The JPL GRACE Mascon Ocean, Ice, and Hydrology Equivalent Water Height (hereafter, Mascon) products are now available as part of the Tellus MEaSUREs collection of Earth System Data Records (ESDRs). This data product differs from other GRACE data products in that the gravity field has been solved for in terms of equal-area 3-degree spherical cap Mascon solutions, rather than spherical harmonic coefficients. The data product contains monthly global water storage anomalies relative to a time-mean expressed on a 0.5 by 0.5 degree (latitude by longitude) grid, although the native resolution is still limited to 3 by 3 degrees.
Mascon has implemented a Coastline Resolution Improvement (CRI) filter to separate land and ocean mass anomalies from individual Mascon solutions that span coastlines. The CRI-filtered data is considered to be more user friendly and recommended for most use applications and can be found here:
Expert users who wish to access the data without the implementation of the CRI filter can do so here: https://podaac.jpl.nasa.gov/dataset/TELLUS_GRACE_MASCON_GRID_RL05_V1
The water mass anomalies for both datasets are given in equivalent water thickness units and contained within a netCDF file. The Mascon solution is derived from solving for monthly gravity field variations in terms of 4,551 equal-area 3-degree spherical cap mass concentration functions, rather than spherical harmonic coefficients. Additionally, realistic geophysical information is introduced during the solution inversion to intrinsically remove correlated error. Thus, these Mascon solutions do not need to be destriped or smoothed, like traditional spherical harmonic gravity solutions. The resulting Mascon product consists of 4,551 relatively independent estimates of surface mass change, a subset of which span coastlines and contain a mixture of land and ocean mass signals. Since the Mascon basis function acts as an inherent smoother on the gravity field, a set of optional gain factors (hereafter referred to as Scale Factors) can be applied to the solution to study mass change signals at sub-Mascon resolution; these Scale Factors and CRI-filtered land masks are also provided as unique netCDF files within the same data directory as the Mascon datasets. Note: Scale Factors are only applicable for terrestrial hydrology applications.
For more general information about the Mascon processing and usage guidance, please visit https://grace.jpl.nasa.gov/data/get-data/jpl_global_mascons/.
For a detailed description on the Mascon algorithm, including the mathematical derivation, implementation of geophysical constraints, and solution validation, please see Watkins et al., 2015, doi: 10.1002/2014JB011547.
Science Applications of Mascon data include:
- Quantifying groundwater depletion/accumulation rates
- Flood prediction
- Rate of mass loss/gain from glaciers and ice sheets
- Steric rate of sea level rise
- Ocean currents
- Solid Earth
- Glacial isostatic adjustment
Figure 1: Example of a spherical cap Mascon solution for 1 arbitrary month.
Figure 2: Mascon solutions depicted for 1 month over Greenland and North Atlantic region. Top image represents the unfiltered solution while the bottom image represents the CRI-filtered solution.
Figure 3: GRACE solution comparison of 2003-2012 trends in water mass (cm/year). Top image uses the CRI-filtered Mascon solution. Bottom image uses the JPL RL05 Harmonics, Destriped, 300 km smoothed solution. The California drought signal is more evident in the Mascon solution due to how the data are processed.