International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Volume XXXIX-B7, 2012
XXII ISPRS Congress, 25 August — 01 September 2012, Melbourne, Australia
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Figure 8: Difference between TanDEM-X and ICESat on
amplitude mosaick, tile N39W79, range of values [-3; 3]
TanDEM-SRTM Yet ape 13 12.47 M23
T A tuus
Figure 9: Difference between TanDEM-X and SRTM-C,
tile N39W79, range of values [-20; 20]
Differences-Between-Meighbors EEE
Figure 10: Difference between neighboring acquisitions,
tile N39W79, range of values [0; 6]
48
4. ADDITIONAL PRODUCT LAYERS
Along with the digital elevation model, which is the main
product of the TanDEM-X mission, additional information
layers will be available. These additional layers are congruent
with the DEM and have the same nominal spacing of 0.4
arcseconds. As mentioned above, the products are delivered in
1°x1° tiles and comprise the following layers:
Height Error Map — HEM:
The values represent the random height error for each DEM
pixel in form of the standard deviation. The value is derived
from the interferometric coherence and geometrical
consideration and thus represents the result of rigorous error
propagation.
Layover and Shadow Mask — LSM:
The values represent flags where layover and shadow areas are
identified. The shadow information is based on (SRTM-C and
GLOBE) and will therefore only be a rough estimate for many
regions. The layover is based on the TanDEM-X DEM.
Void Mask — VOM:
The values represent flags where larger height inconsistencies,
like differences above a predefined threshold (e.g. 10m)
between different DEM acquisitions occur. These pixels should
be masked out in the elevation model in order to obtain a more
reliable DEM.
Water Indication Mask — WAM:
The values represent flags where water bodies are identified
during processing. Water is identified by three different
extraction methods:
- with a strong amplitude threshold, normally < 40 digital
number (DN)
- with a more relaxed amplitude threshold, normally < 60 DN
- with a coherence threshold, normally < 0.23
The number of occurrences reflects the number of single
acquisitions fulfilling the respective threshold. The maximum
number of annotated occurrences for each method is three.
Interpolation Mask — [PM:
The values indicate pixel where small spikes and wells were
interpolated.
Coverage Mask — COV:
The values indicate the number of acquisitions contributing a
valid DEM pixel to the elevation model.
Amplitude Mosaick - AMP:
The values represent the mosaic of the geocoded SAR
amplitude images corresponding to the active channel of the
DEM acquisitions.
Detailed information about the TanDEM-X product (DEM and
additional layers) can be found in the “TanDEM-X DEM
Product Specification" (TanDEM-X Ground Segment 2011).
In the following a subset of approximately 8km x 8km was
extracted in full 0.4 x 0.4 arcsecond resolution 30 km east of
Jacksonville, North Carolina from the tile N34W78 (center of
subset — 34?46"N, 77?9"W). The result of the WAM extraction
is exemplarily depicted for tis subset. The amplitude image
shows a river expanding towards its water mouth into the
Atlantic (Figure 11). The corresponding height values in the
DEM appear noisy as interferometric data sets have generally
low coherence over water (Figure 12). On the over hand details
like the clear-cut for the railroad route running from east to west
are clearly visible (slightly left of the center).
Figure 13 shows the Height Error Map where bright values
indicate larger height error and lower coherence, respectively.
