Tab1 4 Co
e
mpanson 0 f recen t SLR 1 t'
so u IOns or zona 1 h
t
armomc ra es
I Investigation
I
.
I
.
I
.
I
.
I
.
I
J~
J~I
J~
J~
J~
Yoder et al. (1983):
-3.0
L-1
±0.3
Rubincam (1984)
-2.6
L-1
+0.6
Cheng et al.(1989)
-2.5
1.2tt
-0.1
0.3
1.5
Str
+0.3
±0.3
+0.6
+1.5
Nerem & Klosko (1995)
-2.1
2.3 t
-0.05
L-1, Ai, Str: 1986-92
+0.3
+0.4
+1.6
Cheng et aJ. (this issue)
-2.7
l.4tt
-0.4
-1.3
2.1
L-1,L-2, StJ, Str, Ai, BEC
+0.5
+0.7
+1.0
+0.7
Cazenave et al. (this
-3.00
-1.78
-0.8
issue) L-1, L-2
+0.3
±0.1
±1.5
This Study: L-l, L-2, Aj,
-2.77
1.57
0.20
Str: 1986-94
,::.
+0.25
+0.35
+1.46
n'
.
mferred from (eq. 3) usmg 1) and J s ,
t without Lageos-2 as used. in this. study, th.e lumped coefficient has a different
sensitivity to J s as follows: J)L = J) + 1.17 J s
Key: L1 Lageos-l, L2 Lageos-2, Str Starlette, Aj Ajisai, Stl Stella
determined uniquely from the gravitational potential it generates. Obviously, this decoupling
is made more complicated when many of the geophysical processes share dominant signals
of similar character. Nevertheless, the optimum combination of satellite-derived global
information with related geophysical models can provide important modeling improvements
and insights through their complementary boundary conditions. With three well determined
zonal harmonic rates (Jz, J 4 and lumped J 3 -J S ) and the obselVed secular variation in the
orientation of the Earth's spin axis (X and Y), the strength of this inverse method can at
least be demonstrated. The results herein will clearly improve as temporal gravity changes
are better spatially and temporally resolved, and through supporting geodetic studies of
crustal displacements themselves [cf., James and Ivins, 1994].
T bl 5 Ob
d
a e .
selVe secu ar po ar motIOn rates
I
I
I
X
I
. I
AUTHOR
DESCRIPTION
Y
(mas/y)
(mas/y)
Gross ~1994~: Space'93
• SLR, VLBI, GPS, LLR
0.78
3.98
Gross 1982: Thesis
• ILS data
1.34
3.67
Wilson & Vicente ~1980)
• ILS data
1.39
3.09
Trupin et al., (1993
• 1965 to 1984
0.78
2.26
Least sq fit (Fig 1a-1d)
• IERS (1986 to 1994)
-0.45
5.61
158
e
mpanson 0 f recen t SLR 1 t'
so u IOns or zona 1 h
t
armomc ra es
I Investigation
I
.
I
.
I
.
I
.
I
.
I
J~
J~I
J~
J~
J~
Yoder et al. (1983):
-3.0
L-1
±0.3
Rubincam (1984)
-2.6
L-1
+0.6
Cheng et al.(1989)
-2.5
1.2tt
-0.1
0.3
1.5
Str
+0.3
±0.3
+0.6
+1.5
Nerem & Klosko (1995)
-2.1
2.3 t
-0.05
L-1, Ai, Str: 1986-92
+0.3
+0.4
+1.6
Cheng et aJ. (this issue)
-2.7
l.4tt
-0.4
-1.3
2.1
L-1,L-2, StJ, Str, Ai, BEC
+0.5
+0.7
+1.0
+0.7
Cazenave et al. (this
-3.00
-1.78
-0.8
issue) L-1, L-2
+0.3
±0.1
±1.5
This Study: L-l, L-2, Aj,
-2.77
1.57
0.20
Str: 1986-94
,::.
+0.25
+0.35
+1.46
n'
.
mferred from (eq. 3) usmg 1) and J s ,
t without Lageos-2 as used. in this. study, th.e lumped coefficient has a different
sensitivity to J s as follows: J)L = J) + 1.17 J s
Key: L1 Lageos-l, L2 Lageos-2, Str Starlette, Aj Ajisai, Stl Stella
determined uniquely from the gravitational potential it generates. Obviously, this decoupling
is made more complicated when many of the geophysical processes share dominant signals
of similar character. Nevertheless, the optimum combination of satellite-derived global
information with related geophysical models can provide important modeling improvements
and insights through their complementary boundary conditions. With three well determined
zonal harmonic rates (Jz, J 4 and lumped J 3 -J S ) and the obselVed secular variation in the
orientation of the Earth's spin axis (X and Y), the strength of this inverse method can at
least be demonstrated. The results herein will clearly improve as temporal gravity changes
are better spatially and temporally resolved, and through supporting geodetic studies of
crustal displacements themselves [cf., James and Ivins, 1994].
T bl 5 Ob
d
a e .
selVe secu ar po ar motIOn rates
I
I
I
X
I
. I
AUTHOR
DESCRIPTION
Y
(mas/y)
(mas/y)
Gross ~1994~: Space'93
• SLR, VLBI, GPS, LLR
0.78
3.98
Gross 1982: Thesis
• ILS data
1.34
3.67
Wilson & Vicente ~1980)
• ILS data
1.39
3.09
Trupin et al., (1993
• 1965 to 1984
0.78
2.26
Least sq fit (Fig 1a-1d)
• IERS (1986 to 1994)
-0.45
5.61
158