Figure 5. Differences in LOS-change detected by ALOS2 and Sentinel-1
seasonal interferograms (Figures 4a-d and 4f-i). In the last term of
seasonal analysis (Figure 4e and 4j), we could not estimate differences
due to coherence loss.
Figure 5 shows the differences between ALOS2 and Sentinel-1 InSAR data
with nearly identical periods, which may help in cross-validating the
measurements and understanding the actual deformation processes. The
estimated differences and their 2σ scatter were 0.5±1.2cm (Fig
5a),0.7±2.3cm (Fig 5b),0.3±1.3cm (Fig 5c), and 0.6±0.3cm (Fig 5d), with
mean of 0.5±1.5 cm. The differences and their variances were variable
over time but apparently indicated some systematic trends. For instance,
over the east-facing slopes, the differences were almost always positive
(This is discussed more comprehensively in section 5.1).
The Sentinel-1 interferograms for 2017 demonstrate that the progress of
deformation was not at a constant rate (Figure 6). The most rapid
deformation took place in June (periods 1 and 2) with no substantial
deformation in July (period 3) and started to subside again in August
(periods 4-6). We found that the subsidence occurred sporadically over
time and space and that the burned area did not uniformly subside. For
periods 4, 5 and 9 we were unable to perform phase unwrapping at
specific locations near the ridge and the boundaries between the burned
and unburned areas. These unwrapping errors were responsible for the
localized, large differences observed in Figure 5b. We confirmed the
presence of low coherence bands along the unwrapping errors, which may
suggest large phase jumps due to large displacements during the 12 days;
enigmatically, no such line-shaped low coherence was detected in the
long-term ALOS2 interferograms. Moreover, Figure 6 demonstrates that the
frost heave started in late September, which was missed in the periods
(b) and (g) of Figure 4, and that the absence of any deformation signals
lasted from early December to May of the following year. We will
physically interpret the absence of deformation signals during the
coldest season in section 5.3.