
\documentclass[11pt]{article}

%----Need full path so tth picks up my shorthand definitions
\input /usr/local/teTeX/tex/latex/LLS_Custom/ASL_defs

%----tth parser knows about the following if
\newif\iftth

%----Use this if to generage \tthonly{} and \texonly{}
\newcommand{\tthonlyhtml}[1]{
\iftth 
\begin{html}#1\end{html}
\fi  
}

\newcommand{\tthonly}[1]{
\iftth #1 \fi  
}

\newcommand{\texonly}[1]{
\iftth\else
#1
\fi
}

%----Make float placement less restrictive
\renewcommand{\textfraction}{0.10}
\renewcommand{\topfraction}{0.90}
\renewcommand{\bottomfraction}{0.75}
\renewcommand{\floatpagefraction}{0.70}

%----Keep the top/bottom margins very small so 2 graphs/page
\setlength{\textheight}{9.5in}
\setlength{\topmargin}{-1.in}
\setlength{\oddsidemargin}{.375in}
\setlength{\evensidemargin}{.375in}
\setlength{\textwidth}{5.75in}

%----Needed for a white background for every section
%%tth: \begin{html} <BODY BGCOLOR="#FFFFFF">  \end{html}

%---------------------------------------------------------------------------

\title{AIRS Module 12 Test 549 M12 SRF with CO2 Results}

\author{Scott Hannon, L. Strow}\date{\today}

\begin{document}

\maketitle

% The hardcopy document needs URLs to the WWW copies
\texonly{
\fbox{
\parbox[c]{0.9\linewidth}{
\begin{small}
\noindent This document is available on the World Wide Web:
\begin{description}
\item [Html: ]
  \textsf{http://asl.umbc.edu/pub/hannon/airs/fts/t549/t549_m12.html}
\item [Pdf: ]
  \textsf{http://asl.umbc.edu/pub/hannon/airs/fts/t549/t549_m12.pdf}
\item [Postscript: ]
  \textsf{http://asl.umbc.edu/pub/hannon/airs/fts/t549/t549_m12.ps}
\end{description}
\end{small}
}}
}

%\tableofcontents

%\listoffigures

%\begin{abstract}
%\end{abstract}

\section{Overview}

The test 549 data consists of Bruker SRF measurements with around 5 torr
of room temperature CO2 in the transfer optics.  This results in a
quasi-transmittance spectra of CO2 being superimposed upon the SRFs.
The CO2 features thus provide an absolute frequency standard which we
can use to determine the true measured frequency points.

Only 10 of the channels in module 12 showed distinct CO2 lines in the
measured SRFs; these were the only channels that we fit.  The data was
modeled for each channel by multiplying a calculated AIRS SRF (based upon
our best fit of the test 386 average SRF) by a monochromatic CO2 spectra,
and then convolving with the Bruker self apodization response for a 3.5023 cm
OPD with a 1.94 degree field of view.  The modeled self apodization handles
both the broadening of the SRF and the frequency shift to smaller wavenumbers.
The fit determined the best channel center frequency as well as the residual
frequency shift needed to match the frequency calculated directly from the
Bruker data (using a laser frequency of 15798.3064 cm-1).  We also let the
SRF width and a CO2 transmittance depth scale factor float.

Note: the Bruker interferogram data was zero-filled from 3.5 to 9.3 cm.
This results in a point spacing of ~0.053 cm, which is around 2.6 times more
fine than the true resolution.

The figure below is an example of the fit of one of the 10 channels.  The
CO2 line is clearly visible as a notch in the right side of the SRF.

\begin{center}
\begin{figure}
\includegraphics[width=0.9\textwidth]{t549_m12_ex_srf_fit.eps}
\caption{Example of Fit of SRF with CO2}
\tthonlyhtml{</A> <a href="t549_m12_ex_srf_fit.eps">Postscript version of
figure.</a>}
\end{figure}
\end{center}

\section{Results}

The residual frequency shift needed to match the the frequency calculated
using the Bruker laser frequency is shown below.  The Bruker frequency
is around 0.017 +- 0.009 cm-1 too big.  We are unsure how to explain this
discrepancy.  It is posssible our fits are not as good as we think; 0.017 cm
is only around 12\% of the true measured point spacing.  Another possiblility
is that the field of view angle was smaller than 1.94 degrees. However, the
angle would have to be 1.58 degrees to match our fit, and that is perhaps
well outside the estimated uncertainty in the angle.  One other possiblity
is a small error in the Bruker laser frequency.  A laser freqency of
15797.929 cm-1 would match our fit.


\begin{center}
\begin{figure}
\includegraphics[width=0.9\textwidth]{t549_m12_freqshift.eps}
\caption{Residual Freq Shift}
\tthonlyhtml{</A> <a href="t549_m12_freqshift.eps">Postscript version of
figure.</a>}
\end{figure}
\end{center}

%---------------------------------------------------------------------------

\end{document}

%%tth: \begin{html} <BODY BGCOLOR="#FFFFFF">  \end{html}

