7
$\begingroup$

I would like to find sources of topographical data for Earth's surface.

I've looked in GIS SE and Open Data SE but haven't found a good answer to this so I though I'd ask here in Earth Science.

  • Are there public sites where I can download free topographical data; tables of surface height above a reference surface?

  • Is it possible to download them in text or tabular form?

I'm looking for resolution of something of the order of 5 meters vertically an 10 horizontally, but there's no specific hard requirement.

$\endgroup$
  • $\begingroup$ SRTM is available. It is in binary form or the .hgt format. I think converters are available . $\endgroup$ – gansub Mar 20 '19 at 7:15
  • $\begingroup$ @gansub interestingly I believe that that's the exact data in my linked answer I'll add a sentence to point that out. $\endgroup$ – uhoh Mar 20 '19 at 7:17
  • 1
    $\begingroup$ Look at my answer below, if you are interested in Taiwan, perhaps ALOS W3D would be a good option. In some areas I'm interested in, it has a lot of gaps, but in that area I guess they acquired more images and should be pretty good. $\endgroup$ – Camilo Rada Mar 20 '19 at 20:36
8
$\begingroup$

This is an interesting and common question, so I'll try to give a good answer here, that I think is a good place, as well as GIS and Open Data SE. First, regarding the format, you will never find data natively stored in text or tabular form, because the large data volume would lead to huge files very difficult to handle. Data is usually stored in binary files, common standards are .hgt and .tif. And there are many software and utilities that can export small subsets of the data into text, csv, or tabular formats.

I'll list here the global or near to global sources. All of them have advantages and disadvantages, and all have data gaps and artifacts, specially in areas with rough topography. So depending of your area of interest, one or the other can be better.

SRTM (Shuttle Radar Topographic Mission)

Resolution: 1 arc-sec (~30 m)
Data epoch: February 11$^{th}$ to 22$^{nd}$ 2000 Data type: Integer Vertical reference: Orthometric (geoidal)

The most widely used standard, due to its quality, resolution, and coverage. It covers the whole globe between latitudes 60°N and 56°S.

enter image description here

In contrast to all other datasets, all the data was acquired in a 11-day mission, therefore, it have unmatched consistency, specially in areas with rapid terrain changes like glaciers, open pit mines, cities, etc.

The space shuttle was carrying two radars that created two independent terrain models, the coverage above corresponds to the SAR-C instrument that produced the data that is most widely used. The second instrument was the X-SAR, that had a narrower swath, and does not have global coverage.

There are multiple versions of these datasets:

SRTM v3

The latest official release is version 3. It comes in its original form, that includes data gaps and a gap-filled version, on which those gaps have been filled with data coming from multiple sources (but primarily ASTER GDEM).

The data can be accessed through multiple gateways, some of them are:

USGS EarthExplorer
NASA EarthData
LP DAAC Global Data Explorer USGS data server (Version 2.1)

CGIAR SRTM

An independent post-processing of SRTM data. Known also as SRTM v4. It consists of a gap-filled version of SRTM using an advanced algorithm. It is only available at 3 arcsec resolution (90 meters) . It can be downloaded at the CGIAR SRTM Download manager

NASADEM

The SRTM data was reprocessed with cutting edge technology, improving accuracy and reducing data gaps. In contrast to other SRTM versions, it offers also a ellipsoidal version of the data (instead of geoidal), and the data comes in floating point values (instead of integers). NASADEM is expected to be the last official release of SRTM data. This DEM is still in the development phase but should be released at any time. A provisional version has been released and can be downloaded at the MEaSUREs data repository. More information on how to use this data can be found in my answer here.

This dataset should NOT be confused with the "NASA Shuttle Radar Topography Mission Global 1 arc second V003" (SRTMGL1). Which corresponds to the SRTM v3 data described above.

ViewFinderPanoramas

Some individuals like Jonathan de Ferranti, tackled the gargantuan task of doing a manual quality assessments of all the gaps of the SRTM and areas that have erroneous data. To then fix it using many sources, including many national mapping agencies from around the world. He produced a great version of SRTM with most errors fixed. Unfortunately, all this work was done before the worldwide release of full resolution SRTM data in 2014, therefore, for most of the world this data have only 3 arc-sec resolution (~90 m). And it can be downloaded at ViewFinderPanoramas.org.

