IWV_GNSS - MAP-IO - STATION LEVEL 2

The objective of the MAP-IO program is to assess the feasibility of building an atmospheric and marine biology observatory on board the Marion Dufresne. This observatory aims to carry out atmospheric observations at the ocean-atmosphere interface and integrated on the atmospheric column over the entire globe with a focus of particular interest for the study of the Indian and Southern Oceans. The MAP-IO program is positioned in an observatory logic with four main objectives; (i) integration into international atmospheric and oceanic networks by providing high quality data on a region devoid of permanent observation, (ii) validating and calibrating space sensors and numerical weather forecasting models, (iii) monitoring global changes on the Indian and Southern Ocean and (iv) observation of atmospheric and biology phytoplankton variability over the Indian and Southern Oceans.

MAP-IO takes advantage of the scientific campaigns at sea planned by the FOF by exploring different poorly documented ocean areas and by increasing and completing the observation systems of the programs with additional measurements. The differentiation value of MAP-IO versus conventional scientific programs at sea, and that it relies on the regular rotations of the TAAFs by documenting the atmosphere and the ocean surface state over a wide variability of sea ​​and latitude conditions. These multi-year observations of the Indian and Southern Oceans make it possible to uniquely document the trends, the mechanisms of ocean-atmosphere exchanges and the atmospheric composition on a seasonal and interannual basis.

IWV (Integrated Water Vapor) contents are retrieved using Global Navigation Satellite Systems (GNSS) data acquired from R/V Marion Dufresne. ZTD (Zenith Troposphere Delays) are produced with Gipsy-Oasis II v6.4 software using GPS observations. The ZTD data (one estimate every 30 seconds) are converted to IWV using on-board pressure measurement and integrated mean temperature (Tm) computed from surface temperature measurement and Bevis's formula. More information about the post-processing can be found in Bosser et al., 2022, https://doi.org/10.3390/atmos13060903.

STATION LEVEL 2 corresponds to data at native time resolution validated by the PI.

This dataset is organized as follows:

```yyyy doy ZTD ZHD Tm IWV SIG_ZTD SIG_IWV```

with:
- `yyyy`: year
- `doy`: decimal day-of-year
- `ZTD` (m): Zenith Troposphere Delay estimates from the GNSS analysis
- `ZHD` (m): Zenith Hydrostatic Delay evaluated from on-board pressure measurement
- `Tm` (K): integrated mean temperature evaluated from on-board temperature measurement and Bevis's formula
- `IWV` (kg/m2): Integrated Water Vapor content
- `SIG_ZTD` (m): formal error on ZTD
- `SIG_IWV` (kg/m2): formal error on IWV