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#1
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[fitsbits] Format for multi-readout, multi-amplifier data
Dear FITSbits-readers,
What would be reasonably standard formats for multi-readout, multi-amplifier data? In this case a 4-amplifier near-IR array in non-destructive read-out mode, used both for imaging and spectroscopy? The observers are unlikely to appreciate N_amp * N_readout extensions, although this is the preferred format I guess from the FITS point of view. Are there other formats in use, which allow for different amplifier characteristics and are observer-friendly at the same time? Best regards, Saskia Prins - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - Saskia Prins Nordic Optical Telescope Apartado de Correos 474 Tel: +34-922-425448 38700 Santa Cruz de La Palma Fax: +34-922-425475 Canarias, Spain - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - |
#2
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Saskia Prins,
Are there other formats in use, which allow for different amplifier characteristics and are observer-friendly at the same time? I think the most observer-friendly format would be a data cube in the primary header/data unit, with N_readout elements in the third dimension. You could have a separate file for data from each of the four amplifiers, or you could use four IMAGE extensions. Phil |
#3
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In article rao.edu,
Saskia Prins writes: What would be reasonably standard formats for multi-readout, multi-amplifier data? In this case a 4-amplifier near-IR array in non-destructive read-out mode, used both for imaging and spectroscopy? Such arrays (and ones with even more readouts) are widely used in astronomy. At the stage where you have reduced the data to a single brightness number for each pixel, most astronomers will appreciate a single primary image with x,y corresponding to pixel position on the array. Then it's easy to apply calibrations and add a WCS in either spectral or positional coordinates. At stages of the reduction prior to the above -- for example if you are using "sampling up the ramp" in post-processing -- do whatever is most convenient for the data collection and reduction software. Few if any humans are going to look at the data at that stage. I can imagine using tables or a 3d image with the third axis being sample number. For example, with IRAC on Spitzer, when we do pedestal- signal sampling, the pedestal and signal frames are in separate files. The point is not that this is a good idea or recommended practice; it's that anything will work OK for the early stages. It's only the later stages that matter to most users. -- Steve Willner Phone 617-495-7123 Cambridge, MA 02138 USA (Please email your reply if you want to be sure I see it; include a valid Reply-To address to receive an acknowledgement. Commercial email may be sent to your ISP.) |
#4
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I assume the 4 amplifiers are reading quadrants of one physical
detector? If so, this is the same as the NICMOS and WFC3 IR cameras on HST (well, *will be* in the case of WFC3). Since the data from the 4 amps produces what amounts to one contiguous image of the sky, that's the way we've always packaged them in FITS files. You stitch the data from the 4 amps for a given readout together into one image, stored in one image extension. So then you have N_readout extensions, not N_amp*N_readout. The same is done for our CCD instruments that use 2 amps to read one physical chip: the data from the 2 amps is stiched together into a single image, which is in turn stored in one image extension. Only when there's a physical discontinuity, such as multiple chips butted together into one focal plane, do we split the data into separate FITS extensions. -Howard Bushouse WFC3 and ex-NICMOS calibration programmer Saskia Prins wrote: Dear FITSbits-readers, What would be reasonably standard formats for multi-readout, multi-amplifier data? In this case a 4-amplifier near-IR array in non-destructive read-out mode, used both for imaging and spectroscopy? The observers are unlikely to appreciate N_amp * N_readout extensions, although this is the preferred format I guess from the FITS point of view. Are there other formats in use, which allow for different amplifier characteristics and are observer-friendly at the same time? Best regards, Saskia Prins - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - Saskia Prins Nordic Optical Telescope Apartado de Correos 474 Tel: +34-922-425448 38700 Santa Cruz de La Palma Fax: +34-922-425475 Canarias, Spain - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - |
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