A regional scale extend for absolute altimeter sea surface height calibration. Impact of MOG2D Barotropic gravity wave model
Abstract
Absolute calibration of sea surface height (SSH) measurements derived from space borne radar altimeters is usually done with respect to concomitant sea level in-situ records provided by tide gauges or GPS buoys directly below the satellite [Ménard et al 1994, Haines et al 1996, Bonnefond et al 2003]. Such a method allows a regular and long term control of the sea level with independent records, however this is a single point geographically dependent approach. In order to obtain a more significant and a more precise bias, there is a strong interest in extending the calibration area and the number of calibration opportunities. We propose to present some results from a new method that was developed to extend the single-point approach to a wider regional scale, taking advantage of the nearest calibration site instrumentation. The idea is to compare sea level from altimeter and tide gauge that are not only along the satellite ground track but also at distant points onto adjacent passes. Connecting sea level satellite data with distant in-situ data requires to correct from the marine geoid slope and from the ocean dynamics differential effect. The geoid slope is derived from distant SSH altimetric data. They are propagated along a succession of known altimetric mean sea level profiles (Topex-Poseidon /Jason) up to the in-situ reference site. The ocean dynamics differential effect, which is becoming larger as the distance from the site is increasing, is provided by the barotropic gravity wave ocean model MOG2D (Le Provost, Lyard et al. 1994). This method was first validated with Jason-1 GDR data in Corsica, taking the Senetosa site as the reference ; Then applied to TOPEX/POSEIDON on its new orbit and to Geosat Follow On. Convincing and accurate results have been obtained emphasizing all the benefit which can be gained from such a method, allowing to multiply significantly the number of altimeter calibrations over dedicated sites or over distant sites. Such a method is applicable to any altimeter in different areas, assuming that there is calibration site with levelled tide gauges and an accurate mean altimeter profile available within the investigated region.
- Publication:
-
35th COSPAR Scientific Assembly
- Pub Date:
- 2004
- Bibcode:
- 2004cosp...35.4245G