GERB status

1
GERB status

• J E Russell

2
GERB data

• Nominal GERB region 60N-60S, 60E-60W
• Scanned in shortwave (0.3 to 4?m) and total bands
  (0.3 to gt200?m) in just over 51/2 minutes
• Flux products for region provided as 3 scan
  averages (1642), or 15 minute averages.
• GERB-2 on geostationary MSG-1 began commissioning
  beginning 2003 at 10?W. Satellite declared
  operational Feb 2004, moved to 3.5?W. First
  release of GERB data last month
• GERB-1 launched on MSG-2 Dec 2006 and currently
  being commissioned

Total channel
Longwave
Shortwave channel
3
15 minute GERB fluxes
LW
SW
1200 14/04/06
4
GERB MSG-1

• GERB on MSG has been operating for 3.5 y
• This is nominal design lifetime, but satisfactory
  science data is still being acquired. Since Feb
  2005 occasional mirror mis-pointing events occur,
  periods where these are more frequent and less
  frequent are apparent but no trend is
  identifiable since Feb 2005
• Current plans will keep MSG-1 GERB as the
  operational instrument for the moment, probably
  until after the equinox and possibly until the
  end of the year (decision depends on EUMETSAT and
  SEVIRI)

5
GERB MSG-2

• Turned on Jan 2006
• After a few days of pre-eclipse calibration tests
  GERB on MSG-2 was place in SAFE (non-rotating)
  mode for the first spring eclipse period,
  calibration commissioning operations resumed at
  the end April
• All commissioning operations are complete
• MSG-2 will be relocated at 0 deg from 5th-17th
  July
• Overlap operations are planned for August and
  possibly longer but given that GERB-3 wont be
  operational before 2012 there is pressure to
  conserve GERB-1 operating lifetime

6
Eclipse ops

• A new software patch which offers improved (not
  100) safety benefits during eclipse operations
  has been installed and tested on both GERBs
• MSG-1 GERB operated through the spring 2006
  eclipse without incident (although the new patch
  did operate to safely place the instrument in an
  AUTO-SUNBLOCK configuration on several
  occasions in response to mirror pointing
  irregularities
• A decision on which GERB instrument to operate
  during the Autumn 2006 eclipse period is pending

7
GERB data

• GERB level 2 (V003) ARG products were released as
  Edition 1 data from the ggsps at end May of this
  year
• NANRG and BARG products should follow shortly
• Current Edition record runs from 25 March 2006 to
  present less 40 days
• Reprocessing of old data will begin when
  reprocessing machine is set up
• Priority periods (March 2006, June-July 2004
  Dec 2004-Jan 2005, Feb 2004 have been
  identified), however a full reprocessing starting
  Feb 2004 may be more feasible (TBD), may take 3
  months / year

8
Geolocation
Target accuracy 0.1 GERB pixel Requires precise
knowledge of where in the MSG spin (100rpm) data
is acquired.
Accuracy of spin timing information from MSG much
poorer than specified, plus delay in obtaining
spin structure axis misalignment information from
EUMETSAT interim solution is to match GERB to
SEVIRI observations.
Performance most pixels matched to 0.5 pixel
90 to 0.33 pixel 75 matched to 0.25 pixel.
Stability of optical model derived from retrieved
geolocation
1 of cases
4 of cases
5 of cases
15 of cases
25 of cases
10 of cases
20 of cases
20 of cases
Long term develop hybrid analytical/empirical
model for motion of spacecraft and satellite
rotation. Not all aspects of geolocation
behaviour currently understood
9
Inter-comparison of GERB and CERES radiances
Valuable collaboration between GERB and CERES,
and thanks to CERES team for helping GERB
project Special scanning pattern enables CERES
to view same surface pixel along same line of
sight Particularly important for highly
anisotropic SW radiances
Best fitGERB1.02xCERES3.5Wm-2sr-1
Best fitGERB1.004xCERES-1.8Wm-2sr-1
SW
LW
ltGERBgt/ltCERESgt1.05ltGERBgt-ltCERESgt5Wm-2sr-1
ltGERBgt/ltCERESgt0.99ltGERBgt-ltCERESgt-0.8Wm-2sr-1
10
GERB data accuracy
11
GERB data intercomparison

12
Radiance comparison scene dependency
13
LW Flux comparison
GERB ARG/CERES FM2June 2004
Semi-transparentcloud
Limb darkening differences
Night
Day
LW FLUX ratio
Know problems exist with the LW anisotropy
factors for semitransparent cloudDifferences
seen in the limb darkening of the CERES and GERB
fluxes Average GERB/CERES SW flux ratio 0.99
14
SW Flux comparison
Aerosol / cloud detection effects
GERB ARG/CERES FM2June 2004
Cloud detection and disk edge (resolution) effects
VZA 70? limit
Clear sky
All sky
SW FLUX ratio
Anisotropy factors are found to be 1 higher than
CERES for same scene Average GERB/CERES SW flux
ratio 1.07
15
Processing improvements in the pipeline

• Geolocation method (by matching) not ideal
  solution and cant meet spec for some products
  improvement and further information on spacecraft
  behaviour still required
• Spectral response Ongoing analysis of the
  GERB-CERES differences, including further
  measurements on flight spare detector to provide
  further input to detector spectral response and
  pixel-to-pixel variability
• LW and SW radiance to flux conversion Improving
  accuracy of fluxes is an ongoing research
  activity, specialised treatment of SW fluxes in
  the presence of aerosol and LW fluxes for thin
  cloud being developed. Clear sky diurnal
  asymmetry problem being improved.