Help Content > Import Data > DEM Extraction > GLAS

Purpose

The following Digital Elevation Models can be imported:

-	Antarctic area (500 meters resolution).

-	Antarctic area (1 kilometer resolution).

-	Greenland area (1 kilometer resolution).

Technical Note

The Geoscience Laser Altimeter System (GLAS) instrument on the Ice, Cloud, and land Elevation Satellite (ICESat) provides global measurements of elevation, and repeats measurements along nearly-identical tracks; its primary mission is to measure changes in ice volume (mass balance) over time.

These DEMs are generated from the first seven operational periods (from February 2003 through June 2005) of the GLAS instrument. They are provided on polar stereographic grids. The grids cover all of Antarctica north of 86° S and all of Greenland south of 83° N. Elevations for both ice sheets, originally reported as centimeters above the WGS 84 Ellipsoid, are scaled to meters for a better use in the SARscape processing chain.

More detailed information on this project are available through NSIDC (National Snow and Ice Data Centre). This Institute is acknowledged for the provision, and free distribution, of these data.

The relevant "Input file" and corresponding headers must be downloaded via FTP, using the following addresses:

-	Antarctic area (500 meters resolution) > ftp://sidads.colorado.edu/pub/DATASETS/DEM/nsidc0304_icesat_antarctic_dem

•NSIDC_Ant500m_wgs84_elev_cm.dat.gz (data file); it must be decompressed and then entered as "Input file".

•NSIDC_Ant500m_wgs84_elev_cm.dat.hdr (header file); it must be stored in the same folder of the decompressed "Input file" in order to be automatically read by the program.

-	Antarctic area (1 kilometer resolution) > ftp://sidads.colorado.edu/pub/DATASETS/DEM/nsidc0422_antarctic_1km_dem

•krigged_dem_nsidc.bin (data file); it must be entered as "Input file".

•krigged_dem_nsidc.bin.hdr (header file); it must be stored in the same folder of the "Input file" in order to be automatically read by the program.

-	Greenland area (1 kilometer resolution) > ftp://sidads.colorado.edu/pub/DATASETS/DEM/nsidc0305_icesat_greenland_dem

•NSIDC_Grn1km_wgs84_elev_cm.dat.gz (data file); it must be decompressed and then entered as "Input file"

•NSIDC_Grn1km_wgs84_elev_cm.dat.hdr (header file); it must be stored in the same folder of the decompressed "Input file" in order to be automatically read by the program.

The products are imported using their native Polar Stereographic projection. It is suggested to keep the original cartographic reference system.

Interpolation

Two interpolation methods can be used to assign a value to dummy (i.e. NaN) pixels :

–Relax Interpolation - This approach works well for small areas, hence it can be used for interpolating the Greenland DEM (dummy areas made of one or very few pixels); the method, which applies an algorithm based on the solution of the heat transfer equation (Poisson equation), adopts a soft surface and adapt it to the dummy surrounding area. Viersa the Antarctica DEM, which contains a very large area with null values in its center (South Pole surroundings), cannot be interpolated with this method.

–Mean Interpolation - This approach can be used, by properly setting the window dimension. Dummy pixels are replaced with valid values if the window size is large at least as the dummy area to be filled.

Note: Subtract Geoid (Other Parameters)

By setting this flag the output product will be referred to the ellipsoid. The EGM96 geoid is subtracted. Set this flag if the extracted Digital Elevation Model has to be used for further processing in SARscape.

Input Files

Input file

Name of the file to be imported (.dat file previously decompressed or .bin file). This file is mandatory.

Parameters - Principal Parameters

Subtract Geoid

Slope

By setting this flag, three slope files are created: slope east-west, slope north-south in degree between -90 and 90. The third out is the absolute slope (sqrt(ew^2 +ns^2)) in degree, between 0 and 90 degree.

Relax Interpolation

Set this flag to apply the relax interpolation method (see Technical Note).

Mean Interpolation

Window dimension used to interpolate the input null values (see Technical Note). If zero is entered, the interpolation is not carried out.

Parameters - Global

It brings to the general section of the Preferences parameters. Any modified value will be used and stored for further processing sessions.

Parameters - Other Parameters

It brings to the general section of the Preferences parameters. Any modified value will be used and stored for further processing sessions.

Output Files

Output file

Output file name of the extracted Digital Elevation Model. This file is mandatory.

_dem

Imported Digital Elevation Model, with user-defined projection and grid size, and associated header files (.sml, .hdr).

_W2E_slope

Easting direction slope image and associated header files (.sml, .hdr).

_S2N_slope

Northing direction slope image and associated header files (.sml, .hdr).

_slope

Combined slope image and associated header files (.sml, .hdr).

These last three files are generated only if the relevant flag is set..

Details specific to the Units of Measure and Nomenclature of the output products can be found in the Data Format section.

General Functions

Exec

The processing step is executed.

Store Batch

The processing step is stored in the batch list. The Batch Browser button allows to load the batch processing list.

The window will be closed.

Help

Specific help document section.

Specific Function(s)

None.

General Tools - Digital Elevation Model Extraction - GLAS/ICESat

General Tools - Digital Elevation Model Extraction - GLAS/ICESat