[IGSMAIL-1535] ALGO Antenna change 15-16 January

[Robert]

******************************************************************************
IGS Electronic Mail      Tue Feb  4  5:37:01 PST 1997      Message Number 1535
******************************************************************************

Author: Robert Duval / NRCan
Subject: ALGO Antenna change 15-16 January

 
ADVISORY
========

Site name          : ALGONQUIN       
4 char ID          : ALGO    
Monu inscription   : 883160            
Domes number       : 40104M002  


The reported antenna swap at ALGO was done on Jan 15/97 at about
midnight
UT (IGSMAIL# 1522). No significant phase centre changes were expected as
the new (S/N #386) and the original (S/N #173) antennas are of the same
type (DORNE MARGOLIN T), the only difference is that the new one has a
new
RF (low noise) filter. In order to verify that no significant antenna
phase
centre changes indeed occurred a nearby station (about 86m from ALGO)
was
occupied with Turbo Rogue & Dorne Margolin T antenna for two days, one
day
before (Jan 15) and one day after the change (Jan 16). Since the nearby
station did not move (a force centred concrete pillar) and no
significant
changes occurred in the surrounding (the reflective/multipath)
environment
during the two days, it is expected that this station could verify (or
detect) any phase centre (pc) changes at ALGO caused by the above
antenna
change. In the table below the change at ALGO (Jan 16-Jan15, or
#386-#173)
are listed for L3, L1 & L2 solutions. For this a regular IGS processing
(i.e. stochastic tropo modeling & solutions) were used, though changes
of
up 3 mm (in the height only) were observed when tropo scaling was not
solved or solved as a single parameter only.


Difference at ALGO phase centre (Jan 16(S/N#386)-Jan 15(S/N#173) in mm

         	L3                  L1                  L2
 North        -2.5 +-.5mm      -.4  +- .2mm       .9  +- .3
 East         -1.9   .5        -.3     .2         .9     .3
 Up           -2.1  2.8       -2.8    1.1       -3.2    1.5
 Length       -1.0   .5        -.2     .2         .3     .3

AS can be seen above the antenna pc changes could be considered
insignificant at a mm level, in particular for the height, when taking
into
account the formal sigmas, and the fact that the same order of magnitude
(height) variation was observed by changing the tropo scale (solution)
modeling.

-- 
Robert Duval

Geodetic Survey Division, 
Natural Resources Canada (NRCan)              
615 Booth Street                       
Ottawa, Ontario, K1A 0E9
Tel:    (613) 947-2786    Fax:    (613) 995-3215
E-mail: duval at geod.nrcan.gc.ca
*****************************************************************************


[Mailed From: Robert Duval <duval at geod.emr.ca>]