Do we need an International Altimeter Service?

1. Do we need an International Altimeter Service? W. Bosch1) and C.K. Shum2) 1) Deutsches Geodätisches Forschungsinstitut (DGFI), München email: bosch@dgfi.badw.de 2) Laboratory for Space Geodesy and Remote Sensing Research, The Ohio State University

2. Satellite Altimetry • evolved to an operational remote sensing technique with very important applications to many geosciences • Altimetry is a cross-cutting space technique requiring • global, precise and long-term operation with • high spatial - and temporal resolution through • multi-mission operation with • harmonized and cross-calibrated mission data. • Growing demands through new technologies (laser, wide swath, LIDAR, ...).

3. General Accepted Requirement • A long and precise time series of utmost consistent altimeter observations with up-to-date geophysical corrections, consolidated geocentric reference and long-term stability. • This task is • international • interdisciplinary, • mission overlaping, and • agency independent, • all together rationales for an International Altimeter Service

4. Deficienciesproviding additional rationales for an IAS • Users do not have a single point-of-contact! • There are many (!!) different >formats for altimeter data • Increasing data volume and complexity • Orbits and geophysical corrections are not always up-to-date • Reference system relationship and • long-term stability of altimetry not sufficiently solved

5. Altimeter users are already served!There are groups, institutes and agencies, providing excellent value-added altimeter products

6. Examples of Value-Adding (1) • Delft (DEOS)provides highly precise orbits for ERS-1 and ERS-2, in support of altimetric and InSAR research. Orbits and supporting software can be freely downloaded. • AVISO (CLS)harmonized multi-mission data and provides - corrected sea surface heights and - sea level anomalies (along-track and gridded) for TOPEX/Poseidon, ERS-1, and ERS-2 (Jason-1, Envisat)

7. Examples for Value-Adding (2) • NASA Pathfinder harmonized T/P, ERS-1/2 and Geosat and provides „stacked“ data files with sea level anomalies re-aranged for analysis of sea level variations. • PO.DAAC (JPL) provides the T/P data, a dedicated SLA product, and a reformatted ERS-1 data set with improved orbits. (Historical data from Geos-3 and Seasat)

8. Multi-Mission Altimeter Data Bases Provide on-line access to enhanced mission data • RADS (DEOS, Delft) keeps consistent orbits for all missions and updates for most of the geophysical corrections; up-to-date archive; high expertise through involvement in cross-calibration/validation of Envisat/ERS, Jason/T/P, GFO • ADS Central (GFZ, Potsdam) nearly as complete as RADS; updates for many geophysical corrections; alows user defined data base extracts.

9. In Summary: • Satellite Altimetry has multi-disciplinary applications and will become a core element of a Global Earth Observing Systems • The need for long-term, precise and consistent time series of altimeter observation requires to realize synergies from all missions/technologies • These general aspects may be best solved by an International Altimeter Service

10. General IAS Objectives • Serve altimeter users! • there are both, operational and scientific users • user requirements (to be compiled from key documents) • Integrate already existing value-adding entities, asked to • contribute through the provision of data and products • become actively involved and help to develope and configure IAS

11. More specific objectives: IAS should ... • Inform where to get what altimeter data and products • allow (or assist) users to download data and poducts • compile, focus and react to user requirements • collect (or provide) sufficient documentation • assess and illustrate product quality • review product generation and specify new products • recommend improvements for data and products • communicate and interface to other related services

12. IAS Data and Products - a possible wish list 1) • Harmonized multi-mission along-track data (level 2) • results of (cross-) calibration and datum offsets • multi-mission models of the mean sea surface • estimates of the sea surface topography • marine gravity data derived from altimetry • sea level anomaly time series • estimates of ocean mass redistribution (with entities providing estimates of the steric effect) • altimetry @ coastal areas (altimetry@tide gauges) • land & ice application ... 1) certainly not complete

13. What elements are needed for an IAS? • Sensor data generation • Geophysical processing • Quality-control, calibration/validation • Archiving and dissemination • Value-adding product generation • User interface • Scientific advisory • Documentation • Knowledge base, training, education, outreach ?

14. How to organize an IAS? • Organisational elements • centralized versus distributed processing/archiving • Feedback to science and operational users • Hosted by which legal entities? • Commitments, fundings, financial support

15. The Objectives of the IAS Working Group • Study rationale, feasibility and scope of an International Altimeter Service • The IAS-WG should • have a clear focus (expected results, deliverables) • be limited in time (e.g. 4 years) • report about outcomes • Provide a forum for external discussions

16. IAS Working Group • Is looking for integration of & support from • Space agencies & administrations (CNES, ESA, NASA, NOAA, ...) • Scientific Organisations (IAG, IAPSO, IOC, ... • Data/product centres (PO.DAAC, SSALTO/DUACS, DEOS/RADS, ... • Observation systems (GLOSS, GOOS, GTOS, GCOS, IGGOS, ... • Already existing services (IGS, PSMSL, IERS, ...) • Membership of IAS-WG should • represent technologies, systems and applications, but • be limited to be efficient