[daip] [!6280]: AIPS - Dispersive delay fitting in AIPS

[Adam Deller]

Adam Deller updated #6280
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Dispersive delay fitting in AIPS
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           Ticket ID: 6280
                 URL: https://help.nrao.edu/staff/index.php?/Tickets/Ticket/View/6280



Hi Eric,

Perhaps the phases are set to the result of single-band delay * freq, but in practice my experience is that they are far more precise than the single-band delays, which I guess must mean that the single-band delay is being tweaked to get the right band-edge phase.   Say the correct delay and phase is 0, and you are observing with a 16 MHz band at 8 GHz.  FRING could very easily give you a delay of 0.0625 ns, which would give you the same band-edge phase and a slope of about a third of a degree across the 16 MHz.  Hence, unless your S/N is extreme, you probably won't get exactly the right delay, but you *will* get approximately the right phase.  You have a factor of 1 over the fractional bandwidth more leverage on the phase than the on the delay, in other words.  So I don't think fitting to the single-band delays alone is a good idea.

My expectation is that using the single-band delays to set an initial value (for delay and dispersive delay) and then optimising to fit the phases is the way to go.

Cheers,
Adam



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