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

From: Saul Perlmutter (saul@lbl.gov)
Date: Tue Jul 13 2004 - 11:10:02 PDT

  • Next message: Saul Perlmutter: "NICMOS use of more relaxed earth-avoidance angle."

    I asked Adam about the possibility of breaking up the orbit into enough
    separate exposures that you could isolate the bad background light
    exposures, but apparently they find that the exposures are often enough
    made from (unpredictable) parts of several different orbits that this is
    hard to do.

    I think the NICMOS idea should work, however, as Vitaliy suggests.

    Greg Aldering wrote:

    >This problem is the result of having to look over the earth to see this
    >field this time of year. Certainly we should consider restricting the
    >grism observations to > 25 degree from the earth. For z-band the damage
    >may not be bad, as we will (or could) break an orbit into several
    >exposures, and readout noise might be dominating the noise (I suppose
    >Rachel can answer this easily enough). (We could consider making the
    >exposure times unequal to better isolate the bright parts.) As for NICMOS,
    >I don't really know whether the problem of the earth's limb is all that
    >bad as I expect less scattering at red wavelengths, and if we are
    >processing the up-to-ramp data we could just deweight the bright times
    >(Vitaliy, is that possible?).
    >
    >- Greg
    >
    >
    >On Tue, 13 Jul 2004, 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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