News related to GRACE Gravity Data

This page is regularly updated and contains important news about GRACE data products as well as useful hints how to use the most recent GRACE RL02 Level-1B and RL05 Level-2 data. Additional information may also be taken from the monthly GRACE SDS newsletters.

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/’).

2016

December 2016:

  • No RL05 Level-2 products could be generated and delivered for October 2016 due to insufficient amount of Level-1B data.
  • No RL05 Level-2 products could be generated and delivered for September 2016 due to planned switch-offs of the GRACE-A and GRACE-B Microwave Assemblies (MWA) and Instrument Control Units (ICU) on September 3 in order to reduce the load on the batteries.
  • Note that the RL05 Level-2 products for August 2016 generated and delivered by CSR, GFZ and JPL are based on 27 days of data between August 8 and September 3. The quality of these fields is reduced above approximately degree and order 25 compared to previous monthly solutions. The reasons are still under investigation by the SD

June 2016:

  • No RL05 Level-2 products could be generated and delivered for April 2016 due to planned switch-offs of the GRACE-A and GRACE-B Microwave Assemblies (MWA) and Instrument Control Units (ICU) in order to reduce the load on the batteries.
  • Due to a processing bug, the originally published GFZ Level-2 GSM product for February 2016 (labelled ‘GSM-2_2016029-2016060_0032_EIGEN_G---_005a‘) turned out to be erroneous. A correct product has been generated which has replaced the previous wrong one in the GRACE archives ISDC and PO.DAAC. Please make sure that you use the correct version of the GSM product for February 2016. This can be checked by looking at the product generation date (to be found in the record ‘FIRST’ of the Level-2 product file) which should be ‘20160615’. Note that only the GSM files (*.gz and *.txt) are affected; the corresponding GAx products remain unchanged.

May 2016:

  • Note that the RL05 Level-2 products for February 2016 generated and delivered by CSR, GFZ and JPL are based on 32 days of data between January 29 and February 29.

March 2016:

  • Note that the RL05 Level-2 products for January 2016 generated and delivered by CSR, GFZ and JPL are based on 25 days of data between January 4  and January 28.

February 2016:

  • Note that the RL05 Level-2 products for December 2015 generated and delivered by CSR, GFZ and JPL are based on 24 days of data between December 11  and January 3.

January 2016:

  • No RL05 Level-2 products could be generated and delivered for November 2015 due to planned switch-offs of the GRACE-A and GRACE-B Microwave Assemblies (MWA) and Instrument Control Units (ICU) in order to reduce the load on the batteries.

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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