CSR Release-06 GRACE Level-2 Data Products
Updated: 2018-04-26
Thank you for your interest in the latest, Release-06 GRACE Level-2 data products. Users looking for our mean (static) Earth gravity field model may visit the GGM05 web page (http://www2.csr.utexas.edu/grace/gravity/); or visit the ICGEM website (http://icgem.gfz-potsdam.de/home) for our latest model GGM05C, as well as a variety of other mean field models.
This page describes the RL06 time-series of monthly time-variable gravity field estimates. The description on this page is presently intended for users already familiar with the nomenclature and use of GRACE Level-2 data products.
As of today (Apr 26, 2018) the CSR RL06 Level-2 data products are available for the span Jan 2003 through Aug 2016. The RL06 products for the 2002 months will be delivered as they are produced within the next few weeks. The RL06 data products for month with single accelerometer data will be produced and released over the next month. The RL06 data products include new GSM, GAC and GAD data products.
Further Details on RL06 Re-processing
What do we mean by re-processing?
With this transition, we have replaced both the Level-1B and the Level-2 data products.
| Data | Old | New |
|---|---|---|
| Level-1B | Version 2 | Version 2 and Version 3 |
| Level-2 | RL05 | RL06 |
The version number of the products can be identified by the data file headers and in the filename. Please see the Product Specification Document and other SDS documents for further details.
The improvements in the new products include improved parameters, processing algorithms, data editing and background gravity models.
The information content of the RL06 GSM files is the same as that of RL05 GSM files, in the sense that both the GSM time-series represent the same mass re-distribution processes: e.g. due to hydrology, cryospheric processes, and variations relative to the background models for the oceans and atmosphere.
More details on the re-processing will be provided shortly.
Data Access
As before, users may access all GRACE data products and documents through PO.DAAC (ftp://podaac.jpl.nasa.gov/allData/grace/L2/CSR/RL06/) or through ISDC (http://isdc.gfz-potsdam.de/grace).
Information Content in RL06 GSM Files
The information content in RL06 GSM files is the same as in the previous (RL05) GSM files. That is, the RL06 GSM files continue to represent the total gravity variability due to land surface hydrology, cryospheric changes, episodic (earthquake) processes, glacial isostatic adjustment (GIA), and corrections to the background models for atmospheric and oceanic processes. The RL06 GSM products can continue to be used in the same way as RL05 GSM products.
Changes to the GSM Filename
The definition of certain fields in the Level-2 filenames have changed in order to comply with GRACE-FO filename conventions. Please refer to the Level-2 handbook for more details (ftp://podaac-ftp.jpl.nasa.gov/allData/grace/docs/L2-UserHandbook_v3.0.pdf).
A GRACE Level-2 gravity field product is a set of spherical harmonic coefficients of the exterior geopotential. A product name is specified as
PID-2_YYYYDOY-YYYYDOY_dddd_sssss_mmmm_rrvv
| Field | Meaning |
|---|---|
| PID | 3-character product identification mnemonic |
| -2 | Denotes a GRACE Level-2 product |
| YYYYDOY-YYYYDOY | Specifies the date range (in year and day-of-year format) of the data used in creating this product |
| dddd | Specifies the gravity mission |
| sssss | Institution specific string |
| mmmm | 4-character mnemonic used to identify the characteristics of the gravity solution |
| rrvv | 2-digit (leading-zero-padded) release number and 2-digit (leading zero-padded) version number |
Product Identifier Mnemonic
The Product Identifier mnemonic (PID) is made up of one of the following values for each of its 3 characters:
| Position | Code | Meaning |
|---|---|---|
| 1st Character | G | Geopotential coefficients |
| 2nd Character | S | Estimate made from only GRACE data |
| C | Combination estimate from GRACE and terrestrial gravity information | |
| A | Average of any background model over a time period | |
| 3rd Character | M | Estimate of the Static field |
| U | Geopotential estimate relative to the background gravity model | |
| A | Non-tidal atmosphere (see AOD1B Description Doc) | |
| B | Non-tidal Oceans (see AOD1B Description Doc) | |
| C | Combination of non-tidal atmosphere and ocean - for details of combination see AOD1B Description Doc | |
| D | Bottom-pressure over oceans, zero over land – for details of combination, see AOD1B Description Doc |
Gravity Mission Codes
The ‘dddd’ string specifies the gravity mission:
| Code | Mission |
|---|---|
| GRAC | Gravity Recovery and Climate Experiment |
Institution Codes
The ‘sssss’ string specifies the institute where the data were processed:
| Code | Institute |
|---|---|
| UTCSR | The University of Texas at Austin Center for Space Research |
| JPLEM | NASA Jet Propulsion Laboratory |
| GFZOP | GFZ German Research Center for Geosciences |
Gravity Solution Characteristics
The ‘mmmm’ string is a 4-character mnemonic used to characterize the gravity solution. The first character is used to identify the primary observation type used in the gravity solution (Note: MWI = Microwave Instrument). The second character defines the size of the spherical harmonic expansion in the file. The third and fourth characters are used to represent other characteristics of the gravity solution, including the type of basis function used, whether it is an unconstrained or constrained solution, and the type of windowing function used. For any files that describe the average of a background model (where ‘A’ is the 2nd character in the PID), only the 2nd character in the ‘mmmm’ string is defined/applicable. The 1st, 3rd, and 4th characters are set to be equivalent to the corresponding gravity solution.
| Position | Code | Meaning |
|---|---|---|
| 1st Character | A | MWI range data |
| B | MWI range-rate data | |
| C | MWI range-acceleration data | |
| 2nd Character | A | 60 x 60 spherical harmonic expansion |
| B | 96 x 96 spherical harmonic expansion | |
| C | 180 x 180 spherical harmonic expansion | |
| D | 60 x 30 spherical harmonic expansion | |
| 3rd and 4th Characters | 01 | Unconstrained spherical harmonic solution with a boxcar windowing function |
The ‘rrvv’ string indicates the release (rr) and version (vv) of the solution. The release number is tied to a specific set of background force models, and indicates consistency between solutions across different missions. All quicklook solutions will be given a release number of ‘QL’. The version number indicates the version of the solution under a specific release.
Replacement SLR-derived C20 Values
The RL06-compatible values of SLR-derived C20 harmonics are provided in the new Technical Note 11 (TN11).
GRACE-SDS recommends that users should replace the C20 values within the CSR/GFZ/JPL-RL06 GSM files with the corresponding values from TN11.
The TN11 values of SLR-derived C20 are not inter-changeable with the TN07 or TN05 values, due to changes in background models, and due to an absence of background rates modeled in the former.
Some Relevant Publications
- Save, H. and the CSR Level-2 Team, “GRACE RL06 Reprocessing and Results from CSR,” EGU2018-10697, EGU General Assembly 2012 [pdf 9MB]
Ancillary Data Products
For the replacement SLR-derived C20 values, see the section above.
Additional regularized RL06 GSM product time-series and RL06 mascon solutions should be available shortly.
Please revisit these pages for further information.