[daip] SDA in VLA datasets

[Bryan Butler]

hi douglas,

eric forwarded your question on to me regarding looking
at information in the SDA ("Subarray Data Area") within
uv datasets.

most of this information is thrown out when the data is
read in to AIPS (well, it is often used to make decisions
on what to do with data, e.g., flagging or not, but then
not recorded anywhere within the AIPS uv dataset).

however, it is retained in the archive data file, and i
can get that information for you if you wish.  is this
the same vela dataset you had me looking at Tsys for?

i gather you want the information in section D.9 of memo
186 ("Array Control Bits")?  you should know that the
bit that indicates correlator gating is a bit suspect
(pardon the pun).  i asked ken sowinski about it a few months
ago (i was doing some debugging of a program to parse those
bits), and he indicated that it doesn't always map one-to-one
with what's actually going on in the correlator.  i've
cc:'ed him onto this email in case he wants to chime in
here (if i've misinterpreted what he told me then).  here
is a bit of an email exchange between he and i on this
topic:

bryan wrote:
>>  - in the "Array Control Bits" words in the archive, is bit 4
>>    ever actually turned on?  this is the bit that is supposed
>>    to be "correlator is gated for pulsar observations".  walter
>>    tells me that there is no information in the archive that
>>    indicates pulsars are being observed.  it might just be that
>>    FILLM knows nothing about this bit (or doesn't use it anyway).

to which ken replied:
>What is really means is that "this is an observation which gates
>the correlator".  I suppose that includes some pulsar observations
>but not necessarily all.  It is needed to force AP software to 
>really use the V_s the correlator reports even though it is not
>the theoretical V_s expected based on the integration time.  The
>default is to use the theoretical in case of a difference.

if you let me know the date + timerange that you want this 
information, i can extract it from the raw data archive
files and send it on to you.


	-bryan

p.s. vla computer memo 186 is superseded by vla computer memo 188...
most of the information is the same, but some is different.