1 GRACE Science Team Meeting Potsdam October 2007 GRACE Science Data System Status Michael Watkins, Gerard Kruizinga, Da Kuang, Willy Bertiger, Dah-Ning Yuan Jet Propulsion Laboratory, California Institute of Technology Frank Flechtner, Roland Schmidt, Uli Meyer, Christoph Dahle GeoForschungsZentrum Potsdam Srinivas Bettadpur, Furun Wang Center for Space Research, University of Texas at Austin

2 GRACE Science Team Meeting Potsdam October 2007 Overview Level-0/Level-1 processing and alignments status Onboard detection of KBR Missed Interrupts Advisory for ACC1B data affected by “Disconnect Supplementary Heater Lines” (DSHL) events AOD status Level-2 Status and Product Availability Usage Notes

3 GRACE Science Team Meeting Potsdam October 2007 Level-0/Level-1 Processing Status Standard automatic Level-0/Level-1 processing is fully operational at PO.DAAC (JPL) since –Occasional manual interventions during off-nominal operations of the GRACE spacecraft. –Latency ~12 days to L-2 processing centers Quick look Level-0/Level-1 processing is fully operational at JPL since to monitor for non-nominal states of the science payload (latency ~24 hours)

4 GRACE Science Team Meeting Potsdam October 2007 Data Flow Statistics as of 27 September 2007 > 99.9 % of raw data has been retrieved successfully and reformatted by the Science Data System (data latency < 1.0 hour) 2005 days of Level-1B data have been distributed to the level-2 centers (CSR, GFZ,JPL) ( data latency < 12 days) –1952 days pass KBR quality check, which serves as proxy for overall data quality (24 days in 2007 affected by DSHL included) –1845 days all instruments available, required for nominal level- 2 processing

5 GRACE Science Team Meeting Potsdam October 2007 GRACE Alignment Status Eight simultaneous COM calibration maneuvers performed since July 2004 –Center of Mass for both GRACE S/C are located within the required 100 microns of the ACC proof mass COM. –COM calibration analysis continues to be limited by ACC “twangs” except last COM calibration maneuver (31 May 2007) –Trim performed 12 April 2007 (x,y,z components) Work on improving SCA alignment with respect to ACC is suspended

6 GRACE Science Team Meeting Potsdam October 2007 Center of Mass X-Alignment; Calibration & Tracking GRACE-AGRACE-B Trim

7 GRACE Science Team Meeting Potsdam October 2007 Center of Mass Y-Alignment; Calibration & Tracking GRACE-AGRACE-B Trim

8 GRACE Science Team Meeting Potsdam October 2007 Center of Mass Z-Alignment; Calibration & Tracking GRACE-AGRACE-B Trim

9 GRACE Science Team Meeting Potsdam October 2007 Onboard Detection of KBR Missed Interrupts (MI) Ground detection uses Level-1 software/algorithms to detect MI after data dumps. GSOC is automatically notified when a MI has occurred. Upon notification GSOC sends restart tracker to spacecraft at next commanding opportunity (Latency up to 24 hours) Onboard detection uses Level-1 software/algorithms to detect MI within 10 seconds of occurrence. Restart tracker command sent by onboard IPU autonomously upon detection –Expected MI detection rate 95 % –Ground detection still needed for 5 % –Very few false positives expected (e.g. Solar Activity) –KBR data loss minimal (< 40 seconds) –Significant risk reduction of data corruption due to anomalous MIs

10 GRACE Science Team Meeting Potsdam October 2007 GRACE-A/B Accelerometer Y-axis bias (SRF) Time History after DSHL (GR-B) Event of 23-July-2007 DSHL (Jul ) Reheating Step 1 only (out of 4) Continue reheating Table-B activated (Aug )

11 GRACE Science Team Meeting Potsdam October 2007 New Thermal Regime Since Aug 2007 Power management concerns have led us to lower the heater set-points at select locations on satellites in order to conserve power.

12 GRACE Science Team Meeting Potsdam October 2007 ACC1B Data Advisory affected by DSHL events ACC biases (all three axis) show exponential decay signature after a DSHL event (4-5 days before stabilization occurs) Nominal Level-2 processing is not possible during these intervals Modeling of ACC biases as a function of time during these events may be possible but requires an in depth study of it’s effect on the gravity field solutions which is beyond the scope of the L1 processing. No ACC bias model is applied in the ACC1B data ACC1B data affect by DSHL events are identified in SDS news letter

13 Atmosphere and Ocean De-aliasing Level 1B (AOD1B) Release 04 (RL04) based on ECMWF 6h meteorological data and output from (mass conserving) baroclinic ocean model OMCT routinely generated at GFZ. Available since January 1, 2001 until today. RL01 and RL03 generation stopped with June 30, 2007 and January 31, 2007 products, respectively (formerly used in CSR RL01 and GFZ RL03 GSMs). AOD1B RL04 has been extended backwards to 1991 (back to 1976 planned) based on ERA40 (ECMWF Re-Analysis) data for improved Lageos data processing (see talk by König et al., Session B, Tuesday). Dealiasing Product Status

