DOI: 10.5880/cost-g.gravis_01_l2b
title: Post-processed GRACE/GRACE-FO Geopotential GSM Coefficients COST-G RL01 (Level-2B Product)

description: Post-processed GRACE/GRACE-FO spherical harmonic coefficients of COST-G RL01 Level-2 GSM products representing an estimate of Earth's gravity field variations during the specified timespan. Post-processing steps comprise: (1) subtraction of a long-term mean field; (2) optionally, decorrelation and smoothing with VDK filter (anisotropic filter taking the actual error covariance information of the underlying GSM coefficients into account, see Horvath et al. (2018)); (3) replacement of coefficients C20 and C30 (only for the months within the period from 2016/11 through 2017/06) and its formal standard deviations by values estimated from a combination of GRACE/GRACE-FO and Satellite Laser Ranging (SLR); (4) subtraction of linear trend caused by Glacial Isostatic Adjustment (GIA) as provided by a numerical model; (5) insertion of geocenter coefficients (C10, C11, S11); and (6) removal of estimated aliased signal of the S2 tide (161 days period). These coefficients represent signals caused by water mass redistribution over the continents and in the oceans. 
 
 These post-processed GRACE/GRACE-FO GSM products are denoted as Level-2B products. 
 
 There are multiple variants of Level-2B products available that differ by the characteristics of the anisotropic filter applied. These variants are distinguishable by the following strings in the product file names: 
 
 - 'NFIL': Level-2B product is not filtered 
 - 'VDK1': Level-2B product is filtered with VDK1 
 - 'VDK2': Level-2B product is filtered with VDK2 
 - 'VDK3': Level-2B product is filtered with VDK3 
 - 'VDK4': Level-2B product is filtered with VDK4 
 - 'VDK5': Level-2B product is filtered with VDK5 
 - 'VDK6': Level-2B product is filtered with VDK6 
 - 'VDK7': Level-2B product is filtered with VDK7 
 - 'VDK8': Level-2B product is filtered with VDK8 
 
 The individual auxiliary data sets and models used during the post-processing steps mentioned above are provided as well (in the aux_data folder): 
 
 - 'GRAVIS-2B_2002095-2020091_GFZOP_0600_NFIL_0003.gz': Long-term mean field calculated as unweighted average of the 183 available GFZ RL06 GSM products in the period from 2002/04 up to and including 2020/03. 
 - 'GRAVIS-2B_COSTG_GRACE+SLR_LOW_DEGREES_0003.dat': time series of coefficients C20, C30, C21 and S21 estimated from a combination of GRACE/GRACE-FO and SLR 
 - 'GRAVIS-2B_GIA_ICE-6G_D_VM5a_0003.gz': Model from Peltier et al. (2018) for subtraction of linear trend caused by GIA 
 - 'GRAVIS-2B_COSTG_GEOCENTER_0003.dat': Time series with geocenter coefficients estimated from COST-G RL01 
 
 Further information about the Level-2B products and the auxiliary data is provided in the header of the corresponding data files. 
 
 Link to data products: ftp://isdcftp.gfz-potsdam.de/grace/GravIS/COST-G/Level-2B 
 
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 Version History: 
 
 21 April 2023: 
 Release of Version 0003. This is an update of Version 0002 of the same data set (see changelog). 
 
 15 June 2020: 
 Initial release of the data. Note that the initial version number is 0002 in order to reflect the consistent data processing of this data set and Version 0002 of the data set Dahle & Murböck (2019, https://doi.org/10.5880/GFZ.GRAVIS_06_L2B). 
 
 All changes and updates are documented in the changelog available via the data download section. Previously released versions of this data set are available at ftp://isdcftp.gfz-potsdam.de/grace/GravIS/COST-G/Level-2B/old_versions