Subject: [IGSMAIL-1900] New estimated value for GPS43 antenna phase center offset
From: Yoaz Bar-Sever
Date: Thu, 14 May 1998 16:02:45 PDT

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IGS Electronic Mail      Thu May 14 16:02:45 PDT 1998      Message Number 1900
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Author: Yoaz Bar-Sever
Subject: New estimated value for GPS43 antenna phase center offset

Dear Colleagues,

I have conducted a series of experiments designed to estimate the phase 
center offset of the transmit antenna on GPS43 (PRN13, the new Block IIR 
GPS satellite). The estimated value puts the phase center 59 cm ABOVE the 
center of mass (i.e., 59 cm along the negative spacecraft-fixed Z axis). 
This value differ significantly from the previously published values 
(see IGS Mail 1653). A standard deviation of 13 cm is associated with this 
estimate. These results are based on daily estimates of the transmit 
antenna X, Y and Z offsets, spanning 31 days in December 97 and March 98. 
The estimated X and Y offsets were statistically consistent with the 
published zero values.

The JPL IGS Analysis Center has employed  a value of -63 cm for the phase 
center offset starting with the final orbit solution of March 30. The rapid 
orbit solution has employed it since April 6. (The value of -63 cm was
based on a single day estimation, at the time.) 

The main impact of this modeling change is on the clock solution
for the satellite. Due to the high correlation between the satellite
clock and the radial phase center offset, biases in satellite clock 
estimates are to be expected between solutions using different phase
center offsets, with magnitudes similar to the difference in the offset.
Indeed, since march 30, the large bias in the clock estimates for 
GPS43 between the JPL AC solution and the solutions from other Analysis 
centers has lead to increased RMS difference between the JPL solution
and the IGS combined solution.

Sincerely,
                                         Yoaz Bar-Sever
--
 Dr. Yoaz E. Bar-Sever
 [email-masked]                  MS 238-600
 voice: (818) 354-2665 office            Jet Propulsion Laboratory
        (626) 794-9243 home              4800 Oak Grove Dr.
 FAX:   (818) 393-4965                   Pasadena, California  91109

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