Polarimetry Support

[Chris Phillips]

Support for parallactic and feed angles should be added into ASAP v2

Changes needed are:

File format

Parangle is currently in main table, Denoted Pa below

Feed rotation is either the "angle" or "rotation" column in Focus subtable (need to check). Denoted Fr below.

The focus table should have the following columns added

Hand (either +1 or -1 depending if A=X B=Y or X=Y, B=X. default 1)

Mount (angle how the feed has been bolted into receiver package. Default 0. Pm below)

User (User definable correction. Default 0. Pu below)

The current polarisation type probably needs to be generalised a little to support single XX, YY, RR or YY

Two further possible entries (has to be zero currently) for the FOCUS subtable is xyphase (measurement of the xy phase offset) and xyphase offset (position of Cal, default 0)

Stokes Derivation

The existing Stokes derivations should be changed as follows to take into account paralactic and feed rotation

Linear -> Circular No changed needed

Linear -> Stokes

Refer to Equation 10 & 11 in Simon Jonstones discussion note.

For ASAP Equation 10 should be rewritten as:

I = C1 + C2

Q = C1 - C2

U = C3

V = C4

Then Eqn 11 can be used where FD_HAND is "hand" in the focus table, the angles used are the sum (Pa+Fr+Pm+Pu) as defind above. If Theta=Pa+Fr+Pm+Pu

It = I

Qt = Qcos(theta) - Usin(theta)

Ut = Qsin(theta) + Ucos(theta)

Vt = hand*V

Also for conversions from Stokes use

RR = (I+V)/2

LL = (U-V)/2

XX = (I+Q)/2

YY = (I-Q)/2

[Malte Marquarding]

Done. Needs to be seen that the algorithm is correct.