Regional coastal sea level change and sea level topography from altimetry, oceanography, and tide gauge stations in Europe
Zusammenfassung der Projektergebnisse
Goal of the project RECOSETO was to provide improved coastal altimeter data and study the sea level variability in coastal regions and regionally. The standard altimeter data are available starting from about 20-30km from the coast, mainly due to the application of the standard selection criteria and due to the unavailability of some corrections. Using improved selection criteria and ad-hoc analysis of the altimeter signal (re-tracking of waveforms) we have been able to use altimeter data at 3-5 km from the coast (Fenoglio-Marc et al., 2008; Gommerginger et al., 2009). We have shown that the usual open ocean validity checks are too restrictive near coast and improved data screening strategies avoid removing too many data. Most of the data elimination is due to the checks on the microwave radiometer wet tropospheric correction and on the standard deviation of the 18 Hz retracked ranges for Envisat. We have concluded that Envisat performs better in coastal regions than Topex/Poseidon. At sea-land transitions the performance is better than at land-sea transitions. Envisat data have been then retracked with a set of empirical retracking algorithms, and improvements are obtained by using the Beta-5 and the Improved Threshold retracker methods. Statistical methods have been used to represent the regional and global variability. We have investigated the coastal and the global sea level variability between January 1993 and December 2008, with the aim to detect long-term differences. The coastal variability is estimated from tide gauges, altimeter data co-located to the tide gauges, and from altimeter data along the world coasts. The global variability is estimated from altimeter data. A set of 290 tide gauge stations suitable for large-scale sea level change analysis are selected using criteria based on record lengths and proximity with satellite altimetry. We show that the coastal and global spatially averaged time-series have similar long-term trends of 3.1 mm/yr between January 1993 and June 2008. The interannual variability is stronger in the coastal averaged time-series, due to the regional interannual variability and to the fewer number of points used. We find a good agreement between coastal and open-ocean sea level variability, all main world basin have a positive long-term trend. Location, number and distribution of the tide gauge stations and extension of the coasts, play however an important role and explain part of the differences observed (Fenoglio-Marc and Tell, 2009). When considering small sub-basins the trend can be quite different from the global trend (Fenoglio-Marc, 2009) A very interesting result of our project was a detailed analysis of the causes for elimination of data near to the coast. We show that Envisat data are available very near to coast, but standard criteria eliminate most of the data in coastal region. First shown in Fenoglio et al. (2008) we continue the investigation in Bouffard et al. (2009) in cooperation with CNES. The “coastal altimetry” appears to be a very interesting and promising application of altimeter data. The scientific community is intensively working in this direction. The discussion if coastal sea level change is accelerating and greater at the coast than in average is of great interest for the society. Our findings (Fenoglio et al., 2009) study confirm the results fro Prandi et al. (2009). Sea level rise is a public theme. Presentations at days of open doors at the University and in guest lectures at “Graduiertenkollegien” at the TU Darmstadt and in Schools (Gymnasien) were given. Retracking in coastal region appears to be promising to increase the number of data near to coast. The Empirical retracking methods we have used are suitable near coast and can be improved further. High-frequency data have to be used near coast. Other groups are developing alternative methods of retracking. New coastal database are now in preparation and available for tests against our own methods. In particular coastal data can greatly improve the geoid near coast. This application was intended in Task 4 of our proposal and could not be sufficiently considered due to the time limits. It is possible now that data are available near to coast from this project, A follow on proposal on “coastal altimetry” is therefore of great interest. Various collaborations are made possible by previous RECOSETO.
Projektbezogene Publikationen (Auswahl)
- (2007) Envisat waveform retracking over the Mediterranean, TUD UR N.1
Gao YG.
- (2007). An assessment of satellite altimetry in proximity of the Mediterranean coastline, ENVISAT Symposium
L. Fenoglio-Marc, S. Vignudelli, P. Cipollini, M. Becker , M. Fehlau
- (2007). An assessment of satellite altimetry in proximity of the Mediterranean coastline, in 3rd ENVISAT Symposium Proceedings, SP-636, ESA Publications Division
Fenoglio-Marc L., S. Vignudelli, A. Humbert, P. Cipollini, M. Fehlau and M. Becker
- (2008) Coastal altimetry, International Geoscience and Remote Sensing Symposium (IGARSS), Coastal Altimetry session, Boston
Fenoglio-Marc L.
- (2008) Coastal sea level heights from improved altimeter data in the Mediterranean Sea, TUD IR N. 2
Croce-Ferri L.
- (2008) Sea level variability in the North Adriatic from satellite observations, Workshop: “The climate in the Venetian and North Adriatic region: variability, trends and changes”, Venezia, October, P. Lionello
Fenoglio-Marc L.
- (2008). Coastal sea surface heights from improved altimeter data in the Mediterranean Sea, EGU
Fehlau M., L. Ferri, L. Fenoglio, Y. Gao, M. Becker
- (2008). Coastal Sea Surface heights from improved altimeter data, in IGARSS Proceedings, Boston, IEEE International, Geoscience & Remote Sensing Symposium
Fenoglio-Marc L., M. Fehlau, S. Vignudelli and M. Becker
- (2008). Comparison of improved altimeter coastal sea surface heights to tide gauge DATA, 2nd Coastal altimetry Workshop, Ocean Sea Surface Topography Science Team, Nice
Fenoglio-Marc L., M. Fehlau, M. Becker, S. Vignudelli and J. Bouffard
- (2008). Tracking and Retracking, International Workshop on Coastal Altimetry, Washington
Smith W, P. Berri and L. Fenoglio-Marc
- (2009). Coastal sea surface heights from improved altimeter data and effect of coastal local characteristics, 3rd Coastal altimetry Workshop, Frascati, ESA
Fenoglio-Marc L., M. Becker
