FA | 
AS 
  
between the single-pass InSAR and multi-pass InSAR with 
increasing incidence angle. When all data from the three sites 
were combined (Table 4), Single-pass h,„. was more similar to 
NEXTMap data in the FR. The number of void samples 
(missing data due to decorrelation in InSAR phase) were less 
than 3% of the single-pass data sampled. An increase in void 
data samples is expected with spaceborne X-HH InSAR such as 
that derived from Tandem-X because there is a time lag 
between the TerraSAR and Tandem-X data. 
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 
  
  
  
  
  
  
  
  
  
  
  
  
# ; Mean 
0 : : . | transect * ved RMSD Difference | &? 
ss samples pos (m) 
NR 11 5557 148 2.61 -0.18 | 0.82 
MR 9 7144 207 2.01 -0.36 | 0.86 
FR 6 6860 185 132 -0.39 | 0.97 
  
Table 4. Comparison of hg, for 19,561 sample points located 
along transect lines of slopes «10 in the NR (0 =35), MR (0 
=45"), and FR (0 =55), for single-pass X-HH InSAR (single- 
data takes) compared to NEXTMap X-HH InSAR (multi-pass) 
for all data combined, and averaged based on samples per site. 
Given the difference in site characteristics, analysis were 
conducted per site (Tables 5-7), to determine if similar results 
prevailed. 
  
  
  
  
  
  
  
  
  
  
  
Angle oh A d RMSD rm Rm 
samples data ce (m) 
NR 2 1656 37 4.01 -0.77 | 0.81 
MR 3 1416 93 297 -0.48 | 0.71 
FR 2 1973 81 0.96 -0.58 | 0.99 
  
  
Table 5. Comparison of hg, for 5,045 sample points located 
along transect lines of slopes <10 across all three incidence 
angles for the Ely site, generated from single-pass X-HH InSAR 
compared to NEXTMap X-HH InSAR (multi-pass). 
  
  
  
# # Mean 
Angle We $ transect void RMSD Differen R 
P samples data ce (m) 
NR 1 323 11 1.65 -0.25 | 0.51 
MR 2 1973 81 0.96 -0.58 | 0.99 
  
  
  
  
  
  
  
  
  
Table 6. Comparison of h, for 2,296 sample points located 
along transect lines of slopes «10 across NR and MR incidence 
angles (FR data were not available) for the International Falls 
site, generated from single-pass X-HH InSAR compared to 
NEXTMap X-HH InSAR (multi-pass). 
  
  
  
  
  
  
  
  
  
  
  
# # Mean 
Angle : ^ , | transect | void RMSD Differen | & 
Strips samples data ce (m) 
NR 6 2640 81 1.04 -0.03 | 0.96 
MR 3 4484 89 1.15 -0.03 | 0.99 
FR 3 4484 89 1.27 -0.23 0.99 
  
  
Table 7. Comparison of h, for 11.608 sample points located 
along transect lines of slopes <10 across all three incidence 
angles for the Arizona site, generated from single-pass X-HH 
InSAR compared to NEXTMap X-HH InSAR (multi-pass). 
The mean differences shown in Tables 5-7 are all negative as in 
Table 4, meaning that on average, single-pass X-HH hg, was 
slightly lower than NEXTMap h,,. However, the effect of 
incidence angle on RMSD and R? was site-dependent. The trend 
of an increase in agreement (decrease in mean difference) 
between single- and multi-pass data from NR to MR to FR, as 
presented in Table 4, was not found at all sites. In the case of 
the Arizona site, the differences increase slightly from NR to 
MR to FR. At the International Falls site, where only NR and 
MR data were available, the NR single-pass X-HH hg, data 
were more similar to the multi-pass data than were the MR data. 
These results were unexpected. Could this mean that X-HH 
InSAR derived h,, is sometimes closer to multi-pass data 
averaged data in the NR and sometimes closer in the FR? 
Additional information about how the multi-pass data were put 
together is needed to make this conclusion. One possibility 
could be that slight twisting along a single flight line (Figure 6) 
can occur due to the long flight lines of NEXTMap (up to 1,200 
km long) and also place a role. Another is that it may be 
possible that at one site the multi-pass data stitched together NR 
or FR data in the same area, producing a multi-pass image that 
still shows a range effect. In other sites it is possible that the 
multi-pass data averages NR and FR data of the same pixels 
from different single-data take images. 
  
  
  
  
  
  
  
  
  
  
  
  
  
Vu NR WFR Location Along Transect Line (m) 
  
Figure 6. Three examples of X-HH airborne flight line twisting. 
The top graph illustrates a strong correlation between the NR 
(dashed line) and FR (solid line) for two flight line strips (that 
have been controlled using ground control) over the same 
transect line. The middle and bottom graphs for a transect line 
located both in the NR and FR do not correlate well. In the 
middle graph, the beginning of the transect (left side of the 
graph, starting at number 1 does not compare well in NR and 
FR, but they begin to converge at about data point #81 
approximately 54 km from the start of data collection for the 
NR pass and at 104 km for the FR pass. The bottom graph 
shows a strong correlation between NR and FR profiles along 
the same transect line at the beginning, but they begin to 
separate from each other at about data point #169 
approximately, 68 km from the start of data collection for the 
NR line (pass #1) and at 134 km for the blue line (pass #2). 
7. CONCLUSIONS 
This paper assessed the impact of incidence angle on X-HH 
interferometric Synthetic Aperture Radar (InSAR) single- and