deletions | additions       diff --git a/section_Introduction_The_added_value__.tex b/section_Introduction_The_added_value__.tex  index 97b1b8f..60382fc 100644  --- a/section_Introduction_The_added_value__.tex  +++ b/section_Introduction_The_added_value__.tex 
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The ground based remote sensing of water isotopes has been performed through the Total Column Carbon Observing Network \citep[TCCON; ]{Wunch_2011} and the MUlti-platform remote Sensing of Isotopologues for investigating the Cycle of Atmospheric water (MUSICA) project using the Network for the Detection Atmospheric composition Change (NDACC) Fourier Transform Spectrometers \cite{Schneider_2012}. \citet{Schneider_2015} presented an evaluation of the accuracy of the MUSICA sites was provided through comparison against in-situ measurements of water vapour isotopes from an aircraft platform. They showed large positive biases for FTS retrievals. No similar comparison with in-situ measurements has been conducted for the TCCON network, although the TCCON stations have been used to determine the accuracy of a number of satellite products \cite{Frankenberg_2013,Scheepmaker_2015,Boesch_2013}.  \\  \\  Large positive biases consistent for all comparisons with in-situ observations \citet{Worden_2011, \cite{Worden_2011,  Herman_2014, Schneider_2015}. Comparison between satellite SWVI products and the TCCON network have shown the satellite illustrate a negative bias Risi \cite{Risi_2012, Boesch_2012}, whether this is caused by inaccuracy in the satellite or TCCON retrievals remains uncertain. \citet{Risi_2012} showed that whilst the TCCON column retrievals were enriched relative to $\delta$^2H from the SCHIAMACHY instrument, the latitudinal gradient was preserved. \citet{Boesch_2012} compared the TCCON isotope retrievals with the GOSAT satellite and showed the bias between the 2 datasets varied with season and location. They also showed that the largest biases were observed for the Darwin dry season. Clearly, there is a need to assess the accuracy of the TCCON measurements using accurate in-situ observations, consequently providing a measure of satellite retrieval accuracy.