\begin{table}%T2
\caption{Methods of $\tau_0$ measurement.}
\label{tab:tau}
%\medskip
%\centering
\small
\begin{tabular}{ll l ll }
\hline\hline
\noalign{\smallskip}
Method & Measurables & $d$, m & Problems  & Reference \\
\noalign{\smallskip}
\hline \noalign{\smallskip}
SCIDAR & $C_n^2(h)$, $V(h)$ & $>$1 &  Needs large telescope  & Fuchs et~al. (\cite{SCIDAR}) \\ 
Balloons & $C_n^2(h)$, $V(h)$ & none &  Expensive, no monitoring & Azouit \& Vernin (\cite{Azouit}) \\
AO system & $r_0$, $\tau_0$  & $>$1 &    Needs working AO & Fusco et~al. (\cite{Fusco2004}) \\
SSS & $C_n^2(h)$, $V(h)$ & $>$0.4 & Low height resolution & Habib et~al. (\cite{Habib}) \\
GSM & $r_0$, $V$, $\tau_{AA}$ & $4\times0.1$ & No obvious relation to $\tau_0$ and $t_1$ & Ziad et~al. (\cite{GSM}) \\
MASS      & $\tau_0^*$ & 0.02 & Biased (low layers ignored) & Kornilov et~al. (\cite{MASS1}) \\
DIMM      & $r_0$  & 0.25 &  Indirect $\tau_0$ estimate & Sarazin \& Tokovinin (\cite{Sarazin2002}) \\
FADE  & $r_0$, $t_1$ & 0.35 & New method & This work \\
\hline
\end{tabular}
\end{table}