Help - GETASSE30 Elevation Model

GETASSE30 Elevation Model

GETASSE30 stands for Global Earth Topography And Sea Surface Elevation at 30 arc second resolution. This elevation model has been provided by Marc Bouvet (marc.bouvet@esa.int) of ESA/ESRIN. This documentation is also by courtesy of Marc Bouvet.

The DEM tiles will be downloaded automatically by the software as needed.

The GETASSE30 Data Set

GETASSE30 is a composite of four other DEM datasets. It uses the SRTM30 dataset, ACE dataset, Mean Sea Surface (MSS) data and the EGM96 ellipsoid as sources. The resulting GETASSE30 dataset represents the Earth Topography And Sea Surface Elevation with respect to the WGS84 ellipsoid at 30 arc second resolution. The dataset has no missing values, but at the junction of the arctic and antarctic continents there are some tens of strange negative values (down to -700 m) inherent to the ACE dataset. All latitude/longitude values refer to the center of a pixel, not to one of its corners. The GETASSE30 dataset is organised as multiple tiles.

Example of a GETASSE30 tile

The GETASSE30 Data

Mean sea surface height over sea and height over land, both referenced to the WGS84 ellipsoid.

Resolution:	30 arc second latitude and longitude
Unit:	meter
File name example:	45S045W.GETASSE30 where the first number is the latitude of the most South West pixel and the second number its longitude
Data format:	binary, 1800*1800 signed 16-bit integer values, big endian order

The GETASSE30 elevation data

There are 5 types of values:

Over land, between 60N and -60S, where SRTM30 DEM data are available, the output value is the sum of SRTM30 elevation and the EGM96 geoid height.
Over land, between 60N and -60S, where SRTM30 DEM data are not available, the output value is the sum of ACE elevation and the EGM96 geoid height.
Over land, above 60N and -60S, where ACE data are available, the output value is the sum of ACE elevation and the EGM96 geoid height.
Over sea, where neither ACE DEM nor SRTM30 data are not available, if MSS data are available, then the output value is the MSS.
Over sea, where neither ACE DEM nor SRTM30 data are not available, if MSS data are not available, then the output value is the EGM96 value.

Flag

Pixels described as in 2) and 3) are flagged with the value 0
Pixels described as in 3) are flagged with the value 1
Pixels described as in 4) are flagged with the value 2
Pixels described as in 1) are flagged with the value 3

Resolution:	30 arc second latitude and longitude
Unit:	none
File name example:	45S045W.GETASSE30_flag where the first number is the latitude of the most South West pixel and the second number its longitude
Data format:	binary, 1800*1800 unsigned 8-bit integer values, big endian order

The flag associated to the GETASSE30 data

Input Data used in GETASSE30 Generation

ACE DEM at 30 arc second resolution referenced to the EGM96 geoid
See ACE Report at http://www.cse.dmu.ac.uk/geomatics/products_ace_overview.html
SRTM30 data are reference to the EGM96 geoid
See http://www2.jpl.nasa.gov/srtm/
Mean Sea Surface (MSS) height at 2 minutes resolution referenced to the WGS84 ellipsoid.
From the RA2 auxiliary file RA2_MSS_AXVIEC20031208_145545_20020101_000000_20200101_000000
See RA2 product handbook at http://www.ENVISAT.esa.int