
@@ -1204,4 +1204,52 @@
 \item \code{MASK.NAME} (STR): Name of mask image
 \end{itemize}
+
+\subsection{Fringes}
+
+Some images contain a signal caused by thin-film interference in the
+device due to strong emission lines.  The resulting instrumental
+effect consists of a pattern (the fringe pattern) of bright and dark
+bands corresponding to the constructive and destructive interference
+of the emission lines.  In the case that a single emission line causes
+the line structure, the resulting pattern can be described by two
+independent parameters: First, the amplitude of the emission line
+determines the overall amplitude of the pattern.  Second, the
+three-dimensional surface structure of the device determines the shape
+of the pattern.  In a typical situation, the device is not only
+illuminated by the emission line (or lines), but also by a continuum
+spectral source, which contributes to the overall light detected by
+the device without following the fringe pattern.  The relative
+intensities of the continuum background and the fringe pattern depend
+on the device structure (thickness) and on the ratio of the continuum
+and line emission fluxes.  
+
+A simple approach to the fringe pattern is to subtract a master fringe
+frame scaled by the amplitude of the fringe pattern.  We thus need a
+method of measuring the fringe amplitude which is robust in the
+presence of stars and which is fast.  We implement a method used at
+CFHT in which the fringe pattern is mapped by a series of points pairs
+which correspond to peaks and valleys of the fringe pattern.  We
+define the following function to measure the global fringe amplitude
+of an image given a collection of fringe point pairs.
+\begin{prototype}
+stats *pmFringeStats (psImage *image, psArray *fringePoints, psMetadata *config);
+\end{prototype}
+This function measures the robust median at each of the minimum and
+maximum coordinates and determines the difference and mean of the two
+values.  From the collection of differences, the robust median is
+calculated, and returned as part of the fringe statistics.
+ 
+The \code{fringePoints} are defined by the following structure:
+\begin{datatype}
+typedef struct {
+    double xMin;
+    double yMin;
+    double xMax;
+    double yMax;
+    double delta;
+    double midValue;
+} pmFringePoint;
+\end{datatype}
+
 
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