tl 2004 International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B2. Istanbul 2004 
ind 4. THE USE OF P-BAND IFSAR FOR OBTAINING polarimetric response. In this work, the polarization bases 
has BARE-EARTH DEMS BENEATH FOREST CANOPY were optimized according te an internally developed coherence 
optimization scheme and the assumption was made that the 
The use of long-wavelength IFSAR has been posited for many optimum coherence corresponds to the polarization state 
the years as a possible means of obtaining bare-earth DEMs associated with the ground return. This makes the results 
cy through forest canopy. Long-wavelength in this context usually somewhat model independent (apart from the stated 
by means L-Band or P-Band. As interest has grown, theoretical assumption). 
ata advances have perhaps outstripped experimental demonstration 
‘as however. Among the major research centers working in this The delivered results included an X-Band DSM and a P-Band 
fic area, DLR and various collaborators have demonstrated the use DSM and DTM as well as various strip products and ancillary 
in of fully-polarized L-Band repeat-pass IFSAR in forests in information. The data were processed and delivered to the 
od Scotland and Germany. The relatively new GeoSAR system client without the benefit of the fore-mentioned ground control 
ag has single-pass P-Band capability and results are expected to be (apart from four control points in cleared areas). However it 
ta published imminently. In this paper we wish to summarize was possible to perform a sanity check of the products by 
Id results that were first presented by Mercer, et. al. (2003b). comparing X and P-Band profiles in transition areas from bare 
IS to forest (Figure 8). This profile shows the X-Band following 
is The ‘Capitol Forest’ project, utilized the X-Band and P-Band the forest canopy (it actually underestimates the tree tops by 
of capabilities of the TopoSAR system (Figure 2 and Table 1). several meters (Andersen, et. al. (2003)), and beneath it the P- 
Or The project area is a 5.2 kmsq forestry research test site in Band DSM and DTM. In this instance the DTM only differs 
in Washington State, USA, was funded by the Makah Tribe, and from the DSM in that it has been smoothed. It appears that the 
has been extensively ground-truthed by members of a forestry 
research consortium which includes the University of 
Washington and the Forestry Research Center of the USDA 
(Andersen, et al. 2003). ‚The truth includes: 290 ground survey 
points, located beneath the canopy, as well as others in cleared 
areas; lidar data from a helicopter-borne SAAB TopEye system 
providing 4 points/msq; and aerial color photography at various 
scales (1:12,000, 1,7000 and selected stereo at 1:3,000). The 
site has a range of forest conditions and terrain conditions. The 
forest is mainly Douglas-fir and western hemlock. One of the 
stands is mature 70-year unthinned growth with a stand density 
of 280 stems/hectare and tree heights exceeding 40 meters. 
Other stands are younger and have been thinned to varying 
degrees. Additionally there are areas of clearcut. A color 
ortho-photo shows the area along with the locations of the 
ground survey points (Figure 7). 
  
   
   
  
Figure 7. Ortho-photo of test area. Coloured points show the 
location of the ground survey points. Color-coding 
differentiates degrees of thinning in the various stands (e.g. 
white indicates no thinning, and yellow is lightly thinned. 
The terrain has very challenging slopes, from flat up to 45 
degrees. The area was flown in September 2002 by TopoSAR. 
The coverage included two opposite looks of X-Band data and 
four orthogonal looks of P-Band acquisition. Two IFSAR 
baselines were acquired for comparative purposes (50 meters 
and 83 meters). The 83 meter results were superior and are 
presented here. Importantly, P-Band data were acquired in fully 
polarimetric mode (HH, VV, HV and VH). The relevance of 
this remark is that while long-wavelength signals do penetrate 
to the ground, the interferometric response is from the whole of 
the canopy; the idea is that the response from different parts of 
canopy/ground system can be differentiated by their 
P-Band is sampling ground as it makes the transition from bare 
to forest and back. In Table 4 we present the results upon 
comparing the P-Band DTM with the ground survey points. 
The slopes were moderate at the locations of these points. 
  
  
  
  
  
  
  
   
   
  
  
  
0 100 200 300 400° 500 600 700 800 
Meters 
  
  
  
Figure 8. Top: Air photo with location of profile overlaid. 
Bottom: Elevation profile showing X-Band DSM (dark green), 
P-Band DSM (red) and P-Band DTM (light green). (X-P) 
differences as much as 40 meters may be observed. 
of Forest Thin 
-GCPs Clear Cut ht Un-Cut 
Mean -0.5 -0.4 -0.2 0.4|meters 
Std Dev'n 1.2 1 2. 3.3[meters 
RMSE 1; 1.1 2.3 3.3|meters 
n 21 148 121 
Table 4. Statistics of (P-Band DTM — ground survey points) for 
varying degrees of forest density. In the mature growth uncut 
845