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Tuesday, January 15, 2019

Free DEM Data Sources – Digital Elevation Models

1 Space Shuttle Radar Topography Mission (SRTM)

NASA only needed 11 to obtain their impeccable SRTM 30-meter digital elevation model of the Earth.

The SRTM payload was equipped on the Space Shuttle Endeavour back in February 2000. Using two radar antennas and a single pass, it collected sufficient data to generate a digital elevation model using a technique known as interferometric synthetic aperture radar (inSAR). C-Band penetrated canopy cover to the ground better but SRTM still struggled in sloping regions with foreshortening, layover and shadow.
 n late 2014, the highest possible resolution SRTM data was released to the public. This 1-arc second global digital elevation model has a spatial resolution of about 30 meters covering most of the world with absolute vertical height accuracy of less than 16m.
Where can you download the SRTM data?
SRTM DEM data is being housed on the USGS Earth Explorer. To download, select your area of interest. Under the data sets tab, select  Digital Elevation > SRTM > SRTM 1-ArcSecond Global . But here’s a USGS Earth Explorer download guide to help you get started.

2 ASTER Global Digital Elevation Model

A joint operation between NASA and Japan was the birth of Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER). As part of this project emerged the ASTER Global DEM.
ASTER GDEM boasted a global resolution of 90 meters with a resolution of 30 meters in the United States. Despite its high spatial resolution and greater coverage (80% of the Earth), users were dissatisfied with it because of its artifacts, which often occurred in cloudy areas.
ASTER used stereoscopic pairs and digital image correlation methods. Two (passive) optical images were acquired with different angles taken from the same pass of an airplane. These visible and near-infrared bands of ASTER were affected by cloud cover. This wasn’t the case for SRTM’s C-Band radar. Here’s how passive and active sensors are different.

However, over time, ASTER DEM data has improved its products with artifact corrections of their own. During October 2011 ASTER version 2 of Global Digital Elevation Model was publicly released, which considerably improved on version 1.
Despite being an experimental grade, ASTER version 2 can be considered a more accurate representation than the SRTM elevation model in rugged mountainous terrain. But you should really take a look for yourself.
Where can you download the ASTER GDEM?
You can download the ASTER DEM data for free from the USGS Earth Explorer. Under the data sets tab, select  Digital Elevation > ASTER.

3 JAXA’s Global ALOS 3D World

The ALOS World 3d is a 30-meter spatial resolution digital surface model (DSM) constructed by the Japan Aerospace Exploration Agency’s (JAXA). Recently, this DSM has been made available to the public.
The neat thing about is that it is the most precise global-scale elevation data at this time using the Advanced Land Observing Satellite “DAICHI” (ALOS) – PALSAR’s L-band. JAXA’s SAR mosaics is an exciting development for global elevation.
Where can you download the JAXA’s Global ALOS 3D World?
In order to obtain this highly accurate DSM, you’ll have to register online through the JAXA Global ALOS portal to download it.

4 Light Detection and Ranging (LiDAR)

You might think that finding LiDAR is a shot in the dark.
But it’s not anymore.
Slowly and steadily, we are moving towards a global LiDAR map.
With Open Topography topping the list at #1, we’ve put together a list of some of the 6 best LiDAR data sources available online for free.
Because nothing beats LiDAR really in terms of coverage and accuracy. Filtering ground returns, you can build an impressive DEM from LiDAR.
…And if you still can’t find anything in the link above, try your local or regional government. If you tell them what you are using it for, they sometimes hand out LiDAR for free.

5 Mars Orbiter Laser Altimeter (MOLA)

Just throwing this out here to peak your interest.
Earth isn’t the only surface being mapped for elevation.
You can go for a spin on the rugged terrain of Mars using data captured by the Mars Orbiter Laser Altimeter (MOLA) instrument as shown in the Mars Terrain map.
In fact, the data captured from the MOLA instrument data was used to map out ancient streams on Mars. If this doesn’t excite you, I don’t know what would.

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