SENTINELS
From INVESaTWIKI
SENTINELS
The ENVISAT satellite is the flagship of the fleet
of ESA earth observation satellites, targeted to operational
and sustainable services. Starting with the
C-Band SAR observations with ERS-1 in 1991, followed
by ERS-2 in 1995, ESA launched ENVISAT
in 2002. It delivers, multi-functional C-Band SAR
(ASAR), medium resolution superspectral optical data
(MERIS) and other information, such as by a suite
of atmospheric sounders. However, already during the
construction of ENVISAT, it became clear to ESA and
its member states that putting all these sensors on one
single and expensive satellite could not be a way to
operate in the future. But up to 2003, no real follow-on
satellite was envisaged to continue the service under
the ESA logo.
The go ahead for the GMES implementation plan by
the European Commission and ESA, backed by the requirements
analysis of primarily the ESA GMES Service
Elements, changed this situation. By early 2004
ESA suggested to define, launch and operate a fleet of
satellites, specifically addressing the European GMES
needs. These “Sentinels” are currently under discussion
and comprise:
- Sentinel 1: A SAR family, providing continuity to established applications and to interferometry in particular.
- Sentinel 2: A superspectral imaging family for terrestrial applications providing continuity to Landsat and SPOT-type measurements (including vegetation).
- Sentinel 3: An ocean monitoring family, embarking a wide swath multispectral sensor as well as an altimeter.
- Sentinel 4: A geostationary family for atmospheric composition monitoring and transboundary pollution detection.
- Sentinel 5: An atmospheric composition monitoring family in low earth orbit.
Though the numbering should not indicate a specific
order, it is argued that the SAR-Sentinel, planned to be
launched as early as 2007/08, has a priority to continue
with the C-Band observations of ESA satellites so far.
Applications of SAR with proven commercial benefit,
such as differential interferometry and ocean services, have demonstrated the need to have access to
long term time series and historical archives of the
same sensor data. Deliberately, the sentinels would not
deliver information in the VHR domain. This is left
to the European private and national contributions to
GMES.
In a parallel effort, ESA has approached the complexity
of the earth observation ground segment especially
of those technical systems inherited from a
mission-specific design. In a programme aiming for
an Open and Operational (or O2 for short, hence programme
name OXYGEN), ESA and the national ESA
facilities start to address the needs of the future systems
and the demands on information products by
GMES.
Priority is given to the interoperability especially of
those systems supporting the users (catalog, archive,
etc.) and the multi-mission character of the basic
ground segment systems. The interoperability shall
also cover the exchange of data and information with
non-ESA systems, such as with national missions and
the meteorological community and with non-space
data.
The precise design of and interfaces to the GMES
services are still under discussion. Here, the interests
and capabilities of the—partly commercial—service
operators, non-space data players and international cooperation need to be considered. Though,
it seems to be a consensus that all critical systems
shall be based on open, non-proprietary standards and
shall not depend on one single entity or contractor.
Room shall be given to introduce innovative ideas and
services especially in the commercial domain. [1]
References
[1] G.Schreier, S.Dech
"High resolution Earth observation satellites and services in the next decade - A european perspective".
