Tecniche terrestri di rilievo applicate alle antenne VLBI per lo studio delle
deformazioni gravitazionali
P. Sarti, C. Abbondanza,
S. Montaguti, M. Negusini, L. Vittuari
Summary
• Space geodetic instrument reference point:– Definition (conventional, stochastic, electronic)– Stability
• Local ties and eccentricity vectors• Investigation on gravitational deformations affecting
Medicina’s VLBI telescope:– Terrestrial measurements:
• Topography• Laser scanning
– Finite Element Model• An elevation-dependent signal path correction model:
– Combination of deformations– Signal path variation
Reference point: conventional definition
Fixed axis
Moving axis
Antenna Reference Point (ARP)
OTelescope Invariant Point
Reference point: electronic definition
i. frequency dependentii. elevation dependent
Reference point: stochastic definition
a. RP is realized using observations performed by space techniques
b. RP is realized with terrestrial surveying− Direct method− Indirect method− Hybrid method
GPS survey approach
j-th horizontal circlej-th horizontal plane
j-th “horizontal” sphere
i-th vertical circlei-th vertical plane
i-th “vertical” sphere
Medicina: visione globaledella rete locale
20m
N
Medicina:posizione degli
strumenti geodetici spaziali
GPS
VLBI
Medicina:dettaglio deisegnalirilevatisul radiotelescopio
P1
(mm)P3
(mm)G7
(mm)
GPS ARP(mm)
VLBI IP
(mm)
2002-2001
X -1.87 -1.87 3.17 -1.51 2.08
Y 1.57 -2.85 0.01 -0.81 2.09
Z 0.57 -2.38 -0.53 2.48 -0.13
mod 2.51 4.16 3.22 3.01 2.95
2003-2001
X -6.32 -6.32 6.45 -3.51 9.69
Y 4.73 -0.32 0.68 -4.32 -0.77
Z 0.89 -3.14 0.84 1.83 -0.42
mod 7.94 7.06 6.54 5.86 9.73
U IPF=17.6933±0.0007 (m)
U IP0=17.7003±0.0008 (m)
U IPE=17.7030±0.0003 (m)
(U IPE -U IPF) 1 cm
O
eOD f cose
Df
Receiver
Focal length
Vertex
Clark and Thomsen 1988
VRFL VRF
F
Elevation 90 deg
Elevation 75 deg
Elevation 60 deg
Elevation 45 deg
Elevation 30 deg
Elevation 15 deg
g
g
g
0 10 20 30 40 50 60 70 80 90
-10
0
10
20
30
40
Focal length variation (Laser)
(m
m)
Elevation (deg)
VRFL VRF
R
Displacement of the receiver
g
Displacement of the receiver
g
Displacement of the receiver
g
Displacement of the receiver
g
0 20 40 60 80 100-3
0
3
6
9
12
15
18
Dis
pla
cem
en
t (m
m)
Elevation (deg)
Topography FEM
R2
0 20 40 60 80 100-3
0
3
6
9
12
15
18
Dis
pla
cem
en
t (m
m)
Elevation (deg)
Topography FEM
R1
0 20 40 60 80 100-3
0
3
6
9
12
15
18
Dis
pla
cem
en
t (m
m)
Elevation (deg)
Topography FEM
R3
0 10 20 30 40 50 60 70 80 90
-10
0
10
20
30
40
Focal length variation (Laser)
Receiver displacement (Topography)
(m
m)
Elevation (deg)
FVRL FVR
V
g
Displacement of the vertex
g
0 10 20 30 40 50 60 70 80 90
-10
0
10
20
30
40
Focal length variation (Laser)
Receiver displacement (Topography)
Vertex displacement (FEM)
(m
m)
Elevation (deg)
0 10 20 30 40 50 60 70 80 90
-10
0
10
20
30
40
Focal length variation (Laser)
Receiver displacement (Topography)
Vertex displacement (FEM)
(m
m)
Elevation (deg)
FVRL FVR
56.11
44.01
56.014
1ln8
2
20
20
2
RV
RF
R f
r
r
f
0 10 20 30 40 50 60 70 80 90
-10
0
10
20
30
40
Receiver displacement (Topography)
Vertex displacement (FEM)
Focal length variation (Laser)
Path length variation
(m
m)
Elevation (deg)
0 10 20 30 40 50 60 70 80 900
5
10
15
20
25
R
ece
ive
r d
isp
lace
me
nt (
mm
)
Elevation (deg)
Astronomical measurements
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