Products
Digital Elevation Model
The individual elevation values are generated
from signals reflected by an area on ground of an approximate size
of 25 x 25 m. The model is transformed into geographic coordinates
and is provided in tiles of 15' (arc-minute) size in latitude and
longitude. The product volume is about 3 Mbytes including the corresponding
height error map. This allows the fast provision via
the internet. The distribution format is DTED (Digital Terrain Elevation
Data). Either the ellipsoidal height according
to WGS84 or the Mean Sea Level can be selected as height reference
The product specification of the SRTM/X-SAR DEM
is listed in table 1.
Raster
size
|
1"x1"
Lat &Lon
|
Height
levels
|
1m
|
Datum
(horizontal)
|
WGS84
|
Datum
(vertikal)
|
WGS84
or MSL (optionally)
|
Data
format
|
16-bit
Signed Integer
|
horizontal
accuracy (absolute)
|
±20m
90% circular error
|
horizontal
accuracy (relative)
|
±15m
90% circular error
|
vertical
accuracy (absolute)
|
±16m
90% vertical error
|
vertical
accuracy (relative)
|
±6m
90% vertical error
|
Table 1:
DEM Product
The height error map provides a local measure of the achieved
accuracy. It is statistically determined from a neighborhood of
image cells mainly considering the phase and baseline stability.
Thus it describes the precision relative to the surrounding. The
determination of the absolute accuracy requires the consideration
of reference measures.
SAR
Image Products
The image products are available in three different
presentations and image geometries. These are
- Single Look Complex (SSC)
- Multi Look Ground Range (MGD)
- Geocoded Terrain Corrected (GTC)
The SSC provides for each pixel the real as well as the imaginary
value in the sensor specific slant range geometry. During the MGD
generation the intensity value for every image pixel is determined
and is transformed into ground range geometry. This means a homogenous
sampling over range (perpendicular to the flight direction). During
the interferometric processing the three dimensional position of every
pixel is determined. This enables an ortho-rectification and a transformation
into a map projection (UTM). These steps are performed for the GTC
product. All image products cover an area of approximately 150 km
in azimuth and 50 km in range. The delivery format is CEOS.
Table 2 comprises the specifications of the image products.
|
|
MGD
|
SSC
|
GTC
|
Projection
|
Ground Range
|
Slant
Range
|
UTM
|
Ellipsoid
|
GEM6
|
n.a.
|
WGS84
|
Image
data format
|
Amplitude
|
Komplex
|
Amplitude
|
Spatial
resolution :
|
|
|
25
m
|
Azimut
|
25m
|
8-12
m
|
|
Range
|
25m
|
17
m
|
|
Pixel
Spacing:
|
|
|
25
m
|
Azimut
|
12.5
m
|
13.32
m
|
|
Range
|
12.5
m
|
3.9-5,8
m
|
|
Abs.
position errors (s):
|
|
|
<
30 m
|
Azimut
|
3km
|
3km
|
|
Range
|
<4
km
|
<4
km
|
|
Table 2: SAR Image Products
Data Policy Issues
Usually the SRTM/X-SAR products are made available
without restrictions. Restrictions due to foreign affairs or security
reasons become effective by decision of DLR's board of directors.
|
|
|
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