[OSGeo-Discuss] 30m SRTM worldwide?

Sylvain JM Desmoulière syltao at gmail.com
Fri Aug 26 15:01:46 PDT 2011

Hi Carsten,

It is almost certain that you are right.

The chapter "C. Residual Anomalies and Artifacts GDEM" detailed
"Artifacts Related to Stack Number Irregular Boundaries."
- Decripiton of the "pits" is similar to more or less circular holes I
see. The text says they "Regularity and Often Occur with high
frequency in Virtually all ASTER GDEM tiles" and "from just a FEW
meters to 100 meters or more." Ok
- The large positive anomalies similar to "mole run" artifacts (p.23
of the text).
- Undoubtedly the linear artifact are "step anomaly" (p. 19 text).

Thank you for your comments, I'll put them on the blog to let things clear.


PS: as you assume, unfortunately, no amazon mystery reveled...


2011/8/26 Carsten Troelsgaard <troelsgaard53c at live.dk>
> I looked around for information about the artefacts in the aster data. The Quality Assessment file that accompanies the data mentions:
> Quote
> The automated cloud masking and statistical approach used to select data for stacking
> are not totally effective in avoiding anomalous elevations values, and anomalies may
> remain in the GDEM where the stack number is three or less, particularly. Where
> available, existing DEMs were used to replace anomalous GDEM values, including
> adjusting for offsets between the ASTER GDEM and the reference DEM data.
> UnQuote
> following the link:
> http://www.ersdac.or.jp/GDEM/E/image/ASTERGDEM_ValidationSummaryReport_Ver1.pdf
> At page ~20 the chapter "Artifacts Related to Irregular Stack Number Boundaries." has additional information and visual displays equal to the ones you link to at //yepka..
> It would be interesting if the artefacts reveal some secret about the landscape, but so far I've treated as a measurement/processing-error.
> I assume that 'stack-number' originates from overlapping measurement-swats
> Carsten
> ________________________________
> Sylv wrote:
> I used a re-sampling to 30m of SRTM-DEM (made by Brazilian INPE) and observe a visual superposition between GRASS-r.watershed river network output and 2001 Landsat7 deforested areas (the nearest date after SRTM) (see http://yepca.org/wp3/?p=349)
> As you suggest, I'll verify if CGIAR SRTM-DEM is better in such flat area with forest/cultivation patchwork.
> In first analyze, ASTER GDEM gave better river network, even with the theses 20-30m holes or larges areas artifacts!... but more job is necessary to verify and understand why!
> Sylv
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