The CDR-derived Wet Tropospheric Correction (WTC) Product V2 is generated from the Level-2+ along-track altimetry products version 2024 (L2P 2024) distributed by AVISO+ (www.aviso.altimetry.fr). It provides a long-term, homogenized estimation of the wet tropospheric correction based on Climate Data Records (CDRs) of atmospheric water vapour combined with high frequencies MWR data.

Two independent CDRs datasets are used:

- REMSS V7R2 (coverage until 2022)

https://www.remss.com/measurements/atmospheric-water-vapor/tpw-1-deg-product/

- HOAPS V5 precursor CDR from EUMETSAT CM SAF (coverage until 2020) HOAPS V4/V5 data available via https://wui.cmsaf.eu

Note: the HOAPS V5 precursor is not yet an official CM SAF product; full validation and public release are pending.

The MWR/CDR WTC V2 estimates is derived using spatially varying but temporally constant polynomial coefficients (ai).

1. WTC V2 – Along-track L2P Product

Data format: The WTC V2 product is delivered in Level-2+ (L2P) format, along the satellite ground track. Each mission is distributed as a compressed archive (.tar.gz) containing one NetCDF4 CF-1.8 file per mission cycle.

Archive naming convention:

<mission>_WTC_from_WV_CDR_<version>.tar.gz

mission: TP (TOPEX/Poseidon), J1, J2, J3

version: product version (currently V2)

File naming convention inside archives:

<mission>_C<cycle>.nc

cycle: 4-digit cycle index (e.g., C0001)

Each NetCDF file contains: 1/ Along-track WTC estimate; 2/ Ancillary information; 3/ Space–time coordinates

2. WTC CDR Uncertainties – Gridded Product: A complementary product is provided, delivering regional trend estimates and associated uncertainties from the WTC Climate Data Record.

The uncertainty product is distributed as a single NetCDF4 file: wtc_trend_uncertainties.nc . This file contains global gridded fields of WTC CDR trend and uncertainty parameters.

Product content:

This is the first dedicated version providing both: WTC CDR (HOAPS) linear trends, and Uncertainty estimates on these trends. Uncertainties are expressed as 1-sigma confidence intervals, and propagated using the methodology described in Section 2.3 of the Product User Manual.

The product includes:

- Total uncertainty on the WTC trend, propagated from all identified uncertainty sources in the WTC–TCWV regression.

- Individual contributions of uncertainty sources (Uncertainties on regression coefficients: a0, a1 and their standard deviations; Uncertainties inherited from the HOAPS TCWV CDR)

These fields enable users to assess the relative importance of each uncertainty component and recompute uncertainty propagation with alternative methods.

Included regression input variables:

To ensure transparency and reproducibility, the product provides: 1/ regression coefficients a0, a1; 2/ their associated uncertainties (std of a0, std of a1); 3/additional diagnostic fields required to recompute uncertainties if needed.