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in print
Dr. Alan Belward
Chair, WGCV,
European Commission DG-JRC
Since its inception in 1984 the Working Group on Calibration and Validation has focussed on ways in which the group can help ensure long term confidence in the accuracy and quality of Earth observation data and products from satellites. The topics debated by the Working Group centre on two key issues; firstly sensor-specific calibration and validation, and secondly geophysical parameter and derived product validation. WGCV provides a forum for calibration and validation information exchange, co-ordination and co-operative activities. The WGCV promotes the exchange of technical information and documentation, joint experiments, and the sharing of facilities, expertise and resources among its members as appropriate. This approach has served the community well over the last sixteen years, leading to better quality data, better documentation and sustained commitments to provide calibration updates. But more of the same is not enough.
Whilst debate and exchange of information are essential, WGCV is by
no means the only mechanism for this; scientific workshops and conferences
too
provide opportunities for public debate and peer review. But unlike
WGCV these always embrace a range of issues, rather than focussing, and
discussion
is always time limited. WGCV provides an opportunity to achieve far
more. The Working Group and its all-important technical sub-groups provide
a forum for sustained debate, international co-operation and common actions
too. In particular this last attribute is under exploited. WGCV membership
embraces all the world's major civil agencies responsible for Earth observation
satellite programmes and international user organisations. This is a powerful
combination and one with the potential to answer a key "cal/val" question...
who is responsible for and performing the cal and val?
As the Integrated Global Observing Strategy (IGOS) gains momentum there
will be an increased need to co-ordinate and steer the transition of scientific
output to operational observations. Central to the IGOS concept is
use of resources (be they in situ or space) from multiple providers. The
requirements from cal/val perspective are clearly common standards
and common methods. Issues such as traceability*1 and the need for shared
access to in situ observations arise from these requirements.
The civil space agencies accept the responsibility for instrument calibration
and invest a great deal of time, effort and financial resources in ensuring
long-
term instrument calibration. The costs in these terms of dealing with
traceability are at present largely unquantified. Through the conventional
WGCV route
of debate and discussion WGCV intends in 2000 to document the ramifications
of traceability for future mission planning.
A number of agencies (both CEOS Members and Associates) too are establishing
in-situ measurements at validation sites, airborne campaigns, and acquisition
of high-resolution satellite data as part of strategies for product validation.
There is an unequivocal need for proactive measures to ensure common validation
protocols. A common approach will allow widespread use of validation data,
and work towards standardised approaches to global validation. Guidance
is needed for in situ data collection, instrumentation, sampling designs
and strategies, modelling and dealing with transitions of scale from in
situ to airborne, and satellite data. The use of data from multiple sensors
operated by different agencies for creation of global products
means that the need to work together is stronger than ever.
At the end of 1999 WGCV created a new sub group to examine land surface parameter validation. This group must ensure global co-ordination of these efforts. It is probably too early in the process to advocate a more "hands-on" approach than has traditionally been the role of WGCV, but there is a real risk that without growth in this direction validation of global products (especially terrestrial products such as land cover) will remain elusive. WGCV is a recognised international forum with dedicated and committed members, in 2000 we expect that participation from both Member and Associate CEOS organisations will lead to significant steps forward in terms of validation of global products.
*1: Traceability refers to an auditable route describing and confirming
the calibration chain and attributed accuracy back to an internationally
agreed reference, usually SI as maintained by a national standards laboratory.