NASA GSFC mascon solutions

Solution name Format Description Region
GSFC_global_mascons_v02.2 HDF5 ASCII Standard solution:
  • Comparable to GRACE Project Level-2 spherical harmonics (GSM) with post-processing corrections applied
  • Current span: Jan 2003 - Mar 2016
  • Iterated to convergence [Luthcke et al., 2013]
  • Background static field: EIGEN-6C with epoch of 2008.0
  • Tide model: GOT4.7 to degree/order 90 [Ray 1999]
  • Atmosphere and ocean de-aliasing: ECMWF+MOG2D [Carrere and Lyard, 2003]
  • Geocenter correction is applied [Swenson et al., 2008]
  • C20 is replaced with GRACE TN-07 [Cheng et al., 2013]
  • C21/S21 values are corrected following [Wahr et al., 2015]
  • Mascons are anomalies to the mean over 2004.0 - 2016.0
  • Small 161-day signals from S2 tidal aliasing [Ray and Luthcke, 2006] are removed
  • Wiener filter applied [Loomis and Luthcke, 2014]
  • The Antarctic Ice Sheet mascons for July 2015 are determined with temporal interpolation due to spatial gaps in the GRACE observations
  • Applications: Terrestrial water storage and cyrosphere after removal of GIA
Global
GSFC_global_mascons_v02.2-ICE6G HDF5 ASCII ICE6G GIA model removed [Peltier et al., 2015]
  • Applications: Terrestrial water storage and cyrosphere
Global
GSFC_global_mascons_v02.2-GeruoA HDF5 ASCII GeruoA GIA model removed [A et al., 2013]
  • Applications: Terrestrial water storage and cyrosphere
Global
GSFC_global_mascons_v02.2+ECMWF+MOG2D HDF5 ASCII ECMWF+MOG2D atmosphere and ocean de-aliasing model restored Global
GSFC_ocean_mascons_v02.2_OBP-GeruoA HDF5 ASCII GAD restored and GeruoA GIA model removed
  • OBP product = Solution + [ECMWF + MOG2D] - GAC + GAD - GeruoA
  • Applications: Ocean bottom pressure
Ocean
GSFC_ocean_mascons_v02.2_SLA-GeruoA HDF5 ASCII GAD restored; mean atmospheric pressure removed; GeruoA GIA model removed
  • SLA product = Solution + [ECMWF + MOG2D] - GAC + GAD - mean[GAD] - GeruoA
  • Applications: Ocean mass, comparable to steric-corrected sea level anomalies
Ocean


Previous mascon versions: v01.0/v01.1


HDF5 format documentation: GSFC_mascons_HDF5_format.pdf


Forward models and the GSFC solution strategy:

Since the beginning of the GRACE mission it has been standard practice to apply atmosphere and ocean de-aliasing products when processing the Level 1B data in order to directly remove these high-frequency signals from the inter-satellite measurements and the distributed gravity solutions. [Luthcke et al., 2006] and [Sabaka et al., 2010] demonstrated the benefit of also modeling global hydrology towards a further reduction in the measurement residuals and the mitigation of signal leakage. The GSFC mascon estimation procedure leverages this strategy by modeling global hydrology (GLDAS/Noah), glacial isostatic adjustment (GIA) [Peltier et al., 2015], and the largest co-seismic events during the span of the mission [Han et al., 2013]. In practice what we actually estimate is a "Delta" to these forward models, meaning that the fundamental resolution of GRACE (300-400 km) is only limited to the portion of the gravity field that is not captured by the various models and datasets. We also employ solution iteration [Luthcke et al., 2013], where the estimated updates to the mascons are applied as corrections to the forward model for a subsequent processing of the Level 1B data. This iterative process maximizes the role of the GRACE data on the final solution and minimizes the possible influence of the signal covariance design. The final solution is equal to the sum of the iterated “Delta” and the global hydrology model that was applied in the initial processing step. Over land and ice the mascons describe the total variability in water content, and over the ocean we provide separate solutions for ocean bottom pressure and sea level anomalies. The global solutions are available with two different GIA model corrections, and we have elected to not restore the co-seismic signal.


De-aliasing products and ocean-only mascons:

The GSFC ocean bottom pressure (OBP) and sea level anomaly (SLA) products make use of the GAC and GAD, which are products distributed by the GRACE Project. Over the ocean, both the GAC and GAD contain the sum of the OMCT non-tidal ocean model and the ECMWF atmospheric variability. They differ in that the GAC contains the vertically integrated atmospheric mass variability required for precise orbit determination, while the GAD applies the atmospheric surface pressure as required to relate GRACE measurements to ocean bottom pressure. The definitions of GSM, GAC and GAD products are described by Bettadpur [2012] and Flechtner et al. [2014]. Ocean bottom pressure from GRACE Project spherical harmonics is computed by: GSM+GAD-GIA. The GSFC procedures currently apply a different ocean model (MOG2D) in the Level-1B data processing than the GRACE Project (OMCT). In order to provide ocean products that are consistent with other solutions, we must restore our own de-aliasing model (ECMWF+MOG2D) and then remove the GRACE Project de-aliasing model (GAC) prior to restoring the GAD. To produce a product (SLA) that is comparable to steric-corrected altimetry measurements of sea level anomalies, we must remove the spatial mean of atmospheric surface pressure over the ocean, which is equal to the mean of the GAD as the non-tidal ocean component conserves mass.


