[R-sig-Geo] A new ASTER Global DEM data set

[Tomislav Hengl]

Hi all,

FYI: I've run a small comparison between ASTER DEM and LIDAR DEMs (say 'true' topography):

http://geomorphometry.org/content/gdem-quick-assessment 

The 4 case studies can be downloaded from here:

http://geomorphometry.org/system/files/GDEM_assessment.zip 

I'm not too happy with what I've got - GDEM shows very strange patterns in area of low relief and I
definitively think that the 30 m resolution is overoptimistic; it should be degraded to 60-90 m
(this would enhance the data sharing and save them a lot of trouble). The positional accuracy of
GDEM is on the other hand pretty good.

GDEM is a frankestein - once you zoom in and add some shading, you can see the stitches, so have
this in mind (unlike SRTM DEM which is a complete and a consistent project; but also noisy in many
areas). 

T. Hengl
http://home.medewerker.uva.nl/t.hengl/ 



> -----Original Message-----
> From: r-sig-geo-bounces at stat.math.ethz.ch [mailto:r-sig-geo-bounces at stat.math.ethz.ch] On Behalf
> Of Ashton Shortridge
> Sent: Friday, November 20, 2009 3:15 PM
> To: r-sig-geo at stat.math.ethz.ch
> Cc: Yong Li
> Subject: Re: [R-sig-Geo] A new ASTER Global DEM data set
> 
> On Friday 20 November 2009 07:09:35 Barry Rowlingson wrote:
> > 2009/11/20 Yong Li <yong.li at unimelb.edu.au>:
> > > Dear all folks,
> > >
> > > I was informed in the 6th Digital Earth Conference that there is a better
> > > place to acquire high resolution of global DEM developed by ASTER, called
> > > GDEM with 30 m resolution, and fantastically free of charge. I tried some
> > > here (http://www.gdem.aster.ersdac.or.jp/) and it is really better than
> > > SRTM if you are outside USA. Hope you will enjoy the free meal.
> >
> >  I just had a look at the tiles near me, and there's quite a bit of
> > noise and obvious artefacts - unless there really is a 2000m tower
> > about 180m across that I've not noticed in the middle of the
> > countryside!
> >
> > I've not compared with SRTM yet...
> >
> > Barry
> >
> 
> I looked at some here around the North American Great Lakes, and I have to say
> I would be very leery about using it in low relief areas. Visually it looked a
> lot nicer in the California coastal range, so perhaps less vegetation and
> higher relief is important for the sensor.
> 
> That said, it's terrific that alternative global medium-resolution DEMs are
> becoming available. Also, I think this ASTER-derived product has captured
> higher latitude locations than SRTM (which gets to about 60N and 60S), so it
> may be not simply the best but the only choice for many regions.
> 
> Ashton
> 
> 
> --
> Ashton Shortridge
> Associate Professor			ashton at msu.edu
> Dept of Geography			http://www.msu.edu/~ashton
> 235 Geography Building		ph (517) 432-3561
> Michigan State University		fx (517) 432-1671
> 
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