ul 2004 International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B7. Istanbul 2004
f errors. 32 Digital Terrain Model
e on the >
a good Outside the glaciers, the SRTM DEM (1200 pts / degree)
has been used. Such a DEM is already available for free
everywhere on earth, or will be very soon. Its quality is
mblance sufficient for the global image bundle block adjustment.
rocesses
podized On the glaciers themselves, the SRTM DEM has been
iometric improved by using the 2" and 3' SPOTS THR images,
veen the which, with a 31? incidence angle difference, and a time eb
different interval of 4 days, were the most favorable images for DEM 45.9E FEE 5E
val, one computation. :
d at the
lead to
3.3 Results
ntainous
side the After the first step of the method, the bundle block 45.8E E
glaciers adjustment, displacement image exhibits only very small M
image. residuals outside the glaciers (Figure 4). Note that the results
glacier are very similar with or without GCPs. We have computed
*st slope the residual errors outside the glaciers, using GCPs, and they
one, can happened to be of the order of 0.5m (rms). Figures 3 and 4
show how system level bundle block adjustment improves B ida
the global image quality, hence the measurement accuracy of
> olacie
ifie glaciers motion. Figure 4: Offsets in longitude, obtained after secondary
MONS image resampling and bundle block adjustment
^ [E 7 E
ed for a 5100000 rr
glaciers sn um : = : :
EE". 2822 ln From the geocoded motion maps (F igure 4 and its equivalent
2 good put. in latitude), we can extract the profiles passing through the
t GPS probes, and check the consistency with the motion
nen has 5090000 derived from the ground measurements. Of course, we take
; SPOTS into account the time interval between the D-GPS
fore be measurements, and keep the same scale when comparing all
Ey. measurements (for example we express all in cm/day).
5000000 Figure 5 shows a detail, over the glaciers, of the total
on this horizontal displacement map, from 23 August to 18
0 pairs: September. This map is easily deduced from the two
computed maps, in latitude and in longitude. Black dots
d -15.2°, 5070000
es Suse represent the GPS measurements, and the black line the line
: of interest. The work of comparison between the
measurements in still on-going, but seems very promising,
showing a good consistency between motion computed from
the SPOTS images and motion computed from the D-GPS
measurements.
on angle: 330000 340000 350000
5 0-43-39-20-1. 0:04 52 «3
Figure 3: Offsets in longitude, no resampling, direct geo-
coding without bundle block adjustment Next work will consist into comparing the results obtained
independently from the two image pairs. It is assumed that
the glaciers surface velocity is rather stable. The first pair
being less favorable for the acquisition conditions (different
incidence angles), we will be able to measure the impact of
such conditions on the results.
detail,
ction.
833
