The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences. Vol. XXXVII. Part B7. Beijing 2008 
To validate the results obtained, the ALOS PALSAR DInSAR 
results are compared against ground survey data for both mine 
sites. The DInSAR subsidence profile extracted from the 
ground survey points (Figure 7), compared with the ground 
survey data measured on 19 September 2007 and 12 November 
2007 at the Westcliff Mine, is shown in Figure 8. Figure 8 
shows that the DInSAR result matchs well with the ground 
survey data. The subsidence profile along point LOOl - L021 
has an RMSE of 0.6cm. The result suggests that this DInSAR 
technique has the capability to deliver sub-centimetre accuracy. 
Figure 9 shows the DInSAR height change result from ALOS 
images acquired on 27 Dec 2006 and 11 Feb 2007 and overlaid 
on Appin Mine plan and ground survey points (N042-N142). In 
order to assess the quality of the DInSAR result it is important 
to have good spatial and temporal overlap between the DInSAR 
result and the ground survey data. Unfortunately the difference 
between the date of the ground survey and the two ALOS 
PALSAR image acquisitions is quite significant in the case of 
Appin. The closest ground survey dates before and after the two 
acquisitions are in 19 Oct 2006 and 15 Jan 2007 for ALOS 
images 27 Dec 2006 and 06 Feb 2007 and 20 Feb 2007 for 
ALOS images 11 Feb 2007. In order to compare the ground 
survey data with DInSAR result, the deformation is assumed to 
change linearly between the ground survey dates before and 
after each ALOS acquisitions. The estimated height at 27 Dec 
2006 (estimated from 19 Oct 2006 and 15 Jan 2007) is then 
subtracted from the estimated height at 11 Feb 2007 (estimated 
from 06 Feb 2007 and 20 Feb 2007) and the comparison to the 
DInSAR result is shown in Figure 10. It can be seen that the 
DInSAR result and the ground survey data agree well with most 
survey points, including the area with the highest rate of 
subsidence. However, most of the error has been found from 
survey point number N80-N105, which is at the east of the 
subsidence bowl. Up to 4cm difference has been observed from 
point N80-N84. Apart from these points, the DInSAR result 
follows the ground truth very well and an RMSE of 1.7cm has 
been calculated. 
Figure 7. DInSAR height change derived from ascending ALOS 
images acquired on 29 Sep 2007 and 14 Nov 2007 (46 days 
apart) and overlaid on Westcliff Mine plan. 
Figure 8. Validation of DInSAR-derived subsidence profiles 
against ground truth. 
It is interesting to note that the subsidence bowl from the 
displacement maps derived from ascending (Figure 6e) and 
descending (Figure 6f) pairs are slightly different. For the 
ascending pairs (Figure 6a-e), the subsidence bowl seems to 
have higher subsidence in the west, whereas the subsidence 
bowl seems to have higher subsidence in the east for the 
descending pair (Figure 6f). This maybe caused by different 
displacements vector and incidence angle between two tracks. 
This may explain why the most of the error has been found on 
the east of the subsidence bowl. 
The RMSE 0.6cm and 1.7cm between the DInSAR-derived 
results and ground survey data have been observed in the two 
sites. The inconsistency between the ground survey data and the 
DInSAR result can be due to several reasons: (1) difference 
between the date of survey and the date of satellite image 
acquisitions, (2) the uncertainties in the georeferencing, (3) 
errors in the DInSAR processing, and (4) errors in the ground 
surveys. 
Figure 9. DInSAR height change derived from ascending ALOS 
images acquired on 27 Dec 2006 and 11 Feb 2007 (46 days 
apart) and overlaid on Appin Mine plan.