1. VLBI2010 Reference antenna for antenna deformations and site ties East Coast Geodetic VLBI Meeting 23-24 Feb, 2011, Haystack Observatory Bill Petrachenko

2. Using a small reference antenna for antenna deformations and site ties Small reference antenna Use connected element interferometry to a small nearby antenna to measure the “effective” reference point of the VLBI2010 antenna - and to measure the effect of VLBI2010 antenna deformations Observe GNSS satellites with the same small antenna and measure the “effective” reference point of the GNSS antenna The intersection of axes of the small antenna becomes the reference point for both VLBI & GPS and ties the techniques VLBI2010 antenna GPS antenna

3. 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; T sys = 80-K Centre freq = 8.5-GHz BW = 1-GHz T INT = 60-s Single-polarization SNR min = 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 (S T ) Median correlated flux (S m ) over UV-plane Delay error, median for UV-plane I used median values for ensemble of sessions observed

4. 3-m 2.5-m 2-m Number of sources available for a 2-, 2.5-, or 3-m reference antenna correlated with a 12-m VLBI2010 antenna

5. 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: G i = 32-25*log 10 (θ) The multipath signal phase is offset by 90 deg from the direct signal.