SRTM Files

[ElMazagangy]

I found links for SRTM files

http://dds.cr.usgs.gov/srtm/version1/
http://dds.cr.usgs.gov/srtm/version2_1/

but I don't know the difference between version 1 and 2 and SRTM1, SRTM3, SRTM30

IF any one know the difference please advice.

[ElMazagangy]

I found this whaich can explain the above thread:


Version 1 of the SRTM data consists of the original Digital Elevation Models produced
by the SRTM project with data from the STS-99 mission in Feb., 2000, and delivered to
the National Geospatial-Intelligence Agency (NGA.) These data are unedited and
contain spurious data points in area of low radar backscatter such as water bodies.

Version 2 was the results of a substantial editing effort by the NGA and exhibited well
defined water bodies and coastlines and the absence of spikes and wells (single pixel
errors), although some areas of missing data (ʻvoidsʼ) were still present. The Version 2
directory also contains the vectorized coastline mask used by NGA in the editing, called
SRTM Water Body Data (SWBD), in shapefile format.

Version 2.1 is a recalculation of the SRTM3 (nominal 90 meter sample spacing) version
made by 3x3 averaging of the full resolution edited data. Version 2 had been generated
by masking in edited samples from the lower-resolution publicly released by the NGA,
and contained occasional artifacts, and in particular a slight vertical “banding” in data
beyond 50° latitude. These have been eliminated in Version 2.1

[byja]

To start with, SRTM1, SRTM3 and SRTM30 are digital elevation models (DEMs) with 1 arcsecond, 3 arcseconds and 30 arcseconds resolution. Unless you're from US or Canada, where SRTM1 is available, SRTM3 is the most interesting DEM, cause of the resolution (~90m).
v2 data was reprocessed v1 data, which was rather raw. And it had some corrections such as zero-fills (open up any v1 file in DEM viewer and you'd see black spots), coastline correction (coastline in v1 is completely messed-up, you don't know where land ends and sea begins), and also sea level cleanup (same problem on the other side).