14 S22 and (to a smaller extent) C22 AOD1B RL04 “ocn” (OMCT output) and “oba” (ocean bottom pressure = “ocn” + surface pressure) coefficients show an inconsistency in June 2006 which is not visible in the “atm” S22/C22 coefficients (vertical integration also using surface pressure). Other AOD1B RL04 coefficients do not show this behaviour! No changes at ECMWF, no changes in the AOD1B/OMCT software. Reason under investigation: S2 tide reduction in OMCT surface pressure? S22 minus daily mean OCN ATM OBA June 2006 AODBRL04 C22/S22 Potential Issue

15 CSR, GFZ, and JPL have all developed new Release 4 (RL04) solutions in Fall 2006 (first discussed at last year’s GSTM) Centers have extended and improved these series from (minus few degraded months - typically months total) These solutions are significantly better than past generation solutions Improved background static field, tides, etc Generally consistent models and quality but Pay attention to differences in individual models and standards JPL and several other organizations (GSFC, OSU…) also produce alternative basis function (non spherical harmonics) solutions Mascons, grids, wavelets, etc, etc General Level-2 (gravity fields) Product Status

16 CSR RL04: From April 2002 through June 2007 –Except: May-June 2002 and June 2003 –Solved and delivered to degree/order 60 No constraints applied Starting with Sep 2007 solution, CSR RL04 solutions will use ITRF2005. –Earlier solutions used ITRF2000 –Changes: Station coordinates, velocities, and EOPDAT EOPDAT changes are an effective change in the background gravity model, as it changes modeled (2,1) harmonics through pole tide. Tests for past two months (May & June 2007) show no sensible difference between using ITRF2000 and ITRF2005. Long running standard series CSRRL01 is now terminated RL04 Products Delivered: –GSM-2: Monthly gravity field estimate –GAC-2/GAD-2: Average of the non-tidal atmosphere+ocean dealiasing model –Calibrated (provisional) error estimates (sigma-only) –Additional Info: SLR-based estimates of C20 (TN-05) CSR Level-2 (gravity fields) Product Status

17 GFZ Level-2 Product Status Monthly RL04 Level-2 products (EIGEN-GRACE05S) routinely generated based on improved background models and processing standards (nearly identical within SDS), Background gravity model EIGEN-GL04C (n=150) Drift rates for C21, S21, C20, C30 and C40 in background gravity field; epoch now (instead of ) Updated K2 (FES2002 values, see Lyard et al., 2006 (difference w.r.t CSR)) and included M4 tide in FES2004 ocean tides AOD1B RL04 de-aliasing IERS 2003 nutation and precession model JPL provided GPS antenna masks for GRACE-A/B For details see “GFZ L2 Processing Standards Doc. for RL04”

18 Evolution of Mean Field Quality (EIGEN example)

19 GRACE Science Team Meeting Potsdam October 2007 JPL GRACE Gravity Validation Solution Spherical Harmonic solution series JPLRL04 - Uses standards similar to CSR/GFZ but deliberately different processing algorithms - available from now replaced with JPLRL only change is improved GPS pseudorange/carrier relative weighting, only minor changes in gravity field - JPLRL04.1 extends from 2002-August 2007 (minus usual bad months) Mascon solutions JPLRL04.1M - Global 4 degree mascons from L1B range rate Research solution JPLRL04.1MRA - Global 4 degree mascons from handfiltered range acceleration

20 GRACE Science Team Meeting Potsdam October 2007 JPLRL04.1MRA Mascon solution (no destriping)

21 GRACE Science Team Meeting Potsdam October 2007 JPLRL04.1MRA (Greenland example) Details in Watkins et al. ”Alternate Gravity Field Represenations: Solutions Characteristics, and Issues” (Session A)

22 GFZ L2 RL04 Weekly Solutions Generated pure weekly subset solutions (n=30, 700km) and pseudo-weekly solutions (n=60) in terms of a moving average from weekly normals. Allows for an increased temporal resolution of gravity changes. Performance of weekly solutions clearly depends on data gaps and limited ground track coverage. Pure weekly subset solutions in general follow monthly solutions. Some of the outliers refer to weak solutions due to limited sampling /data coverage. Details by Dahle et al. ”Global GRACE-only gravity models with a weekly temporal resolution at GFZ Potsdam” (Session A) Higher Temporal Resolution: GFZRL04 Weekly Solution

23 Evidence of S2 aliased signal (top). –Several efforts underway for improving ocean tide models based on GRACE data. Chambers (bottom) reports potential evidence of K2 alias as well (1400 day period). –Can influence interpretation of inter-annual and secular change from GRACE.) GRGS, COS 161d, w/o C20 GFZ, COS 161d, w/o C20 [cm water] Tidal Aliasing and Mismodeling

24 GRACE Science Team Meeting Potsdam October 2007 Overall GRACE SDS Status Summary GRACE L1B data flowing well in automated system AODRL04 has become primary dealiasing product L2 Gravity Field releases RL04 from CSR, GFZ, and JPL all continue and improve –Some center-center differences that users should note Alternate solutions becoming more common and useful –offer potentially improved solutions in ranges of spatial wavelengths –full statistical characterization typically not available or well understood Users should definitely take a look at multiple solutions and compare SDS is always interested to hear from users about issues