\documentclass[twoside,a3]{article}
\usepackage[silent,pdf,hyper]{elxfinal}
\usepackage{color}
\usepackage{multirow}
\usepackage{hyperref}
\textwidth=54pc
\textheight=90pc

\begin{document}
\thispagestyle{empty}
\begin{tabular}
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\hline
\\ [-7pt]
& \multicolumn{6}{c}{Free-Air Gravity (FAG)}  \\
& \multicolumn{3}{c}{Northern hemisphere} & \multicolumn{3}{c}{Southern hemisphere} \\
&   All values&  Positive&  Negative & All values & Positive & Negative \\
  [7pt]  \hline   \\ [-4pt]
FD min & 2.10  &      2.01  &    2.01   &    2.13    &    2.01   &   2.01  \\
FD max & 2.56  &      2.38  &    2.41   &    2.64    &    2.40   &   2.44   \\
$R^2$     & 0.908 &      0.968 &    0.967  &     0.975  &    0.994  &    0.990  \\
[7pt]  \hline   \\ [-4pt]
  & \multicolumn{6}{c}{Digital Elevation Model (DEM)}  \\
& \multicolumn{3}{c}{Northern hemisphere} & \multicolumn{3}{c}{Southern hemisphere} \\
&   All values&  Positive&  Negative & All values & Positive & Negative \\
[7pt]  \hline   \\ [-4pt]
 FD min &2.01    &    2.0   &    2.01   &      2.01   &   2.0    &    2.01 \\
FD max &2.64    &    2.45  &    2.58   &     2.58    &  2.47    &   2.54  \\
$R^2$     & 0.942  &     0.903&    0.940  &      0.857  &    0.863 &     0.910  \\
[4pt] \hline
\end{tabular}
\end{document}
