Title: EUMETSAT and GRAS
1EUMETSAT and GRAS
C. Marquardt, A. von Engeln, Y. Andres, F.
Sancho Thanks to many, many more people
GSN/ESOC, GRAS SAF (DMI, MetO, ECMWF, IEEC), UCAR
2Content
- GRAS instrument
- Some operational aspects
- Raw sampling
- Structural uncertainty
- Infrastructure GRAS SAF, GSN
- Summary
3GRAS GNSS Receiver for Atmospheric Sounding
- Build by Saab Space (now RUAG, Sweden instrument
and antennas) and Austrian Aerospace (Austria
S/W, DSP) - Mass 30 kg, power 40 W
- 20 MB per orbit / 280 MB per day
- No heritage from the JPL series of RO receivers
(GPS/MET, CHAMP, GRACE, COSMIC, TerraSAR-X, ) - H/W S/W design AGGA2 until 1999 GRAS until
2003 (or so)
Launched 19th Oct 2006 switched on 27th Oct
2006 worked out of the box. Bending angles
operational 04/2008, ECMWF 05/08, MetO (N) 07/08
refractivity pre-operational 03/09
4Distribution of Data
- 650 occultations per day / single instrument
(sustained - dont use PRN 32 yet) - Requirement / expectation was 500 but we have
more GPS satellites than nominal - Metop is in a sun-synchronous orbit (930 am) by
design - always samples the same part of the diurnal cycle
5Statistics
- 4 weeks (30 Sep 2007 27 Oct 2007) 692 / 627
occs / day - Statistics collected from an early version of the
current GRAS prototype - Operational statistics similar (but without me
bugs-)
6Operational Aspects / Anomalies
- Buffer overflow on rare occasions (5 times since
launch) a threshold parameter needed to be
adapted via firmware patch - Single event of simultaneous tracking loss on the
zenith channels receiver recovered after a few
seconds (SAA) - GPS SV selection for onboard POD based on GPS
Almanachs instead of Ephemerides - occasional degradation of onboard navigation
solution - single event divergence of the onboard POD
required navigation solution reset from the
ground - GRAS is the instrument with the lowest number of
instrument anomalies on Metop (by far)
7Raw Sampling
- Operational GRAS processing currently based on
geometrical optics - Raw sampling (or open loop) data not yet
exploited - Currently prototyping reconstruction and
retrieval algorithms for tropospheric data in a
joint study with ESA / RUAG / DMI GRAS SAF /
University of GRAZ / GFZ (and DLR for orbits) - First retrievals to the ground done by DMI
- We expect results to become operational by the
end of the year - Demonstration data will be available earlier
- Reconstruction software will be available as OSS
8Raw Sampling (contd)
C/A
P1, P2
9Spectra / Radioholography (Rising)
10Structural Uncertainty
ECMWF bias
- 30 days before Sep 24, 2008
- Operational monitoring at ECMWF
- Similar results at GRAS SAF, UK MetOffice, Meteo
France - Altitude region where RO is considered to be most
accurate (and unbiased)
GRAS (EUM) CHAMP/GRACE (GFZ)
COSMIC (UCAR)
(figure courtesy Sean Healy, ECMWF, from
operational monitoring)
11Structural Uncertainty (contd)
- Processing COSMIC excess phases (UCAR offline
processing, downloaded 01/2009) with GRAS
prototype - identical parameter settings for both retrievals
(but POD differencing independent) - UCAR processed bending angles as reference
- 30 Sep 28 Oct 2007
- 37157 (53813) COSMIC profiles
- 18577 GRAS profiles
- Compared w/ colocated ECMWF co-located 12 hourly
forecasts - Geometrical processing only DONT look into the
troposphere
Robust statistics (Tukeys biweight) for
objective Q/C
12Structural Uncertainty (contd)
- Systematic biases between 20 and 30 km understood
by now (implementation of excess phase filter) - Updates in the UCAR processing will address this
in the near future - Biases above 30 km remain to be understood
- Yes, there is structural uncertainty in RO, but
- even significantly different GPS instruments
agree exceptionally well when being processed
consistently - Intercomparing independent processing results
will allow to quantify (and possibly resolve)
these issues - Effects are tiny a few 0.1 (corresponding to a
few tenth degrees)!
Robust statistics (Tukeys biweight) for
objective Q/C
13Upper level noise (bending angles)
- Same experiment
- upper level (60 80 km) noise estimates against
CIRA/MSIS - Used to demonstrate conformance with
requirements max. abs. error lt 1 µm,
one sigma 0.65 µm - COSMIC and CHAMP data processed with same
settings as GRAS data (in particular filter
settings) to get a comparable relative noise
estimate - Lower noise due to USO zero differencing
14Upper level noise (excess phase)
- Generalized Cross Validation for spline fitting
over first 20 seconds - RMS from fit as proxy for (thermal) noise and
differencing errors
15GRAS Meteorology Satellite Application Facility
- GRAS SAF is a joint effort between
- DMI - operational level2 processing (N, P, T, q,
climate products), advanced algorithms (CT, FSI) - MetO - Data Assimilation, ROPP (forward operators
for RO data assimilation, data thinners, format
converters) - ECMWF - Data Assimilation, Re-analyses
- IEEC Reflections, data quality
- http//www.grassaf.org
- for monitoring, data S/W, user services,
16GRAS SAF (contd)
- Refractivity product declared pre-operational
in March 2009 - Still some issues w/ refractivity biases above 30
35 km due to statistical optimisation - Improved refractivity and additional level 2
products (p, T, q) expected in June/July, based
on ROPP - Climate products (gridded data, monthly means
etc.) in preparation - There will also be an offline product of GRAS
data for use in climate applications (better
orbits, improved algorithms)
Comparison w/ ECMWF (breakthrough and
threshold)
17GRAS Ground Support Network (GSN)
- Provides auxiliary data for GRAS processing
- designed, developed and validated by the
Navigation Support Office at ESOC - global network of 40 on-ground GPS receiver
stations delivering data to a processing centre
located at ESOC through subcontractors (NRCan,
Fugro, GFZ, ESOC) - Data collected and processed at ESOC HQ in
Darmstadt - GPS orbits, clocks, EOPs, network data for
differencing (not used at present) in NRT
sufficient for NWP applications
Primary set of GSN ground station network
18GRAS GSN (contd)
- Evolution over the next months
- Port to state-of-the-art NAPEOS
- Identical software as used by ESOCs IGS
processing (but still differences due to
different input data etc.)
3D-RMS
19Summary
- GRAS has been performing excellently since
Metops launch - No major anomalies
- Only a single firmware update so far (and none
foreseen) to fix a parameter setting - So far, data quality continues to exceed
expectations / requirements - Starting to look into raw sampling data
- Excellent consistency between closed loop and raw
sampling data - current emphasis
- advanced algorithms taylored for GRAS data,
navigation bit removal - Joint study w/ RUAG, DMI/GRAS SAF, University of
Graz, and further collaborations with GFZ Potsdam
and UCAR/COSMIC ongoing - first data being analysed
20Summary (contd)
- Structural uncertainty
- 2009 Re-engineering of the operational GRAS
processing software to - extend GRAS data into the troposphere (raw
sampling) - improve orbit quality stability
- develop multi-mission capability
- reprocess existing data set with improved
algorithms - GSN data quality will improve
- Operational bitgrabber network being considered
- SAF Level 2 products will become available