\begin{table}%t2
\par
\caption{\label{table:IRDC18223}Comparison of the different observational techniques for IRDC~18223-3.}  
%\centerline
\begin{tabular}{l c c c c}        
\hline\hline
\noalign{\smallskip}
Data &  Resolution &  Column density& Optical depth& Contrast   \\
 & (arcsec)  & (10$^{22}$ cm $^{-2}$) & at 8~$\mu$m & ($I_{\rm bg}/I_{\rm IRDC}$)  \\
\noalign{\smallskip}
\hline
\noalign{\smallskip}
8~$\mu$m GLIMPSE &  3  & 2.3 & 0.95&2.5 \\
1.2 mm IRAM$^{{a}}$&  11   & 5.9  & 2.4 &11 \\
3.2 mm PdBI$^{{b}}$     &  5\farcs8 $\times$ 2\farcs4 & 45  & 19 & 1.8e+08 \\
1.3 mm SMA$^{{c}}$ &  1\farcs3 $\times$ 1\farcs4 & 93 & 40  &1.8e+17 \\
\noalign{\smallskip}
\hline                                  
\end{tabular} 
\par
\smallskip
$^{{a}}$ \citet{2002ApJ...566..945B};
$^{{b}}$ \citet{2005ApJ...634L.185B};
$^{{c}}$ Fallscheer  et~al.~(2009, in preparation).
\par
\end{table}