Re: Here's what Adam said about the 20-degree earth avoidance angle:

From: Vitaliy Fadeyev (VAFadeyev@lbl.gov)
Date: Tue Jul 13 2004 - 10:30:25 PDT

  • Next message: Greg Aldering: "Re: Here's what Adam said about the 20-degree earth avoidance angle:"

    I cannot comment on the ACS orbits. With NICMOS, the story is slightly
    different, due to the multiple readouts in each exposure. The recommended
    procedure for a given exposure is to look at the rate of the sky background
    as a function of time/readout before the processing. Then if say last few
    readouts reveal a significantly higher background rate, one can remove
    them from processing, thereby effectively reducing the exposure time.

    So, in this case one has a handle to investigate and to control the
    issue of
    higher background from the data themselves. For this reason I would not
    artificially shorten the NICMOS orbits.

    vitaliy

    Saul Perlmutter wrote:

    > Here's what Adam said about the 25-degree earth avoidance angle:
    >
    > Apparently, it was the ACS and GOODS teams that started switching to
    > 25-degree avoidance (from the previous default of 20 degrees). They
    > found that there was no way they could separate out the
    > high-background part of the orbits from the dark parts of the orbits
    > (especially since orbits are sometimes stitched together to get the
    > exposure time requested), and that the hit in noise with a 20-degree
    > avoidance angle was dominating over the gain in exposure time with a
    > 25-degree avoidance angle. So Adam said that the GOODS team and
    > Adam's SN team always use the 25-degree angle now.
    > This sounds like we should switch to this too. Comments?
    >
    >
    >

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