pass derived hy, along transect lines were considered as 
reference data; i.e. this is not an accuracy assessment. The R? 
values were also tabulated. The results for all site data 
combined were tabulated as a weighted average based on the 
number of samples per site, since they were not equal at each 
site. 
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 
  
Wetland 8 NR 3.11 | -146 | 4.11 -2.96 
  
  
  
  
  
  
  
  
(7.2 m) 7 MR 3.01 | -1.35 3.99 -2.19 
  
  
Table 2. NEXTMap and single-data take X-HH InSAR-derived 
hg, error assessment against in situ vegetation canopy height for 
the International Falls site, stratified by vegetation cover type 
and incidence angle range for «10 terrain slope. 
  
S s km - Far-Range (FR) 
   
Akm - Mid-Range (MR) 
| km - Near-Range (NR) 
  
  
  
Figure 5. Transect line (dashed line) positions in near-, mid-, 
and far-range for one strip of X-HH InSAR data. 
6. RESULTS AND DISCUSSION 
6.1 Vertical Accuracy of IDSAR Vegetation Canopy Height 
The results of the incidence angle analysis comparing the X-HH 
InSAR single- and multi-pass he data against in situ 
measurements of vegetation canopy height in flat terrain (<10") 
stratified by vegetation class and incidence angle are presented 
in Tables 1-3 for all site data stratified by research site, 
vegetation type, and incidence angle class (NR, MR, FR). 
X-HH InSAR | X-HH InSAR 
  
  
  
  
  
  
  
  
  
  
  
  
  
Vegetation # NEXTMap single-pass 
(mean tree in 0 mean mean 
height) situ rmse | error | rmse | error 
(m) (m) (m) (m) 
Shrub 154 | NR 1.77 | -075 2.18 -2.48 
(43 m) 184 | MR 1.71 | -0.73 2.11 -2.40 
139 | FR 1.744 074 | 215 -2.44 
Decidhons 19 | NR 6.25 | -2.45 6.84 -3.18 
(15.2 m) 21 | MR 6.08 | -2.37 6.63 -3.08 
18 | FR 6.15 | -2.41 6.74 -3.13 
Cénitétons 29 | NR 6.23 | -281 8.34 -2.06 
(15.5 m) 31 | MR 6.04 | -2.72 8.08 -2.00 
27 | FR 6.13} -2.77 8.21 -2.03 
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
X-HH InSAR X-HH InSAR 
Vegetation # NEXTMap Single-pass 
(mean tree in 0 mean mean 
height) situ nnse | error | rmse error 
(m) (m) (m) (m) 
Shrub 9 NR 1.92 | -0.69 2.89 -2.31 
(4.1 m) 6 MR 1.89 | -0.54 2.99 -2.52 
5 FR 1.91 | -0.63 2.74 -2.99 
S 24 | NR 6.24 | -2.43 7.32 -3.48 
Da 31 [MR ( 6111 251 7001 324 
49 | FR 6.31 | -2.11 7.17 -3.29 
" : 22 I NR 6.29 | -2.83 8.48 -2.73 
C ES 31 IMRI 627] 299] 799] 23 
29 | FR 6.12] -2.18 8.41 -2.99 
Mixed 6 NR 6.42 | -221 7.21 -3.05 
(14.7 m) 9 MR 6.32 | -2.43 7.33 -3.25 
S FR 6.33 | -2.19 7.45 -3.19 
  
  
  
  
  
  
  
  
Table 1. NEXTMap and single-data take X-HH InSAR-derived 
hy, error assessment against in situ vegetation canopy height for 
the Ely site, stratified by vegetation cover type and incidence 
angle range for «10 terrain slope. 
  
  
  
  
  
  
  
  
  
  
  
  
  
  
X-HH InSAR X-HH InSAR 
Vegetation # NEXTMap single-pass 
(mean tree in 0 mean mean 
height) situ rmse | error | rmse error 
(m) (m) (m) (m) 
Shrub 10 | NR 1.86 | -0.83 2.29 -2.01 
(4.0 m) 8 MR 1.68 | -0.71 2.33 -2.21 
Deciduous 27 4 NR 6.44 | -2.15 8.12 -3.12 
(15.1 m) 29 | MR 6,1 | -2.34 8.01 -2.97 
Coniferous 15 | NR 6.35 | -2.93 9.02 -2.22 
(15:5 m) 15 | MR 6.24 | -2.77 8.89 -2.11 
Mixed 14 | NR 6.52 | -2.26 7.06 -3.38 
(14.6 m) 16 | MR 6.12] -2.13 7.26 -2.87 
  
  
  
  
  
Table 3. NEXTMap and single-data take X-HH InSAR-derived 
hy, error assessment against in situ vegetation canopy height for 
the Arizona site, stratified by vegetation cover type and 
incidence angle range for «10 terrain slope. 
The results for the multi-pass INSAR (NEXTMap), in most 
cases, supported the theory that in NR (steep incidence angles, 
e.g. © = 35") greater exposure of the lower vegetation canopy 
structure leads to greater canopy penetration, greater volume 
scattering if there is understory, or if little to no understory, 
greater double bounce, and a decrease in the amount of volume 
scattering contributions higher up in the canopy. This scenario 
results in a lower overall scattering phase centre height (hy) or 
greater vegetation canopy height underestimation in the single- 
data take InSAR data. The opposite effect occurs in the FR, 
where at shallow incidence angles (0 = 55) there is an increase 
in more relative volume scattering from the upper canopy, little 
to no ground scattering contributions, resulting in more accurate 
vegetation canopy height estimates. The improvements from 
NR to FR were, however, minor, indicating that the multi-pass 
InSAR are not impacted by changes in incidence angle in flat 
terrain due to the aggregation of multiple flight line passes. In 
the case of the single-data take results, the theory did not hold 
through. In fact, in some cases the NR were better than the FR, 
and in most cases the MR were worse than both the NR and FR. 
Overall, however, the differences were not significant, 
indicating that that incidence angle range for flat terrain does 
not play a major role in the vegetation canopy height accuracy. 
Comparisons of the transect lines (Figure 5) are presented in the 
next section and help to explain a possible reason for the 
deviation from the expected theory. 
6.2 Single and Multi-Pass X-HH InSAR Scattering Phase 
Centre Height Comparison — Stratified by Incidence Angle 
The results of the incidence angle analysis comparing transect 
lines that run parallel to the X-HH InSAR single-data take flight 
line strips (Figure 5) against the NEXTMap multi-pass X-HH 
InSAR in flat terrain («10») are presented in Table 4 for all site 
data combined and stratified by range class into NR, MR, and 
FR, respectively. The mean differences shown in Table 4 are all 
negative, meaning that on average, single-data take derived hy, 
was slightly lower than NEXTMap h,pe The RMSD decreased 
and R° increased from NR to FR, indicating a greater correlation