Vertical Datum and Landsat

Data. This should be done over an ethernet connection.

Get a Landsat TM8 scene covering the Sheep Range of Nevada. Pick a scene with no clouds, at the south end of the range. The download should be about 900 MB, and will uncompress to about 2 GB Compress/Decompress has an option to uncompress the files from USGS (Unix tar.gz file), and place them in a directory with the file name.
Download inside MICRODEM and automatically unzip: Plate tectonics data, on the Options form, geology tab. This will give vertical datum support files.
The global DEMs will be shared with you on the Google Drive. You should unzip them in c:\mapdata\global_dems, and insure they are not buried two levels deep (c:\mapdata\global_dems\global_dems), which is a common windows trick to confuse you when unzipping a compressed folder.

Deliverables

Using the USGS NED as ground truth, compare the others. You should have at least 4 different graphics to support your analysis, and should also consider the visual quality. Pick what you think is the best and worst.
- Did any of the DEMs require an adjustment to be able to make the comparison?
- Was there any improvment in the 1" data compared to the 3" data, to justify the almost 10 times increase in file size?
When you do 3D draping of the Landsat, can you see any difference between the "best" and "worst" DEMs (do not consider the NED).

The two USGS DEMs provide ground truth, for the "true" characteristics of the terrain. We are also looking at the vertical datums. Most of these come in 1 degrees tiles, and they have been modifited slightly for you (mainly so the file names indicate the data set). The rest of the DEMs are free with global coverage; there are higher resolution commercial alternatives.

DEM--Description	Spacing	Source	Producer	Characteristics
NED/3DEP	1/3"	Best available	USGS	Name of the file is the NW corner; others are the SW corner. These still say NED, and the metadata says the name change was cosmetic only.
NED/3DEP	1"	Best available	USGS	Name of the file is the NW corner; others are the SW corner. Just better spatial resolution compared to 1/3".
SRTM	1"	Radar	NASA	Does not cover high latitudes.
ALOS World 3D, AW3D30	1"	Stereo pan imagery	JAXA
NASDADEM	1"	Radar	NASA	Two beta versions, with and without hole filling; Reprocessing of SRTM.
ASTER GDEM	1"	Stereo NIR imagery	NASA / JAXA	Goes closer to the poles than SRTM.
MERIT	3"	Radar + stereo pan	Univ. Tokyo	Combines ASTER and SRTM. This has 5 degree tiles.
Tandem_X	3"	Radar	DLR	Derived from much higer resolution data, only available commercially or by application for research.

Load project There is a project file in the GLOBAL-DEMS folder which will all open the DEM all in one step.

You can deal with 5 degree square DEM.

On one of the other DEMS, go to File, Match other maps, This coverage area.
Return to the 5 degree tile, and File, Save, Current subset MD DEM
File, Save project

Compare the global DEMs, using the NED/3DEP as ground truth.

Multiple DEM profiles, and get a legend. See if the differences appear random or have a pattern (could they be on different vertical datums, is one a DSM and another a DTM?)
Grid correlations map for the DEMs, from the Raster GIS menu.
Scatterplot of two grids, from the Raster GIS menu.
Map Algebra, Difference maps.

Open DEM to open a geoid file, which will be in C:\mapdata\geology\geology_grids\egm2008.tif. (or open it from the Geology menu). This shows + values where the geoid is above the ellipsoid, and - values where the geoid is below the ellipsoid. You can use this to do a vertical datum shift, but the geoid grid does not have to be open.

New image for the Landsat image. Open all bands as a group by picking the TIF file for any one of them.

Landsat scene displays.

Band, and get true color and false color.

Include the following 3D views with the Landsat draped over the DEM. These will work best on a large map

Anaglyph (ask instructor for glasses)
- You can turn off anaglph mode with Right click, 3D map options.
OpenGL 3D view. If the icon is not available, set the DEM to use with the image on Modify menu.
Perspective views

Last revision 10/20/2018