Global Land Topography and Ocean Bathymetry from Radar Altimetry
Diane Defrenne(1) and Jerome Benveniste(2)
Via Galileo Galilei ,
00044 FRASCATI ,
(2) ESA, Via Galileo Galilei, 00044 frascati, Italy
The main objective of this work was to generate a new Digital Elevation Model for ENVISAT with a 5- arcminutes per 5- arcminutes grid spacing. This Global Model was achieved by integrating a Bathymetry model built by Walter Smith from NOAA Geosciences Lab and David Sandwell from Scripps Institution of Oceanography, USA with the Altimetry Corrected Elevations (ACE) produced by Philippa Berry of De Montfort University, UK. Both models were used because they present the advantage of associating satellite global altimetry grid with field datasets (depth sounding for the bathymetry and local DEM for the altimetry). To take full advantage of the resolution of both input datasets, two other DEM were also produced with a respective grid spacing of 2 arcminutes and 30 arcseconds.
To obtain a final model with a full, dense and homogeneous coverage, that includes all the information from the initial models and preserves their accuracy, a merge of the data sets was performed carefully respecting the boundary between land and ocean because both original grids had different resolutions. Then, the entire dataset was divided in small geographical tiles that were separately triangulated and interpolated. Edge effects were avoided by taking in consideration an overlap boundary zone. Finally, three grids were obtained at different resolutions, 30 arcseconds, 2 arcminutes and 5 arcminutes (respectively, 1, 4 and 10 km approximately) to be used for applications requiring different scales. All the processing composed by merging of both input datasets and the re-griding at different resolutions was performed using IDL (Interactive Data Language) to benefit of its map visualization and processing capabilities.
These global grids are the first models including essentially satellite radar altimeter measurements of land elevation and ocean bathymetry merged together, giving a unity and a complete, dense and homogeneous coverage of the world, with an unprecedented accuracy.
This new global model at 5-arcminutes resolution will replace the previous model used in ENVISAT data processing and the model at 30-arcsecond resolution will be also used for MERIS and ASAR application projects.