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\wwwheader 
  {Exercise Results for Friday, June 1, 2001} 
  {http://asl.umbc.edu/pub/airs/exercises/friday.html}
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\section{Summary of Thursday}

We collected all sonde matchups that met Mitch's
clear flag.  We then subsetted from these those that were over ocean,
night only, and within a 1-hr match.  We then compared the B(T) at 900
\wn to B(T) at 2626 \wn, giving the scatterplot shown yesterday.
These matchups were put into an RTP file, the NCEP model was used to
extrapolate to levels where there was no sonde information, and then
the level RTP file was run through klayers to generate a layers RTP
file.  

These layer RTP files will be place on weather in
\texttt{/home/strow/Data/may29} after the teleconference, names TBD
(will email SCITEL).  We then ran SARTA and inserted the computed
radiances into the robs1 field in the RTP file.

\section{New work on Friday: \textbf{\textcolor{red}{UPDATE with TRUTH
      on June 07, 2001, new text in red}}}

Today we declared as clear only those matchups with abs(BT900 -
BT2616) $<$ 1K.  This left us with 16 matchups.  Examination of these
showed that 4 of them had \emph{very} different effective surface
temperatures, with obs-calcs of 10-20K.  We removed these from the
matchup list, which is fair because the NCEP model or AVHRR SST data
can be used to remove these outliers.  

The remaining 12 matchups looked pretty good, so I plotted their
location. See the following plot.

\begin{center}
\includegraphics[width=0.5\textwidth]{finalmatchmap.eps}
\end{center}

Note that we really only had 2 sonde matchups, and one of them is
above Alaska (7 FOVS).  So, we have ice, not ocean.  This was because
I used the landFrac flag.  I assume the NCEP ice flag will be set
here, so discrimination against this sonde should be easy as well in
the future.

Here is our final map of the sonde locations, and as already seen in
the previous plot, we've really only got 1 sonde match, with 4 FOVS
matching.  At least this plot shows the scan angles for this single
matchup.  

\begin{center}
\includegraphics[width=0.5\textwidth]{finalmatchmap1.eps}
\end{center}

The following graphs all show the same data, but with a variety of
zoom-ins.  The mean obs and calc B(T)'s are shown in the top of each
graph.  The bottom panel shows (1) the mean bias, (2) it's variance,
and (3) the mean bias if the NCEP model is used for the whole
calculation rather than the sonde data.  Note of course, that the
variance is pretty meaningless, since it is just the variability
between the 4 FOVs we matched.

This first plot is just an overview of the bias.  We do not do well
for high alititude channels since we have no truth there, as
expected (we do not know what Evan used to extend past the NCEP
model).  As we move from 650 \wn to higher wavenumbers, the bias
lowers to 1K where the sonde information should be good, and then goes
negative around 750 \wn.  It stays negative in the window region.
Ozone, of course, isn't too good.  

The water channels show a different sign for the sonde versus the
model, we are working to plot out the profiles right now to see why.
We will be doing statistics of model vs sonde next week in units of
radiance. This need investigation.  

In the near-IR very wild differences are seen at first, and (see later
plots) some extremely quick changes to the radiances that are
unphysical.  Finally, at the 2380-2400 \wn region the bias goes quite
positive again for channels sensitive to the upper atmosphere where we
have no information (I think).  Not that the bias in the 4 and 15
micron regions agree in the sense that, say, in the 4 micron region
the bias is at 2K when the B(T) is 240K, and you get the same result
at 15 microns, 2K bias when B(T) is 240K.  

I did not see any big jumps at array boundaries.

The final plot shows all channels, but with the bias scale zoomed in
so you can see that the surface biases are about the same, which I
required anyway.

In the future I will have to include water corrections (using the
sonde profile) and emissivity corrections to have a better
discriminator for clear.

\begin{center}
\includegraphics{bias1.eps}
\end{center}

\subsection{\textcolor{red}{650 - 1000 cm^{-1} Zoom}}

\textcolor{red}{The following graph shows the bias we observed with the single sonde,
followed with the ``true'' bias that we computed as follows.  The only
good sonde we found was in granule 98.  We read the L2Sup.Truth file
and plotted the clear flag, and found that in general the clear (over
ocean) FOVs were in the vicinity of the sonde.  The ``true'' bias was
then estimated by computing the mean difference between the biased and
unbiased radiances for the center FOV in each clear golfball.  The
variance of this mean was almost zero.  The second plot shows this
``truth'' bias.}

\textcolor{red}{Looks like we derived a fairly accurate bias in the CO2 temperature
sounding channels, but had the wrong sign of the bias in the window
region.  Our ``clear'' flag determination was quite crude, so errors
here are expected.  }

\begin{center}
\includegraphics[width=0.5\textwidth]{bias2.eps}
\end{center}

\begin{center}
\includegraphics[width=0.5\textwidth]{truthdbt4.eps}
\end{center}

\subsection{\textcolor{red}{1200 - 1600 cm^{-1} Zoom}}

\textcolor{red}{In this region the sonde bias had the same sign of the true bias, but
the true bias was significantly smaller.}

\begin{center}
\includegraphics[width=0.5\textwidth]{bias3.eps}
\end{center}

\begin{center}
\includegraphics[width=0.5\textwidth]{truthdbt3.eps}
\end{center}

\subsection{\textcolor{red}{2200 - 2700 cm^{-1} Zoom}}

\textcolor{red}{In this region the sonde bias had the same sign of the true bias for
the large excursions, as expected.  Again, our window bias is the
wrong sign, and about 10X too large.}

\begin{center}
\includegraphics[width=0.5\textwidth]{bias4.eps}
\end{center}

\begin{center}
\includegraphics[width=0.5\textwidth]{truthdbt2.eps}
\end{center}

\subsection{\textcolor{red}{2380 - 2395 cm^{-1} Zoom}}

\textcolor{red}{As at 15 microns, we recover the true bias with the sonde and model
data reasonably accurately.}

\begin{center}
\includegraphics[width=0.5\textwidth]{bias5.eps}
\end{center}

\begin{center}
\includegraphics[width=0.5\textwidth]{truthdbt1.eps}
\end{center}

\subsection{\textcolor{red}{Complete Bias, with Zoom of y-axis}

\begin{center}
\includegraphics[width=0.5\textwidth]{bias6.eps}
\end{center}



%\textbf{For the very busy reader, just look at the 
%        \textcolor{BrickRed}{text in dark red} 
%        to see the highlights/factoids.}

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