July 26, 2006
ALMA Pointing
12
Basic Pointing Model
Az axis offset/misalignment east-west (west = positive)
DA = -AW tan(E) cos(A)
DE = +AW sin(A)
AW
Az axis offset/misalignment north-south (north = positive)
DA = -AN tan(E) sin(A)
DE = -AN cos(A)
AN
Nominal Cause
Correction Formulae
Non-perpendicularity between the Az and El axes
DA = -NPAE tan(E)
NPAE
Non-perpendicularity between the boresight and El axis
DA = -CA sec(E)
CA
HookeÕs Law vertical flexure
DE = +HECE cos(E)
HECE
El encoder zero-point offset
DE = +IE
IE
Az encoder zero-point offset
DA = -IA
IA
Term
Acom = Ademand+DA
Ecom = Edemand+DE
DA = Œaif(A,E)
DE = Œbig(A,E)
Small coefficient / non-zenith tracking assumed.