# 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 (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 (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 (TCCON; Wunch et al., 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 (Schneider 2012). Schneider et al. (2015) presented an evaluation of the accuracy of the MUSICA sites was provided through comparison against in-situ measurements of water vapor isotopes from an aircraft platform. They showed larg