deletions | additions       diff --git a/section_Introduction_The_added_value__.tex b/section_Introduction_The_added_value__.tex  index 60382fc..283b80b 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 \cite{Worden_2011, Herman_2014, Schneider_2015}. Comparison between satellite SWVI products and the TCCON network have shown the satellite illustrate a negative biasRisi  \cite{Risi_2012, Boesch_2012}, whether this is caused by inaccuracy inthe  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. Theyalso  showed that the GOSAT retrievals were very sensitive to surface characteristics and the shape of the H_2O and HDO a priori column. Interestingly  the largest biases were observed for the Darwin dry season. Clearly, there is a need in Darwin, Australia where complex water vapour and isotope profiles would be expected due  to the strong vertical mixing in this tropical region. To better  assess the accuracy of errors associated with satellite based retrievals determined from these studies,  the TCCON measurements using would greatly benefit from comparisons against  accurate in-situ observations, consequently providing a measure of satellite retrieval accuracy. observations.