stations were situated at a distance ranging from 
5 to 30 km. 
-28.60 — 
-28.80 — 
-29.00 — |} | UE Slik 
WGS84 J fi Th 7 TP 
Heights Li i | 
EXE E P m MIR 
-29.40 — 
  
  
-29.60 T ] T ] T 2 
80000.00 120000.00 160000.00 200000.00 
GPS time 
Fig.6 - Continuous vertical movement of GPS 
antenna located on Hells Gate floating platform 
under the effect of sea tidal undulation. 
Through the comparison of the profiles, it could 
be possible to detect the eventual displacements 
between floating and grounding ice along the 
trajectories. In figure 8 is presented the 
comparison between two profiles for a length of 
about two kilometres, as can noted the showed 
portion of the trajectory is probably referred to a 
floating condition since the altimetric 
differences between the two profiles made in 
maximum and minimum sea tidal undulation 
are of about the same order of sea tide 
amplitude (40 cm) in the same span of time. 
Another part of the experiment is reported in 
figure 9 and 10. In figure 9 the altimetric 
difference along the track, referred to a portion 
of other two continuous profiles made in an 
other area but in the same time of previous 
example is shown. In figure 10 the altimetric 
differences of homologous point of the profiles 
are reported. 
The difference is scattered but the mean value is 
centred around zero, so, considering the 
expected differences due to the sea tidal effect, 
it could be hypothized that the profile was 
probably made on grounding zone. 
34 
  
Fig.7- GPS antenna on the skidoo. 
Ellipsoidal Height (m) 
  
  
  
Fr ETT EE TE RT VI EER TT RET TTY TTT 
0 250 500 750 1000 1250 1500 1750 2000 
Distance (m) 
Fig. 8 - Comparison between two different GPS 
profiles made approximately in maximum and 
minimum sea tidal curve time. 
On the basis of the sea tidal undulation 
amplitude, with a maximum value of about 60 
cm, it was necessary to obtain the higher 
accuracy in order to compare the profiles. For 
the presence of high ionospheric disturbance, it 
was not possible to solve the whole profile and 
only the OTF algorithm permitted to recover 
partial portions. 
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B1. Vienna 1996 
-15 
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