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GRACE Data File Formats

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Tyler C Sutterley edited this page Oct 18, 2017 · 1 revision

Product Identifier

GRACE Level-2 products consist of spherical harmonic coefficients of the Earth's gravitational field. The data files are typically gzipped ascii files with names formatted as the following: PID-2_YYYYDOY-yyyydoy_ndays_center_flag_rrrr

  • PID is a product identification string (for standard products: GSM, GAD, GAC, GAA, GAB)

  • -2 denotes that the data is a GRACE Level-2 product

  • YYYYDOY denotes the start date (year and day-of-year) of the measurement range

  • yyyydoy denotes the end date (year and day-of-year) of the measurement range

  • ndays is the number of calendar days used to produce the monthly estimate

  • center is an institution specific string (UTCSR for CSR, JPLEM for JPL Spherical Harmonics, JPLMSC for JPL Mascons, EIGEN for GFZ)

  • flag is a 4 character processing center dependent string (CSR denotes the maximum degree and possibly maximum order of the solutions, JPL denotes if the data is an intermediate release, GFZ denotes constrained versus unconstrained solutions)

  • rrrr is a 4 character release string which is typically a 4 digit number (GFZ datasets can denote intermediate releases in the 4th character)

Character Description

1st Description
G Geopotential coefficients
2nd Description
S Estimate made from only GRACE data
C Combination estimate from GRACE and terrestrial gravity information
E Any background model specified as a time-series
A Average of any background model over a time period
3rd Description
M Estimate of the Static field 1
U Geopotential estimate relative to the background gravity model
T Total background gravity model except for background static model
A Non-tidal atmosphere 2
B Non-tidal Oceans 2
C Combination of non-tidal atmosphere and ocean 2
D Ocean bottom pressure product 3

[1]: Data files for this product also contain records with the epochs and rates used to model secular changes in the background gravity model.
[2]: see AOD1B Description Document.
[3]: Summation of non-tidal ocean and atmosphere over the ocean. Atmospheric pressure values are equal to zero over the land.

Summary

  • GSM: Geopotential coefficients of the static gravity field estimated from GRACE satellite data (produced by all centers).

  • GAA: Non-tidal atmosphere geopotential coefficients averaged over certain time period (produced by GFZ & JPL).

  • GAB: Non-tidal ocean geopotential coefficients averaged over certain time period (produced by GFZ & JPL).

  • GAC: Combination of non-tidal atmosphere and ocean averaged over certain time period (produced by all centers).

  • GAD: Ocean bottom pressure product. Combination of surface pressure and ocean pressure over the oceans, zero over the land (produced by all centers).

Reference

Srinivas Bettadpur, Gravity Recovery and Climate Experiment: Level-2 Gravity Field Product User Handbook, Technical Document GRACE 327-734, Revision 3.0, Center for Space Research, University of Texas, Austin (2012).

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