deletions | additions       diff --git a/untitled.tex b/untitled.tex  index d54b80e..ea43df5 100644  --- a/untitled.tex  +++ b/untitled.tex 
...
\section{Introduction}  The added value of stable isotopes to interpret atmospheric hydrology has been of recent interest following the introduction remote sensing products, in-situ measurements and increasingly sophisticated models. In-situ measurements provide point measurements with good temporal coverage and resolution, but due to small scale of some of the processes influencing stable isotopes, it can be difficult to evaluate regional and global climate models. Satellite based remote sensing products have the potential to provide datasets with appropriate spatial scales but with poor temporal resolution, and although there have been recent attempts to assess the accuracy of these techniques only a couple use well calibrated in-situ measurements. To date only a couple of assessments of dataset accuracy have been provided using well calibrated in-situ measurements from aircraft platforms \cite{Herman_2014, Schneider_2015}. Beyond these studies assessment dataset accuracy has focused on using ground based remote sensing Fourier Transform Spectrometers (FTS), however, these have been shown to suffer from large measurement biases \cite{Schneider_2015}. There is a need to both provide validation studies of these ground based FTS measurements and to evaluate a broader range of products used to study water isotopes in the hydrological cycle.  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} The 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 Unlike surface based platform. They showed large positive biases for FTS retrievals. No similar comparison with  in-situmeasurements, ground based total column  measurements can be readily compared against has been conducted for  the satellite sensing products as they provide total column measurements similar to TCCON network, although  the GOSAT and SCHIMACHY satellite products, and for TCCON stations have been used to determine  the MUSICA project profile information can be retrieved for comparison against accuracy of a number of  satellite products sensitive to different altitudes. \cite{Frankenberg_2013, Scheepmaker_2015, Boesch_2013}.  These are sutiable for comparison - Ground based remote sensing - why is it useful (validation of satellites and can be more easily calibrated using in-situ measurements)  - what datasets are there (NDACC and TCCON (Wunch 2010))  - if at all how have they been calibrated.