The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences. Vol. XXXVII. Part Bl. Beijing 2008 
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4.3 Planned Test Program and Current Status 
The intent is to acquire data in several areas representing 
different forest conditions and topography. In all cases, 
ancillary data are required as part of the validation exercise. 
Selection of the test sites is based upon the availability and 
quality of the following data sets: 
• Lidar ground data for validation of the PolInSAR- 
derived bare-earth DEM, 
• X-band data from previous STAR-3/ or TopoSAR 
campaigns will be used for corroboration of tree 
height, 
• Reports on species, tree heights, stem density, DBH, 
etc as available from public or private sources 
Preliminary tests have occurred, enabling engineering issues to 
be addressed and mitigated. SNR at the 25db level has been 
confirmed for VV and HH in bare areas. Polarimetric 
calibration has led to cross-talk less than -25 db which is 
deemed adequate. Polarization imbalances have been corrected 
to the 5%/5 degree level (amplitude/phase). 
4.4 Preliminary results 
Some preliminary results have been obtained from one of the 
datasets acquired recently. The test site is in a heavily forested 
region containing a pattern of alternate forest and clearcut areas. 
The forest in this area is mainly composed of pine trees with 
height ranging from 10-25m and with relatively homogeneous 
growth in the forested patches. Figure 7 shows a ground photo 
looking towards the forest. The forest in this location is quite 
dense, with estimated tree heights about 20m on average. A 
bare-earth DEM was available for truth (30 cm accuracy quoted 
by Terrapoint, the supplier). Also, an X-Band DSM from the 
TopoSAR system flown in 2006 (prior to the L-Band 
configuration change) was available to provide an under 
estimated reference of the canopy height. 
process within the forest patches however, reflects the ground 
elevation over most of the test area. 
In Figure 8 we show the result of merging the two results such 
as to preserve elevation continuity across the forest boundary. 
The blue line shows the merged elevation profile representing 
the terrain while the green line and the red lines are the 
approximate canopy and bare-earth elevations from X-Band and 
lidar respectively. The merged L-Band DEM remains within 5 
meters of the ‘truth’ within the 15-20 meter forest. However it 
fails in the sloped region where canopy heights are reduced. 
This is possibly because the model is not optimized for trees in 
this height range. This issue is to be addressed. 
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Cross Section 
Figure 7. Ground photo during L-Band data acquisition 
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The coherence (magnitude) optimization and coherence region 
algorithms have been applied to the calibrated dataset. The 
elevation derived from the optimized coherence magnitude 
follows the terrain quite well on the bare/new growth areas but 
inside the forest canopy appears to be similar to the X-Band 
DSM height. The elevation derived from the phase optimization 
Figure 8. Top: Elevation cross-profile of lidar bald-earth (Red), 
X-Band DSM (data acquired in April 2006, Green), L-Band 
ground elevation (blue). Bottom: Location of the profile line is 
overlaid on a color airphoto. 
5. SUMMARY AND CONCLUSIONS 
The NEXTMap" program, based upon airborne X-Band HH 
InSAR, is in the process of creating a 3-dimensional, 
homogeneous, seamless database including DSM, DTM and 
ORI products, for eighteen countries of Western Europe and for 
the USA (excluding Alaska). The DSM is specified at 1 m 
RMSE vertical accuracy for 5 m sample spacing, while the ORI 
is specified at 1.25m resolution with better than 2 m RMSE 
horizontal accuracy. For many applications the combination of 
detail provided, national and super-national availability and 
shared pricing through license arrangements should produce an 
attractive user opportunity. The creation of the product datasets 
for both areas is well underway and scheduled for completion, 
in the case of Western Europe, for late 2008 and about 1 year 
later for the USA. With respect to many market applications 
such as visualization, flood risk, and auto safety these products 
should occupy a solid niche, relative to alternative technologies.