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An Inventory of SRTM-DEM Versions

posted by Satri on Tuesday July 24, @02:45PM        Permalink  Trackback URI  Slashdotthis  Diggthis  Del.icio.us
from the data-data-everywhere-and-the-albatros dept.

I invite everyone to comment and improve this tentative to gather relevant information on SRTM-DEM data and versions. The objective is to build an inventory of the different SRTM-DEM versions. Versions considered are those which (1) do not degrade the spatial resolution of the original dataset and (2) which maintain the original near-global coverage. Read more below.

** Objective **
Build an inventory of the different SRTM-DEM versions. Versions considered are those which (1) do not degrade the spatial resolution of the original dataset and (2) which maintain the original near-global coverage.

 
** General information **
The SRTM-DEM is a near-global coverage topography dataset produced from radar interferometry using C-band radar data acquired by the American space shuttle Endeavour in February 2000. This elevation data covers the globe from latutide 56 °S to 60 °N and is freely available at the 1 arc-second (~30m) spatial resolution over United-States and 3 arc-second (~90m) spatial resolution elsewhere. It is the highest spatial resolution existing DEM data with near-global coverage.

 
** SRTM-DEM versions**
The original SRTM-DEM has 'holes' anywhere topography changes abruptly such as mountainerous areas, and is noisy over water bodies. The data has been edited and a 'finished version 2' has been released which "exhibits well-defined water bodies and coastlines and the absence of spikes and wells (single pixel errors), although some areas of missing data ('voids') are still present". The original SRTM data can be downloaded at ftp://e0srp01u.ecs.nasa.gov/srtm/ in the HGT format.

 
SRTM-DEM data can be downloaded from the GLCF website (http://glcf.umiacs.umd.edu/data/srtm/) on a tile-by-tile basis. Unfinished SRTM datasets have missing pixels which were set by the JPL at value -32768. Their technical guide. We learn from this other document that "[the SRTM-DEM] Version 2 is the results of a substantial editing effort by the NGA and exhibits well defined water bodies and coastlines and the absence of spikes and wells (single pixel errors), although some areas of missing data (‘voids’) are still present".

 
This CGIAR-CSI SRTM website host a whole copy of SRTM version 3 which is said to to be a significant improvement over the version 2. This site also provides precious information on data processing methodology for SRTM version 3. This seems to be the most up-to-date and best SRTM-DEM version.

 
Also of interest (?) are the manually updated SRTM-DEM tiles found here, but however does not include improvements over North America.

 
** Questions **
- Are there other sources of SRTM-DEM improved versions?
- Is the CGIAR-CSI version 3 really the best global version available?
- Will a near-global DEM be generated from the recently launched TerraSAR-X?

 
** Main sources **
Official NASA SRTM site - http://www2.jpl.nasa.gov/srtm/
Additional NASA information - ftp://e0srp01u.ecs.nasa.gov/srtm/version2/Document ation/SRTM_Topo.pdf
Wikipedia SRTM entry - http://en.wikipedia.org/wiki/SRTM
Global Land Cover Facility - http://glcf.umiacs.umd.edu/data/srtm/
USGS SRTM website - http://srtm.usgs.gov/
CGIAR-CSI website - http://srtm.csi.cgiar.org/

 
** TO-DO **
- Update the Wikipedia entry.

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• CleanTopo2

  (Score:2, Informative)

  by hummer010 (162) on Tuesday July 24, @05:50PM (#1590)

  Tom Patterson has a product called CleanTopo2 which is a merger and clean up of SRTM30 Plus data with ETOPO2 data. Check it out at: http://www.shadedrelief.com/cleantopo2/index.html [shadedrelief.com]
  • Re:CleanTopo2

    (Score:3)

    by Satri (3) on Tuesday July 24, @05:58PM (#1591)
    ( http://alexandreleroux.blogspot.com/ | Last Journal: Friday March 17, @05:07PM )

    Thanks!
    
    This CleanTopo2 has a grid resolution of 30 second which is roughly one kilometer, not what I'm looking for, but nice find! :-)

    [ Parent ]
• You have asked a good question

  (Score:2, Interesting)

  by sschwab (1237) on Wednesday July 25, @11:04AM (#1594)

  Searching for available worldwide DEM has been a chore of mine, but I don't have much more advice then just SRTM. Currently we are using SRTM version 2, in DTED Level 1 format, in our production of orthorectified imagery. While it has larger holes in northern Africa, and gaps in some mountain ranges, so far, it is the most affordable ($60 per DVD, set of 13 DVDs, from the USGS) source we have found. Our testing of its accuracy over a known test range has shown that in those areas, it is surpassing its specs.

  Thanks for the link to the CIAT data, I have just started evaluating its use.

  Hopefully, someone knows a hidden cache of great DEM.

  =Schwab=
• HydroSHEDS

  (Score:2)

  by Satri (3) on Wednesday July 25, @02:00PM (#1598)
  ( http://alexandreleroux.blogspot.com/ | Last Journal: Friday March 17, @05:07PM )

  Someone on the Applied-GIS-RS list [matox.com] pointed to the USGS HydroSHEDS SRTM-DEM derivative [usgs.gov].
• CGIAR is the winner and v4 coming soon

  (Score:2)

  by Satri (3) on Monday August 20, @01:52PM (#1654)
  ( http://alexandreleroux.blogspot.com/ | Last Journal: Friday March 17, @05:07PM )

  I contacted the scientists behind Hydrosheds and they clearly favored the new CGIAR's versions unless the goal is hydrology. They also told me version 4 of the CGIAR SRTM-DEM dataset should be available in the coming weeks.
• Wikipedia entry updated

  (Score:2)

  by Satri (3) on Tuesday August 21, @10:28AM (#1656)
  ( http://alexandreleroux.blogspot.com/ | Last Journal: Friday March 17, @05:07PM )

  Not perfect, but more informative now: the SRTM-DEM wikipedia article [wikipedia.org].
• TIN-based void filling article

  (Score:2)

  by Satri (3) on Tuesday September 04, @08:54AM (#1685)
  ( http://alexandreleroux.blogspot.com/ | Last Journal: Friday March 17, @05:07PM )

  On the subject, here's an article named "Filling the voids in the SRTM elevation model — A TIN-based delta surface approach" in the ISPRS Journal of Photogrammetry and Remote Sensing. Link one [sciencedirect.com], link two [sciencedirect.com]. In short, this technique works better than the CIAT one.