\newcommand{\der}[2]{\frac{\partial #1 }{\partial #2} }

%termes lations
\def\ie{{\em i.~e.}}
\def\etal{{\em et~al.}}
\def\apriori{{\em a~priori}}
\def\apost{{\em a~posteriori}}
\def\afort{{\em a~fortiori}}
\def\etc{{\em etc.}}
\def\insitu{{\em in--situ}}
\def\adoc{{\em ad~hoc}}

\def\sc#1{Section~\ref{sc:#1}}
\def\an#1{Annexe~\ref{an:#1}}
\def\ch#1{Chapitre~\ref{ch:#1}}
\def\fg#1{Fig.~\ref{fg:#1}}
\def\fgs#1{Figs.~\ref{fg:#1}}
\def\eq#1{Eq.~\ref{eq:#1}}
\def\eqs#1{Eqs.~\ref{eq:#1}}
\def\tb#1{Table~\ref{tb:#1}}
\newcommand{\av}[2]{{\overline{#1}}^{ #2 }}
\newcommand{\avg}[1]{\left< #1 \right>}
\def\cd{C_D}
% definitions de Macros pour tout l'article
\def\co{$CO_2$}
\def\eq#1{Eq.~\ref{eq:#1}}
\def\fig#1{Fig.~\ref{fg:#1}}
\newcommand{\dep}[1]{\left( #1 \right) }
\newcommand{\depb}[1]{\left[ #1 \right] }
\newcommand{\depc}[1]{\left\{ #1 \right\} }
\def\coband{$CO_2\ 15\mu$m~band}
\def\ps{p_S}
\def\etal{{\em~et al. }}
\def\insitu{{\em in--situ }}
\def\t{\theta}
\def\dnw{^{\downarrow}}