AREA
42202S005
AREB
42202S006
ARFB
42202S007
JoG AREA
data should be deleted from 23-JUN-2001 to 20-NOV-2001 (end) due to postseimic
activity + break at 23-JUN-2001
IDS AREA
data should be deleted from 23-JUN-2001 to 20-NOV-2001 (end) due to postseimic
activity + break at 23-JUN-2001
ITRF AREA
break on 24-JUN-2001
PW AREA
break on 24-JUN-2001 is not required for DORIS as no AREA data are to be used
after this epoch. Beacon is later replaced by AREB
ITRF ARFB
discontinuity 21-NOV-2001
DM#458
ARFB new station since 02-AUG-2006
JR velocity
should be the same for the DORIS, GPS and Laser station at the same periods
PW ITRF2005
velocities are different as no constrain between techniques were applied in
ITRF2005, after the first discontinuity
PW GPS time series at JPL
suggest that the movement is linear for AREB after 01-JAN-2002. This is also
confirmed by SOPAC
GPS time series. AREB data from start (12-DEC-2001) to 01-JAN-2002 should
then be deleted. There is then no need for a discontinuity for AREB as no data
is kept before (during the relaxation phase)
Preliminary
computations:
ITRF2005
did not constrain GPS, DORIS, Laser velocity to be the same, except for the
first station (AREA). So estimated velocities are quite large and unusable for
POD purposes (they will generate large uncertainties very soon). Here is the
latest AREB coordinate in ITRF2005 (ARE2)
AREB 2000.0
1942803.431 -5804071.522 -1796922.038 -42.61 33.58 -32.56
The
DORIS-only solution (tf_070515a), only assuming that velocity from AREB and
ARFB is the same, gives:
AREB 2000.0
1942803.384 -5804071.422 -1796922.133 -38.25 -4.45 3.17
While (in
tf_070515a), ARFB is
ARFB 2000.0
1942803.536 -5804071.586 -1796922.146 -38.25 -4.45 3.17
SIMB gives
the following local ties
AREB
42202S006 AREA 42202S005 -7.061 -6.369 2.771 0.002
ARFB
42202S007 AREA 42202S005 -7.107 -6.233 2.814 0.002
So
ARFB
42202S007 AREB 42202S006 -0.046 0.136 0.043 0.002
The
tf_070515a vector provides: -0.152 0.164 0.013
So this is
not too close. It is possible that AREB and ARFB still have a different
velocity.
Further
investigation required, especially use of GPS or SLR results (velocities, local
ties)
Velocity
derived from DORIS data are (assuming AREB and ARFB have the same values for
the velocity)
AREA 14.96
6.77 20.14
AREB -33.31
1.11 -2.86
ARFB -33.31
1.11 -2.86
2000.0 AREA
1942796.7908 -5804077.7517 -1796919.0523 14.96 6.77 20.14
statistics
AREA XYZ 0.0025 0.0017 0.0014 404
2000.0 AREB
1942803.3800 -5804071.4305 -1796922.1389 -33.31 1.11 -2.86
statistics
AREB XYZ 0.0030 0.0022 0.0023 84
2000.0 ARFB
1942803.5168 -5804071.6042 -1796922.1452 -33.31 1.11 -2.86
statistics
ARFB XYZ 0.0024 0.0016 0.0015 74
geodetic
local tie is
AREB
42202S006 AREA 42202S005 -7.061 -6.369 2.771 0.002
ARFB
42202S007 AREA 42202S005 -7.107 -6.233 2.814 0.002
So we can
derive
ARFB
42202S007 AREB 42202S006 -0.046 0.136 0.043
The vector
derived from the DORIS-derived coordinates is
ARFB AREB
-0.137 0.174 0.006
So it s
rather different, but it may be compatible with the geodetic local (formal
error is 2 mm)
If I use
the DORIS resuts, forcing the AREB and the ARFB velocity to be the same and
adding the local tie vector (with a 3 mm formal error), I obtain
2000.0 AREB
1942803.323 -5804071.414 -1796922.152 -14.35 -4.77 1.95
and
2000.0 ARFB
1942803.382 -5804071.559 -1796922.183 -14.35 -4.77 1.95
the derived
vector between AREB and ARFB is
ARFB AREB
-0.059 0.145 0.031
Which is
compatible with the local tie from SIMB
We could
accept these coordinates
2000.0 AREB
1942803.323 -5804071.414 -1796922.152 -14.35 -4.77 1.95
and
