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Figure 4: Effect of penetration depth on the interferometric phase
effective baseline length [m]
[rad].
systematic under-estimation of the glacier topography. The topo-
graphic height error is given by
Ar sin(0)
a Aa
Qpd (9)
Considering a typical baseline of Bz100 m a height error AA,
of up to 100 m might occure.
323 Improperly chosen temporal model An improperly cho-
sen temporal model may also introduce systematic errors. In
common dInSAR approaches the flow of a glacier is usually con-
sidered as constant in amplitude and direction for the complete
observation period. Errors due to violations of this simplified
flow model are analyzed based on simulated data sets. The topo-
graphy related phase is simulated based on a DEM of a test gla-
cier (Sonklar glacier, Hall-Island, Franz-Josef Land). The motion
part of the phase increases linearly with time and is derived from
Equation (6). The surface velocity field at time t = 0 is simulated
based on the known velocity field of the same test glacier. Tests
with varying acceleration rates showed that the resulting system-
atic errors are significant for all test scenarios and for both, topo-
graphy and motion. Increasing the number of data sets allows to
significantly reduce the topography error Ah, but motion errors
appear nearly unchanged.
4 VALIDATION
In this section the presented estimation method is validated based
on multi-temporal data sets of a test area in the high Russian arc-
tic. Hall Island is one of the largest islands of the Russian ar-
chipelago Franz-Josef Land. Approximately situated at 80°10’ N
and 58°05" E, its variety of topographical and glaciological forms
as well as drastic changes of its environment attracts the attention
of glaciologists. An impression of Hall Island is given in Figure
5. Approximately 90 96 of the island is covered by the so called
& e It Ai 3
Figure 5: KATE-200 image of Hall Island, Franz-Josef Land su-
perimposed by a coarse information about its coastline and gla-
cier margins taken from (Vinogradov and Psaryova, 1965).
Moscow Ice Dome whose ice masses flow into the sea along sev-
eral large outlet glaciers. Ice free areas appear mainly in the north
of Hall Island and on the two headlands in the south-east (hatched
1007
International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B3. Istanbul 2004
Number | Name | Area [kzn?] | Length [km] |
1 Sonklar 54.0 9.0
2 Nr. 2 23.2 5.3
3 Nr. 3 6.0 2.6
4 Nr. 4 13.3 4.5
3 Nr. 7 47.1 9.8
6 Nr. 8 67.0 6.1
7 Nr. 12 56.7 8.5
8 Nr. 16 23:1 7:7
9 Nr. 17 33.6 5.8
10 Moscow 504.7 30.0
Table 1: Information about the largest outlet glacier on Hall Is-
land according to (Vinogradov and Psaryova, 1965).
areas in Figure 5). Nearly 50 % of the shoreline is dominated by
the calving ice fronts of the large outlet glaciers. Some infor-
mation about the most important outlet glaciers on Hall Island is
included in Table 1. The numbers in the first column of Table 1
correspond to the numbering in Figure 5.
4.1 Data sets
During the tandem- and ice-phase mission of the ERS1/2 satellite
system several data sets were acquired over the area of interest.
6 ERS SAR SLC's recorded during the ERSI/2 tandem mission
were chosen for further processing. Meteorological data has been
included in the selection process to warrant comparable atmo-
spheric conditions for all observations. All images are acquired
in 1995 and cover the period from summer until winter of the
mentioned year. The properties of the data sets are shown in Ta-
ble 2. The interferometric processing of the complex SAR images
[Satellit [| Datum [ Flugricht. | Basislinie (|]) | Basislinie ( 1.)
desc -19m -S0m
desc 57m 129 m
desc -0m -43 m
Table 2: Properties of used SAR data.
has been accomplished with the Doris v3.6 software developed at
the Delft Institute for Earth-oriented Space Research of the Tech-
nical University Delft, NL. The Phase and coherency image of a
subset of the September interferogram that covers Hall Island, are
shown in Figure 6. Areas with large displacement related phase
components are marked with white frames. The framed regions
correspond to the catchment areas of the outlet glaciers Sonklar.
Nr. 7, Nr. 8, Nr. 12 and Nr. 17 (consult Table 1 and Figure 5). In
Cu
Figure 6: Phase image (a)) and coherency image (b)) of the
September interferogram of Hall Island. The baseline of the in-
terferogram is zz 50 m.
order to utilize the data for usage in the estimation process, some
preprocessing steps are necessary. The most important step is the
unwrapping of the initially ambiguous interferometric phase val-
ues. In addition the data sets are co-registered and phase ramps
originating from orbit errors are removed based on control point
information.
