[OSGeo-Discuss] 30m SRTM worldwide?
troelsgaard53c at live.dk
Fri Aug 26 02:35:51 PDT 2011
I looked around for information about the artefacts in the aster data. The Quality Assessment file that accompanies the data mentions:QuoteThe 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.
UnQuotefollowing the link:http://www.ersdac.or.jp/GDEM/E/image/ASTERGDEM_ValidationSummaryReport_Ver1.pdfAt 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 CarstenSylv 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!
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