Application of multi-mission altimeter measurements to the analysis of wave height time and space variability over the Mediterranean Sea.
The ability of satellite altimeters to measure the significant wave height (swh) has been demonstrated. Since 1991 six altimeters have been launched and, today, five altimeters are in operation. An effort for cross validation of swh measurements from the various missions has been performed and, now, intercalibrated altimeter swh data are available over almost a 15 year time period. This long term data set can be used to analyse the time and space variability of swh over the oceans. This paper presents such an application over the Mediterranean Sea. This study can be extended to any other regional or global analysis.
Firstly, the results of a global long term validation activity are summarized, allowing to correct swh measurements from the various missions, providing an homogeneous data set.
Secondly the 13 years (September 1992 to September 2005) of TOPEX and Jason swh measurements along the initial TOPEX orbit are analysed. Instead of collecting all the altimeter data available over a particular area to infer statistical description of swh, the data are collected along each ground track at a regular 0.05° sample in latitude. One advantage is to be able to detect short spatial scale variability. The main drawback is the poor time sampling, one pass every 10 days - this is illustrated using the data from the ERS-1 3-day repeat cycle phase A. Nevertheless it is shown that, over a long time period, seasonal spatial variability of swh can be estimated over the various basins of the Mediterranean Sea.
In a third part the swh time variability is estimated, by analysing the multi-mission (ERS-1&2, TOPEX Poseidon, GEOSAT FO, Jason-1 and ENVISAT) data set available over the various Mediterranean basins. The impact of the number of altimeters is analysed. Differences of swh time variability over the various basins is analysed and shown to be linked to the various specific regional short scale wind regimes over the Mediterranean Sea.