GAVB
12618S001
IDS GAVB
data should not be used. Not enough data
GAVB not in
ITRF2005
GAVB
velocity in ITRF2005 velocity field (EURA) is -17.20 19.07 11.44
GAVB
velocity in ITRF2005 as computed from GPS data (1 year) is (in NEU) -23.86 2.97
-4.51, so we obtain 7.85 6.77 -22.16 (in XYZ). These 2 velocities are rather
different, so we need to test these 2 hypothesis toward a GPS position
expressed in 2007.5
Preliminary
computations:
Hyp 1:
using orignal ITRF2005 coordinates
Using the
most recent DORIS weekly solutions (ign07d02) and fixing the velocity to
ITRF2005, we obtain :
2007.5 GAVB
4783636.5096 2140697.6588 3623255.2870 -17.20 19.07 11.44
statistics
GAVB XYZ 0.0036 0.0017 0.0032 131
Local tie
with GPS (PGVB = GVD0)
PGVB GAVB
0.192 -14.351 9.009
So GPS
coordinates (derived from DORIS results and using original ITRF2005 velocity
would give)
2007.5 GVD0
4783636.3176 2140712.0098 3623246.2780 -17.20 19.07 11.44
Hyp. 2:
using ITRF2005 velocities provided by Erricos Pavlis and expressed in ITRF2005
Using the
most recent DORIS weekly solutions (ign07d02) and fixing the velocity to
ITRF2005 as derived from 1 year of GPS data, we obtain
2007.5 GAVB
4783636.5443 2140697.6426 3623255.2428 7.85 6.77 -22.16
statistics
GAVB XYZ 0.0010 0.0012 0.0019 131
We can see
that the statistics are 3 times better than before (using original ITRF2005
velocity). This means that the velocity observed by DORIS is more consistent to
the GPS velocity than to the ITRF2005 velocity field.
This can
also be seend from the DORIS velocity estimates. Ign07d02 (position/velocity
computed over the whole range of DORIS data provides): 7.12 11.89 -10.17, which
is closer to the GPS-velocity estimation but quite different from ITRF2005
velocity field. This may be expected due to the complex geodynamics of the
Mediterranea.
Using the
geodetic local tie (GPS/DORIS), we can also compute GPS coordinates derived
from DORIS data, using these velocities. We then obtain:
2007.5 GVD0
4783636.352 2140711.9936 3623246.2338 7.85 6.77 -22.16
statistics
GVD0 XYZ 0.0010 0.0012 0.0019 131
Results
provided by Erricos Pavlis are (in ITRF2005), the epoch of observation is
2007.5 (based on 1 year of GPS observations)
GVD0 @
2007.5
4783636.3608
±0.0007
2140712.018
±0.0005
3623246.2188
±0.0005
It is clear
that Hyp 2 is much closer to the GPS results than Hyp. 1
We would
then recommend using the DORIS coordinates derived from the DORIS data, using
the GPS velocity (expressed in ITRF2005), using 1 year of data. We then obtain
2007.5 GAVB
4783636.5443 2140697.6426 3623255.2428 7.85 6.77 -22.16
so when
extrapolating at epoch 2000.0, we have :
2000.0 GAVB
4783636.4855 2140697.5918 3623255.4090 7.85 6.77 -22.16
According to the digital model of plate
boundaries PB2002 proposed by Bird (2003), Gavdos, like Dionysos, is located on
the Aegean Sea micro-plate. This model, which also proposes rotation velocity
vectors of 14 plates and 38 micro-plates, gives the following velocity for
GAVB: 4.39 9.52 -11.42 mm/yr (using NNR-N1A PCFC
pole as PCFC is fixed in PB2002).
This is why
it was not correct to use the ITRF2005 velocity field, assuming that GAVB was
on the European plate.
Recommendation:
2000.0 GAVB
4783636.486 2140697.592 3623255.409 7.85 6.77 -22.16