image
in print
Dr. Alan Belward, WGCV Chair, European Commission
The 15th meeting of the CEOS Working Group on Calibration and Validation
(WGCV) was held 14th to 16th April 1999, at the Andφa
Rocket Range kindly hosted by the Norwegian Space Centre. Discussion
on the roles and work of the WGCV were led by the keynote address from
Dr. Tillmann Mohr, Chair of CEOS who provided directions to Working Group
and a detailed update on the IGOS initiative. Dr. Mohr emphasised the need
for continued effort on calibration, the need for greater efforts concerning
product validation, and stressed the importance of validation to IGOS.
The need for product validation in the IGOS context was a recurrent
theme throughout WGCV15. The role of the National Standards laboratories
was considered particularly pertinent. Representative laboratories (notably
the USA's NIST and the UK's NPL) have been regular contributors to the
WGCV over the last three years. These laboratories have no formal representation
in CEOS but are making
valuable contributions to our thinking. In particular they have raised
the issue of "Traceability". Key points to emerge included a need for agencies
to demonstrate and confirm accuracy for instruments through independent
audit, and that all operating agencies ensure SI
measurements are traceable to international standards. Some agencies
involve National Standard Laboratories, and the feeling was that those
agencies with experience should share that experience with those who do
not. Traceability and error budgets are needed for every sensor. In the
context of IGOS the end-users need to have confidence in the data at the
instrument level (e.g. spectral radiance), and
this can be achieved by accountability through independent assessment.
It is also important that the quality of data products is traceable to
SI standards. The implications are far-reaching and WGCV will convene a
special ad-hoc group, with a life of 1 year, to look in depth at the issue
of traceability and its long-term consequences.
A special session on Norwegian Space Activities described the work of
the Norwegian Space Centre, the Nansen Centre, the Andφa Rocket Range,
the ALOMAR Facility, and Norway's work on SAR Wind Cal/Val for ENVISAT.
The proximity to the ALOMAR facility was a
catalyst for a special session on Atmospheric Chemistry led by Dr Evert
Attema of ESA concerning the lessons learned from GOME and the plans for
ENVISAT. There is international co-operation in atmospheric chemistry at
present (e.g. stimulated through agency programmes) but it could be improved
by the action of WGCV. Future action will centre on identifying atmospheric
chemistry points of contact and determining the degrees of international
collaboration deemed necessary and lacking. A model for future consideration
could be that of the IOCCG.
Dr Mohr's directions to WGCV added further impetus to a combined WGCV
/ ISPRS WGII/4, WGIII/6 workshop planned for May 26th-28th on Production
and Validation of DEMs and Terrain Parameters from Spaceborne Sensors.
The meeting, held at University College London examined issues including
existing validation activities, the role of terrain models in validation
of land surface related parameters, gaps in collaborative activities related
to calibration and validation for land surface related
parameters, validation protocols for land surface related parameters
and the role for WGCV.
The workshop identified a trend towards producing higher level products,
and that it is harder to validate these than it is to generate them, especially
as the costs of obtaining field data for validation are high, particularly
in proportion to the non-satellite budget of the observing
systems. The workshop concluded that co-ordinated international validation
initiatives would be beneficial to multiple space agencies, maximizing
limited resources for land product validation. A recommendation was made
to the WGCV to convene a new sub-group to examine Land Surface Parameter
Validation, and a mandate for such a group was drafted. Following the meeting
Dr. Jeffrey
Privette, EOS MODIS Land Validation Program, NASA/Goddard Space Flight
Center and Dr. Stefan Dech, German Aerospace Center (DLR) German Remote
Sensing Data Center (DFD) Oberpfaffenhofen agreed to co chair a new WGCV
sub group with the following objectives:
Full minutes of both meetings can be found on the WGCV web site http://wgcv.ceos.org/.
Thanks go to all individuals who participated in the two meetings and to
the CEOS members and associates who supported them.