Thank you for your interest in the GRACE and GRACE-FO RL06 Mascon solutions from the Center for Space Research. The GRACE and GRACE-FO solution time series are provided as single NetCDF timeseries. The CSR RL06 mascons are available in two formats.
The solutions with all the appropriate corrections applied (GAD, GIA, C20, C30, degree1, etc) in equi-angular grids.
Seperate components files are also available for advanced users to undo the respective corrections
Mascon estimation solutions represented as spherical harmonic coefficients.
Note: CSR Version 02 Mascon grids are represented on an ellipsoidal Earth unlike the previous versions.
You can use the CSR RL06 GRACE Mascons Viewer to explore the CSR RL06M solutions. The viewer is built using Cesium (https://cesium.com). Within the web tool you can select the year/month of the solution, choose land/ocean grid, colorscale for the eq. water height projection, view the GRACE timeseries for each mascon etc. Note: This tool is only for exploration and not suitable for any scientific analysis.
Warning: The viewer runs in the browser with no server side processing and downloads large amount of data. Depending on your internet bandwidth and computer resources, it may take several minutes to load the mascon data on the globe or in some cases you may not be able to use the viewer at all.
Representation on Ellipsoidal Earth
The mass anomaly grids in CSR RL06 v02 mascons for the GRACE/GRACE-FO time variable gravity are represented on the ellipsoidal earth of semi-major axis of 6378.1363 km
CSR RL06 v02 mascon grids have been corrected for representation on ellipsoidal earth. The ellipsoidal correction for mass anomaly grid representation has been applied as described by Ditmar 2018 (https://doi.org/10.1007/s00190-018-1128-0). This correction was applied seperately for land and ocean to prevent any leakage of the land signal correction into the ocean.
GIA Correction : A glacial isostatic adjustment (GIA) correction has been applied based on the model ICE6G-D; Peltier, W. R., D. F. Argus, and R. Drummond (2018) Comment on the paper by Purcell et al. 2016 entitled An assessment of ICE-6G_C (VM5a) glacial isostatic adjustment model, J. Geophys. Res. Solid Earth, 122
GAD Correction : AOD1B 'GAD' fields represented in the original mascon geodesic grid is added back for oceaonographic studies.
Component Grids to Undo the Corrections
The following grids (NetCDF files) are provided for expert users to 'undo' corrections applied to the mascon grids provided above.
Please note that all the grids provided (including the corrected grids) are anomalies relative to 2004.0000 - 2009.999 mean baseline. If any user decides to undo any correction and apply their own corrections, they should compute the anomalies relative to the same mean baseline for their corrections before applying their corrections.
The Land and Ocean girds that accompany the CSR RL06 Mascon solutions (v02) are available for download below in NetCDF format. Please consider these land and ocean masks when defining the basin masks in order to minimize leakage along the coastline.
Spherical Harmonic representation of the mascon solutions
The mascon solutions estimated as the correction to the mean field (GGM05C) are provided for the expert users. The 'signal definition' of these fields are exactly the same as that of the RL06 GSM solutions represented as updates to GGM05C mean field. The estimates of the update to a mean field is referred to as GSU in the GRACE/GRACE-FO L2 handbook.
ie. RL06_GSU + GGM05C = RL06_GSM
These sperical harmonic fields are provided upto degree and order 720x720. Note that d/o 720 does not represent the resolution of the fields but only used to represent the mascons. The need for representing these solutions upto d/o 720 arrises from the fact that you need a very high degree and order expansion to represent the sharp discontinuities of the signals at the coastline.
New Mascon Grid : RL06 Mascon solutions uses a newly defined grid as compared to the RL05 version. In this new grid, the hexgonal tiles that span across the coastline are split into two tiles along the coastline to minimize the leakage between land and ocean signals.
Estimation resolution : The data are represented on a 1/4 degree lon-lat grid, but they represent the equal-area geodesic grid of size 1x1 degree at the equator, which is the current native resolution of CSR RL06 mascon solutions. The RL06 grid files were released as 1/4 degree (instead of 1/2 degree in the case of RL05) so that the coastlines as defined in the new RL06 mascon grid could be represented properly
Processing standards : CSR RL06 GRACE and GRACE-FO Mascons are estimated with the same standards as the CSR RL06 Spherical harmonics solutions using GRACE Level-1 observations. Please visit the RL06 processing details page
Regularization : These mascon solutions are computed in presence of regularization constraint which is derived purely from GRACE and GRACE-FO information. No external model or data is used to inform the constraint matrix. Tikhonov regularization is used along with L-ribbon approach to compute the regularization parameter.
No empirical filtering : No additional smoothing or empirical de-striping or filtering applied to this data. The users should not apply any additional filtering or scaling factors to these solutions. These global solutions are not tailored towards a particular application and hence the solution set is applicable to all science areas of interest ie., oceanography, land surface hydrology, cryosphere, etc.
Anomaly baseline : The GRACE and GRACE-FO anomalies reported in these mascon solutions are relative to a 2004.0000 - 2009.999 mean baseline.
Resolution : Please note that while these solutions are estimated on a native resolution of about 120km wide cells, that is likely not the resolution of these GRACE/GRACE-FO solutions. The resolution of these solution is limited by the band-limited nature of GRACE/GRACE-FO. While we have not applied any implicit spatial smoothing, the users must exercise caution when using these solutions in basins smaller than approximately 200,000 km^2. Moreover, these solution should be used to perform basin level time-series analysis and never be used for analysis at a single grid point.
Representation on Ellipsoidal Earth : CSR RL06 v02 mascon grids have been corrected for representation on ellipsoidal earth of semi-major axis of 6378.1363 km. The ellipsoidal correction for mass anomaly grid representation has been applied as described by Ditmar 2018 (https://doi.org/10.1007/s00190-018-1128-0). This correction was applied seperately for land and ocean to prevent any leakage of the land signal correction into the ocean.
CSR RL06 Mascons solutions: Acknowledgement and Citation