1. GIST
AND INTERACTIONS WITH USERS
The 20th GIST meeting was held at the Environmental Systems Science Centre,
at Reading University, hosted by Prof A. Slingo, on 25-27th October 2003. This
reviewed ongoing project activities and provided a greater opportunity to view
the work of the ESSC in using GERB data. The first attendance of a representative
of the Edinburgh group demonstrated the widening interest in GERB data.
Further details on the performance of the GERB-2 instrument on MSG-1 appear
below. The minutes of the GIST meetings are available on request from the P.I.
The 21st GIST meeting will be held at the National Center for Atmospheric Research,
Boulder, Colorado, USA from 31 March to 2 April. The meeting will be held jointly
with the CERES Science Team meeting, illustrating the strong synergy between
the two experiments and teams. There are already several joint projects, notably
in the areas of directional models and in validation. Further projects are anticipated.
2.
GERB-1 INSTRUMENT
GERB-1 arrived back at RAL in July 2003. It was subsequently sent to Imperial
College for re-calibration and was returned to RAL towards the end of August
of the same year. A daughter board was designed to replace the battery, the
design of which was agreed with ESA, Alcatel and EUMETSAT. In this design, the
new emergency power source is the Nominal Survival heater supply, which is switched
either to the instrument or to the heater. The daughter board is required to
accommodate a 24V voltage regulator on an existing PCB within the IEU, to minimise
the amount of rework required within an already qualified unit.
The board was built, installed and tested successfully. A blanking plate was
made up to compensate for the mass lost due to the removal of the arming plug.
The unit was then resealed and underwent vibration and thermal vacuum testing
at the start of March 2004. It should be returned to Alcatel before the 25th
March 2004.
3. GERB-2
INSTRUMENT
GERB-2 remained in the ‘sunblock’ mode of operation from 1438 UTC on 15th August
to 1610 UTC on 3rd November for the autumn ‘sun avoidance’ season. Earth view
data are not collected in this mode. GERB Earth-viewing operation resumed with
‘deep space’ scans, to gain more information on the increased stray light seen
near the solstices, and the next in the series of calibration monitor observations
set up to track instrument shortwave gain. Following these, GERB has operated
in ‘normal’ mode collecting Earth-view data. As a conclusion to the programme
of calibration observations, an ‘Instrument Calibration Test Review Board’ was
held by telephone with EUMETSAT on 28th October. This agreed that the programme
had been completed successfully, but that further analysis activities remained.
These are, mostly, being carried out by Imperial College and the results are
feeding into the calibration parameters used in the GERB data processing.
MSG-1 was manoeuvred to its ‘nominal’ longitude of 3.5ºW during January
14th-27th and on mid-day 29th January went operational as Meteosat-8. The GERB
instrument continued to operate in ‘normal’ mode throughout the manoeuvre period.
The spring ‘sun avoidance’ season began on 14th February with GERB-2 now being
operated in ‘normal’ mode from 0156 to 2033 each day. During the remaining time,
operation is in ‘sunblock’ mode to prevent damage to the GERB-2 detectors by
their possible exposure to direct sunlight near midnight. EUMETSAT have accepted
this change as a result of improvements made to both the GERB-2 and Meteosat-8
on-board safeing software.
GERB-2 Commissioning & Operations were discussed with EUMETSAT and Imperial
College at a meeting on 25th-26th February at RAL. This reviewed the GERB ‘Flight
Operations Manual’, in the light of GERB-2 commissioning experience and the
ongoing ‘emergency power’ modifications that have been made to the GERB-1 and
3 instruments, and the ‘Operations Interface Control Document’ which defines
the details of the EUMETSAT-RAL and EUMETSAT-Imperial College operational interfaces.
These interfaces are working well and should ensure the continuing reliable
operation of the GERB-2 instrument.
4. GERB-3
INSTRUMENT
The instrument was delivered to Alcatel in June and a delivery review board
was held. The instrument was integrated onto MSG-3. The unit will be returned
for battery modifications in May 2004.
5. GERB–4
ACTIVITES
The goldblack deposition facility has been installed and commissioned at Leicester
University for the detectors. This work began in February 2003. The deposition
facility is fully operational and goldblack coatings have been produced since
October 2003. Characterisation of these coatings is now underway with effort
being concentrated on understanding the complex relationship between evaporation
rate, chamber pressure, substrate temperature, quantity of gold and deposition
rate and the spectral response. Good results have been obtained with the best
spectral performance showing less than 5% reflectivity out to ~25 micron.
So far, all blacking work has been performed on large area (2 cm x 2 cm) samples. The final detector deposition will require the use of a reticulated mask, so that only the detector pixels are coated (50 x 50 micron). A clamping facility has been designed and built to hold the detector and mask in sub-micron alignment during the coating process. The process has been optimised for deposition on a silica substrate and tests are being started on reticulated deposition. The actual blackening of the detector die is timetabled for the end of May 2004.
The other industrial partners were Kicked-off at the start of 2004. The various subsystems are due for delivery at RAL in December 2004.
6. GERB
GROUND SEGMENT AND OPERATIONS
6.1 Status of the GERB Ground Segment Processing
System (GGSPS)
The GERB Ground Segment Processing System (GGSPS) has continued to function
well. A spate of data-line problems before Christmas 2003 appear to have been
solved by BT and an ongoing, relatively minor, problem with the commercial data-base
system used by the GGSPS also appears to have been corrected by the suppliers.
The geo-location problems caused by systematic errors in the on-board ‘start
of line (SOL)’ signal have become better understood. In particular, it has been
found possible to make a correction based on ‘corrected start of line (CSOL)’
information routinely generated by EUMETSAT in the SEVIRI processing. A system
to transfer these CSOL data from EUMETSAT to RAL is now in place and has been
in operation for a few weeks (as of March 10th). The changes needed to the GGSPS
system for using these data have been designed, are being coded and are expected
to be in operation by the end of March. More detailed analysis of a sample of
CSOL corrected data is showing the need for second order geo corrections. These
arise because of the changes in instrument geometry caused by operation in the
16g environment of the spinning Meteosta-8 (these were predicted and estimated
pre-launch but operation in-orbit is allowing their refinement). In the longer
term, EUMETSAT have agreed to add the CSOL information to the GERB telemetry
stream rather than transfer these data as separate files. This will simplify
and make more reliable their association in the GGSPS.
With the routine dissemination of SEVIRI data by EUMETSAT, the system to obtain
SEVIRI header data, via the Royal Meteorological Institute of Belgium (RMIB),
is now in use. The ‘temporary’ system, implemented between EUMETSAT and RAL
to supply data files via an ftp server, has been retired but is anticipated
to be revived for MSG-2 commissioning.
6.2 Status of the GERB RMIB Processing System
The RMIB continues to generate GERB-2 data products. Their scientific value
has been increased considerably with the inclusion of a temporary, empirical
geo-location correction based on comparison of GERB-2 and SEVIRI data.