SRTM X-SAR

Data from the second radar on board the Endevour space shuttle during the SRTM mission. It has slightly higher resolution (~20 m) but worst coverage, because the multiple swaths did not overlap, so for example, over North America the coverage looks like this:

enter image description here

This data can be downloaded from DLR Geoservice.

ASTER GDEM

Resolution: 1 arc-sec (~30 m)
Data epoch: 2000 to 2011 Data type: Integer Vertical reference: Orthometric (geoidal)

With almost complete coverage between 83°N and 83°S, GDEM was produced from more 1.5 million stereo pair images by ASTER sensor. A joint project between JAXA and NASA on board of Terra satellite. This is the coverage of the latest release:

enter image description here

The current version is GDEM v3 (released on August 5 2019). This Release also includes the ASTER Water Body Dataset (ASTWBD), a valuable dataset to correct terrain models. GDEM v3 is available from:

NASA EarthData
Japan Space Systems

ALOS World 3D

Resolution: 5m (paid), 30 m (free)
Data epoch: 2006 to 2011 Data type: Integer Vertical reference: Orthometric (geoidal)

Somehow the successor of ASTER, ALOS and its instrument PRISM, also offer stereo capability and higher resolution. And it was used to generate a new DEM with near global coverage:

enter image description here

The free 30 m resolution version of the data (with maximum resolution of 5 m), can be downloaded at JAXA AW3D30 DSM data page (need to sign up first). Current version is AW3D30 v2.2 (released in April 2019).

GSDEM30

The "Global Seamless DEM 30" is a 1-arcsec (~30 m) DEM that was constructed by merging unfilled SRTM, ALOS World 3D, and ASTER GDEM v2 datasets. By combining all these sources, it reduces data-gaps and significantly improves the quality of the data in regions where any of the base DEMs performs poorly. Data can be downloaded from the Wuhan University's SENDIMAGE servers. More details of the data merging process can be found in this paper.

TanDEM-X WorldDEM

Resolution: 12m (paid), 90 m (free)
Data epoch: 2010 to 2015 Data type: Floating point Vertical reference: Ellipsoidal

The latest radar base global elevation model, created from two satellites orbiting in tandem formation (TanDEM-X), allowing high accuracy single-pass InSAR and DEM generation with truly global coverage. The free 90 meter resolution data can be downloaded from DLR Geoservice.

ArticDEM and REMA

Resolution: 2m
Data epoch: 2007 to 2018

This two projects turned the polar areas from being the ones with the worst available topographic data to the ones with the best data. By computing DEM's from millions of stereo image pairs from the high-resolution imaging satellites of DigitalGlobe. ArticDEM covers all latitudes north of 60°N:

enter image description here

And REMA covers all latitudes south of 60°S:

enter image description here

The data can be explored and downloaded from the ArcticDEM Exporer, and Antarctic REMA Explorer.

| improve this answer | |
$\endgroup$
  • 1
    $\begingroup$ Thank you for the comprehensive answer! I think this will be quite helpful to me and future readers having all of this information in one place. This will keep me busy for quite a while now. $\endgroup$ – uhoh Mar 20 '19 at 21:42
  • 1
    $\begingroup$ @uhoh I agree. I think it will be a good reference for myself too. I had often found myself looking for those download links. For the same reason it might be a good idea to edit the question to something more generic. The info of previous versions might be superfluous. $\endgroup$ – Camilo Rada Mar 20 '19 at 22:32
  • 1
    $\begingroup$ I absolutely agree. Have a look at the edit, feel free to edit further if necessary. Thanks! $\endgroup$ – uhoh Mar 21 '19 at 0:45
  • 1
    $\begingroup$ Thanks for this great answer. It will certainly prompt me to download soem of the data and play with it. $\endgroup$ – MyCarta Mar 22 '19 at 20:28

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.