Tecniche terrestri di rilievo applicate alle antenne VLBI per lo studio delle deformazioni...

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