2000.0 ARFB
1942803.382 -5804071.559 -1796922.183 -14.35 -4.77 1.95
and delete
all information between the Earthqualke and 2002.0
Final
computation:
GPS results
(JPL, Mike Heflin) are available on-line at the following URL (station AREQ)
http://sideshow.jpl.nasa.gov/mbh/all/AREQ.html
From this
plot, we can select 4 periods for this station :
Period 1 = until the Earhquake (23-JUN-2001)
A constant
velocity can describe the station displacement
In this
period of observation, only station AREA is present
The
estimated GPS velocity is (lat/lon/rad) 15.90 11.02 -0.10
So the
velocity in ITRF2005 (XYZ in mm) is 11.85 -0.68 15.27
By using
weekly DORIS solution (before 23-JUNE-2001) and fixing the velocity to the
above value derived from GPS, we obtain :
2000.0 AREA
1942796.7869 -5804077.7625 -1796919.0584 11.85 -0.68 15.27
statistics
AREA XYZ 0.0025 0.0018 0.0015 404
The
original ITRF2005 position and velocity was:
2000.0 AREA
1942796.793 -5804077.724 -1796919.043 14.14 2.37 15.42
so there is
a significant different in Y. We prefer to use our own-DORIS solution for this
station:
2000.0 AREA
1942796.789 -5804077.763 -1796919.058 11.85 -0.68 15.27
Period 2 = after the Earthquake and before
2002
The
displacement is not linear and DORIS data should not be used for POD purposes
In this
period of observation, only station AREA is present
Period 3 = between 2002.0 and 2004.0
A constant
velocity can describe the station displacement
In this
period of observation, only station AREB is present
We can
derive AREB position/velocity model from ARFB model, imposing continuity in
2002.0
ARFB model
(see after)
2000.0 ARFB
1942803.235 -5804071.591 -1796922.198 4.78 -0.75 4.40
so, when
expressed in 2004.0, we obtain
2004.0 ARFB
1942803.254 -5804071.594 -1796922.180 4.78 -0.75 4.40
the
geodetic local tie (from SIMB) is
AREB
42202S006 AREA 42202S005 -7.061 -6.369 2.771 0.002
ARFB
42202S007 AREA 42202S005 -7.107 -6.233 2.814 0.002
So we can
derive
ARFB
42202S007 AREB 42202S006 -0.046 0.136 0.043
From that,
we can derive the AREB position in 2004.0
2004.0 AREB
1942803.208 -5804071.458 -1796922.137 4.78 -0.75 4.40
Before
2004, the velocity is different (see above GPS-derived velocity), so we have
before (from 2002.0 to 2004.0):
GPS
velocity (n lat/lon/rad) is -3.61 -19.01 2.42
So, in XYZ
(ITRF2005), we obtain: -17.62 -7.26 -4.15
2004.0 AREB
1942803.208 -5804071.458 -1796922.137 -17.62 -7.26 -4.15
so we
obtain at epoch 2000.0
2000.0 AREB
1942803.278 -5804071.428 -1796922.120 -17.62 -7.26 -4.15
we can
verify using DORIS data and fixing the velocity to the GPS-derived value (from
2002.0 to 2004.0)
2000.0 AREB
1942803.3334 -5804071.4057 -1796922.1351 -17.62 -7.26 -4.15
statistics
AREB XYZ 0.0032 0.0022 0.0023 84
which is
rather close, except for the X-component
We select
to use the postion derived from ARFB + the geodetic local tie
2000.0 AREB
1942803.278 -5804071.428 -1796922.120 -17.62 -7.26 -4.15
Period 4 = after 2004.0
A constant
velocity can describe the station displacement
In this
period of observation, only station AREF is present
The
estimated GPS velocity is (lat/lon/rad) 4.85 4.30 0.89
So the
velocity in ITRF2005 (XYZ in mm) is 4.78 -0.75 4.40
By using
weekly DORIS solutions (ign07d02) and fixing the velocity to the above value
derived from GPS, we obtain :
2000.0 ARFB
1942803.2345 -5804071.5908 -1796922.1984 4.78 -0.75 4.40
statistics
ARFB XYZ 0.0030 0.0016 0.0015 77
Recommendation:
Derive AREA, AREB, ARFB positions in ITRF2000 using GPS velocity (JPL, Mike Helflin). Impose continuity in 2002.0 between AREB and ARFB, using geodetic local tie