VLBI2010 Reference antenna for antenna deformations and site ties

East Coast Geodetic VLBI Meeting

23-24 Feb, 2011, Haystack Observatory

Bill Petrachenko

Using a small reference antenna for antenna deformations and site ties

Small reference antenna

Use connected element interferometryto a small nearby antenna to measurethe “effective” reference point of the

VLBI2010 antenna- and to measure the effect of

VLBI2010 antenna deformations

Observe GNSS satellites with the samesmall antenna and measure

the “effective” reference point of the GNSS antenna

The intersection of axes of the smallantenna becomes the reference point forboth VLBI & GPS and ties the techniques

VLBI2010 antenna

GPS antenna

Question 1: Are there enough strong sources to correlated with a small reference antenna?

System parameters Ref. antenna: D = 2-, 2.5, or 3-m; eff = 0.5; Tsys = 80-K Centre freq = 8.5-GHz BW = 1-GHz TINT = 60-s Single-polarization SNRmin = 10

Sources selected from the Bordeaux Image Gallery 834 candidate VLBI sources Each oberved 1 to ~40 times in S-, X-, K-, and/or Q-band Parameters in the data base

Total flux (ST) Median correlated flux (Sm) over UV-plane Delay error, median for UV-plane

I used median values for ensemble of sessions observed

3-m 2.5-m 2-m

Number of sources available for a2-, 2.5-, or 3-m reference antenna

correlated with a 12-m VLBI2010 antenna

Question 2: Is GPS multipath small enough using a small parabolic reference antenna?

Worst case assumptions Multipath reflector is horizontal with 100% reflection

coefficient Sidelobe gain for the ref. antenna is according to the

ITU equation: Gi = 32-25*log10(θ) The multipath signal phase is offset by 90 deg from the

direct signal.

Worst Case GPS Multipath

0

1

2

3

4

5

6

0 5 10 15 20

Elevation angle (deg)

Ran

ge

erro

r (m

m)

f=1.2 GHz,D=2.0

f=1.2 GHz,D=2.5

f=1.2 GHz,D=3.0

f=1.6 GHz,D=2.0

f=1.6 GHz,D=2.5

f=1.6 GHz,D=3.0