7.3 The 2-Minute Gridded Global Elevation Data ETOPO2

ETOPO2 is a global data base of topography and bathymetry on a regular 2-minute grid. It is a compilation of data from a variety of sources. It can be downloaded from the US National Geophysical Data Center (NGDC) web page

http://www.ngdc.noaa.gov/mgg/fliers/01mgg04.html

From the menu bar Free online we select Make custom grids which is linked to the GEODAS Grid Translator. First we choose a Grid ID (e.g., grid01), the Grid Data Base (e.g., ETOPO2 2-minute Global Relief), our computer system (e.g., Macintosh) and the Grid Format (e.g., ASCII for both the data and the header). Next we define the longitude and latitude bounds. For example, the latitude ( lat) from ?20 to +20 degrees and a longitude ( lon) between +30 and +60 degrees corresponds to the East African coast. The selected area can be transformed into a digital elevation matrix by pressing Design a grid. this matrix may be downloaded from the web page by pressing Download your Grid Data, Compress and Retrieve and Retrieve compressed file in the subsequent windows. Decompressing the file grid01.tgz creates a directory grid01_data. This directory contains various data and help files. The subdirectory grid01 contains the ASCII raster grid file grid01.asc that have the following content:

     NCOLS   901     NROWS  1201     XLLCORNER ...