Tecniche terrestri di rilievo applicate alle antenne VLBI per lo studio delle deformazioni gravitazionali P. Sarti, C. Abbondanza, S. Montaguti, M. Negusini, L. Vittuari
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