When using this data please cite:

Luthcke, S.B., T.J. Sabaka, B.D. Loomis, et al., 2013, Antarctica, Greenland and Gulf of Alaska land ice evolution from an iterated GRACE global mascon solution, J. Glac. 59(216), 613-631, doi:10.3189/2013JoG12J147.


Contact:

Scott Luthcke<Scott.B.Luthcke@nasa.gov>
Bryant Loomis<Bryant.D.Loomis@nasa.gov>


References:

  • A, G., J. Wahr, and S. Zhong (2013), Computations of the viscoelastic response of a 3-D compressible Earth to surface loading: an application to Glacial Isostatic Adjustment in Antarctica and Canada, Geophys. J. Int., 192, 557-572, doi:10.1093/gji/ggs030.
  • Bettadpur, S(2012), GRACE Level-2 Gravity Field Product User Handbook, GRACE 327-734 (CSR-GR-03-01), Center for Space Research, The University of Texas at Austin.
  • Carrere, L., and F. Lyard (2003), Modeling the barotropic re- sponse of the global ocean to atmospheric wind and pressure forcing- Comparisons with observations, Geophys. Res. Lett., 30(6), 1275.
  • Cheng, M. K., B. D. Tapley, and J. C. Ries (2013), Deceleration in the Earth's oblateness, J. Geophys. Res., 118, 1-8, doi:10.1002/jgrb.50058.
  • Flechtner, F., H. Dobslaw and E. Fagiolini (2014), AOD1B Product Description Document for Product Release 05, GRACE 327-750 (GR-GFZ-AOD-0001), GFZ German Research Centre for Geosciences, Department 1: Geodesy and Remote Sensing.
  • Han, S.-C., R. Riva, J. Sauber, and E. Okal (2013), Source parameter inversion for recent great earthquakes from a decade-long observation of global gravity fields, J. Geophys. Res. Solid Earth, 118, 1240-1267, doi:10.1002/jgrb.50116.
  • Loomis, B. D., and Luthcke, S. B., 2014, Optimized signal denoising and adaptive estimation of seasonal timing and mass balance from simulated GRACE-like regional mass variations, Adv. Adapt. Data Anal. 06, 1450003, doi:10.1142/S1793536914500034.
  • Luthcke, S. B., T. J. Sabaka, B. D. Loomis, et al., 2013, Antarctica, Greenland and Gulf of Alaska land ice evolution from an iterated GRACE global mascon solution, J. Glac. 59 (216), 613-631, doi:10.3189/2013JoG12J147.
  • Luthcke, S. B., H. J. Zwally, W. Abdalati, D. D. Rowlands, R. D. Ray, R. S. Nerem, F. G. Lemoine, J. J. McCarthy and D.S. Chinn (2006), Recent Greenland Ice Mass Loss by Drainage System from Satellite Gravity Observations, Science 314, 1286, doi:10.1126/science.1130776.
  • Peltier, W. R., D. F. Argus, and R. Drummond (2015), Space geodesy constrains ice-age terminal deglaciation: The global ICE-6G C (VM5a) model, J. Geophys. Res. Solid Earth, 120, 450-487, doi:10.1002/2014JB011176.
  • Ray, R. (1999), A global ocean tide model from Topex/Poseidon altimetry: GOT99.2. NASA Tech. Memo 209478.
  • Ray, R.D. and S.B. Luthcke (2006), Tide model errors and GRACE gravimetry: towards a more realistic assessment, Geophys. J. Int., 167, 1055-1059, doi: 10.1111/j.1365-246X.2006.03229.x
  • Sabaka, T. J., D. D. Rowlands, S. B. Luthcke, and J. P. Boy(2010), Improving global mass flux solutions from GRACE through forward modeling and continuous time-correlation, J. Geophys. Res., doi:10.1029/2010JB007533.
  • Swenson S., D. Chambers and J. Wahr (2008), Estimating geocenter variations from a combination of GRACE and ocean model output, J. Geophys. Res.-Solid Earth, 113(B8), B08410, doi:10.1029/2007JB005338.
  • Wahr, J., R. S. Nerem, and S. V. Bettadpur (2015), The pole tide and its effect on GRACE time-variable gravity measurements: Implications for estimates of surface mass variations, J. Geophys. Res. Solid Earth, 120, 4597-4615, doi: 10.1002/2015JB011986.

  • This work was supported by the NASA MEaSUREs Program.