News related to GRACE Gravity Data

This page is regularly updated and contains important news about GRACE data products from the Science Data System (SDS) as well as useful hints how to use the most recent GRACE RL02/RL03 Level-1B and RL06 Level-2 data. Additional information may also be taken from the monthly GRACE SDS newsletters.

2018

November 2018:

  • The GRACE mission ended with last science data collected in June 2017, and the satellites re-entering in December 2017 and March 2018.
  • CSR, GFZ and JPL are in progress to reprocess the complete GRACE mission. The resulting RL06 Level-2 products are based on RL03 KBR1B and SCA1B instrument data, improved background models such as AOD1B RL06 and updated standards. RL06 will serve as the basis for extension of the GRACE time series with GRACE-FO data.
  • The following GRACE RL06 data products and related documentation are currently available:

    • Level-1B KBR1B and SCA1B RL03 data for the period April 2002 till August 2016
    • Level-2 GSM products in terms of spherical harmonic coefficients up to degree and order 60x60 and 96x96 for the periods

      • April 2002 till August 2016 (CSR)
      • April 2002 till August 2016 (JPL)
      • January 2003 till November 2014 (GFZ)

      (Note: missing products from all centers are coming soon! Please check the archives regularly.)

    • Corresponding Level-2 GAA, GAB, GAC and GAD products up to degree and order 180x180
    • CSR/GFZ/JPL RL06 Level-2 Release Notes
    • CSR/GFZ/JPL RL06 Level-2 Processing Standards Documents
    • An updated version of the Level-2 User Handbook describing the new Level-2 filenames and YAML headers

  • The SDS is looking forward to get user feedback on the data quality, changes, and any open questions related to the new GRACE RL06 data products.

2017

September 2017:

  • CSR, GFZ and JPL have generated and delivered RL05 Level-2 products for June 2017 based on 37 days of data between May 23 and June 28 (CSR) and 38 days of data between May 23 and June 29 (GFZ, JPL). The quality of these products is impacted by the facts that

    • No accelerometer data for GRACE-B are available for this month; therefore, the GRACE-A accelerometer data was used as a “transplant” to derive non-gravitational accelerations acting on GRACE-B (see also news from April 2017).
    • The change of the satellites’ pitch angles (see corresponding bullet below).

  • CSR, GFZ and JPL have generated and delivered RL05 Level-2 products for May 2017 based on 21 days of data between May 2 and May 22. As the GRACE-B accelerometer has been switched on again for the period May 2 till May 24, solely original ACC1B data for GRACE-B and no “transplant” ACC1B data from GRACE-A have been used to generate the May 2017 solutions. However, the quality of these products might be impacted by the fact that the satellites’ pitch angles were changed (see corresponding bullet below).
  • CSR, GFZ and JPL have generated and delivered RL05 Level-2 products for April 2017 based on 28 (CSR) and 29 (GFZ, JPL) days of data between April 10 and May 8. The quality of these products is impacted by the facts that

    • No accelerometer data for GRACE-B are available for this month; therefore, the GRACE-A accelerometer data was used as a “transplant” to derive non-gravitational accelerations acting on GRACE-B (see also news from April 2017).
    • The change of the satellites’ pitch angles (see corresponding bullet below).

  • CSR, GFZ and JPL have generated and delivered RL05 Level-2 products for March 2017 based on 29 days of data between March 17 and April 14. The quality of these products is impacted by the facts that

    • No accelerometer data for GRACE-B are available for this month; therefore, the GRACE-A accelerometer data was used as a “transplant” to derive non-gravitational accelerations acting on GRACE-B (see also news from April 2017).
    • The change of the satellites’ pitch angles (see corresponding bullet below).

  • On March 29, 2017, the pitch angles of both spacecraft were set to 0° in order to improve the quality of the transplanted GRACE-B ACC1B product. However, this also lead to higher noise in the KBR1B data and significantly larger K-band range-rate residuals were observed since then. Note that also the quality of the Level-2 products might be additionally degraded due to this fact.
  • No RL05 Level-2 products could be generated and delivered for February 2017 due to insufficient amount of Level-1B data.
  • GFZ has generated and delivered RL05 Level-2 products for January 2017 based on 27 days of data between January 7 and February 2. CSR and JPL have generated and delivered RL05 Level-2 products for January 2017 based on 28 days of data between January 7 and February 3. The quality of these products is impacted by the fact that no accelerometer data for GRACE-B are available for this month; therefore, the GRACE-A accelerometer data was used as a “transplant” to derive non-gravitational accelerations acting on GRACE-B (see also news from April 2017).

April 2017:

  • CSR, GFZ and JPL have generated and delivered RL05 Level-2 products for December 2017 based on 27 days of data between December 11 and January 6. The quality of these products is impacted by the fact that no accelerometer data for GRACE-B are available for this month (see bullets below).
  • CSR, GFZ and JPL have generated and delivered RL05 Level-2 products for November 2017. The CSR products are based on 28 days of data between November 13 and December 10, the GFZ products are based on 21 days of data between November 14 and December 9 (without November 21, November 22, November 23, November 24, and November 25) and the JPL products are based on 23 days of data from November 14 till December 10 (without November 30, December 1, December 2, and December 3). The quality of these products is impacted by the fact that no accelerometer data for GRACE-B are available for this month (see bullets below).
  • Level-2 products for the mission period after November 2016 are generated using synthetic GRACE-B ACC1B R3 data (see bullet below) and other routine mission data. We believe that users whose analysis domain is smaller than 750 km radius will see considerably more noise than they would have in the mid-mission data (up to 2010); and noticeably more noise than they would have through the years 2015 and 2016. At spatial scales longer than 750 km, the products since November 2016 are slightly degraded relative to the Level-2 products from earlier in 2016. The Level-3 mascon or gridded data products derived from the project Level-2 gravity field models may be more suited for use at smaller spatial scales.
  • Since October 2016, the GRACE-B accelerometer is powered off due to battery limitations within the spacecraft. However, all other science measurements are periodically available - starting from November 2016 - for both spacecraft, resulting in the need to synthesize GRACE-B accelerometer data to allow gravity recovery analysis during this period. Synthetic measurements for GRACE-B accelerometer have been created using the GRACE-A accelerometer measurements, after appropriately accounting for a variable separation between the two satellites, and the small differences in the orientation of the two spacecraft relative to each other. This synthetic ACC measurement is labeled GRACE-B ACC1B R3 dataset, and is delivered together with the other Level-1B datasets (at ISDC: subdirectory ‘Level-1B/JPL/INSTRUMENT/RLR3/’).

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Contact

Christoph Dahle
Section 1.2: Global Geomonitoring and Gravity Field

c/o DLR Oberpfaffenhofen
Münchner Str. 20
D-82234 Wessling

Tel.: +49 8153 90832 16
Mail: christoph.dahle(at)gfz-potsdam.de