Blended altimetry de-aliasing model, from a combination of DAC + GRACE swath data

These netcdf files contain an alternative version of the 1/4°-gridded, 6-hourly, Dynamic Atmospheric Correction (DAC) used in Jason altimetry.  The files are a combination of the original DAC's Mog2D ocean model, their Inverted Barometer (IB) model, and GRACE CSR-Swath data, as explained in JGR Ocean's "Using GRACE to improve altimetry’s ocean de-aliasing model" (2021) by Bonin and Save. 

The data was created via an EOF recombination.  The two products combined are: 

1.)  DAC ocean model + IB product:  This is Jason altimetry's Dynamic Atmospheric Correction (DAC), including the Inverted Barometer (IB) product.  The IB product is removed for the combination with GRACE, then restored again at the end.

2.)  GRACE CSR-Swath data:  This is an experimental mass concentration (mascon) product from the Center for Space Research, where mass change within those mascons under and near the GRACE groundtrack is measured, with information from multiple passes accumulated to estimate the global mass anomaly at daily, 1° resolution.  Gaps are filled via a combination of older local data and newer data from neighboring mascons, and a regularization technique is applied.

The EOF blending only occurs in the 10-20-day frequency band.  All other frequencies revert back to the DAC data.  Within the 10-20-day frequency band, EOF spatial patterns were derived from Mog2D*.  An EOF reconstruction based on least squares was run on these EOF mode maps, fitting the CSR-swath data to them.  This results in a CSR-swath-derived time-series for the same spatial patterns, which is directly comparable to the Mog2D* EOF time-series.  We used a comparison with Jason altimetry to determine, for each EOF mode, whether Mog2D* or CSR-swath better explained real data (and was thus a better de-aliasing model).

The file here is the combination of the "best" modes, plus the residual Mog2D* data from higher and lower frequencies, and the DAC's IB product restored afterwards.  It is designed for use ONLY as a de-aliasing product, not for general oceanographic use.