SMART Error and BMASK Planes

SMART Error and BMASK Plane Processing

IRS Basic Calibrated Data (BCD) is usually supplied in the form of three corresponding files. All three are 128 X 128 FITS image files :

  1. A data file, name ending "_bcd.fits". This contains an array image from the relevant IRS module. (One of SH, SL, LH or LL).
  2. An error plane file, name ending "_func.fits". This contains best estimate values for errors (noise) in the corresponding "bcd.fits" data file pixels.
    It is supplied by the SSC with the IRS data and referred to as the "SSC Error Plane".
  3. A bitmask file, called "BMASK", name ending "_bmask.fits". This contains a 16 bit binary number indicating possible error conditions for each corresponding "bcd.fits" data file pixel.

The meanings of BMASK bit values are :

Decimal Power Hex Value Description
2 2^1 hex 2 Latent-image flag
4 2^2 hex 4 Digital saturation detected in sample(s) along ramp
8 2^3 hex 8 Radhit detection along ramp in sample(s) along ramp
16 2^4 hex 10 Non-linearity correction could not be computed in sample(s) along ramp
32 2^5 hex 20 Data bad (initial dmask; radhit checks this bit) in sample(s) along ramp
64 2^6 hex 40 Droop or rowdroop removed using questionable value in sample(s) along ramp
128 2^7 hex 80 Flat field applied using questionable value (flatap)
256 2^8 hex 100 Flat field could not be applied (flatap)
512 2^9 hex 200 Stray-light removal or crosstalk correction not applied
1024 2^10 hex 400 Saturated - beyond correctable non-linearity in sample(s) along ramp
2048 2^11 hex 800 Data missing in downlink in sample(s) along ramp
4096 2^12 hex 1000 Only one usable plane
8192 2^13 hex 2000 No usable planes
16384 2^14 hex 4000 Pixel masked in pmask

SMART will accept and process input IRS data in either 1-plane or 3-plane form :

  1. 1-plane data.
    Only the "bcd.fits" data file is loaded into SMART. (See Dataset Manager for a description of how to load data into SMART. In this case SMART will internally generate both an error plane and a BMASK plane and use these for extraction processing. SMART generated error plane values are all initially set to zero. SMART generated BMASK plane values are all initially set to zero.
  2. 3-plane data. For all three planes of a single observation to be loaded into SMART they must first be combined into a single "3-plane" type FITS file, usually designated "bcd3p.fits". SMART provides scripts for making 3-plane data, see Provided Scripts? and Procedure Headers?. The resulting 3-plane files can then be loaded into SMART. (See Dataset Manager for a description of how to load data into SMART.)

SMART Error and BMASK Plane - (SMART Parameters Advanced window)

How the error and BMASK planes are used during SMART processing can be controlled by changing certain SMART SMART Parameters (advanced).

The relevant parameters are :

  1. sm_eplane Values :
    1. "SMART Constructed Error Plane"
    2. "SSC Error Plane"

    System Default : "SSC Error Plane"

    If 1-plane data is being used then the setting of this parameters is irrelevant. A SMART internally generated error plane will always be used because there is nothing else available. If 3-plane data file is being used the results are dependent on the "sm_eplane" parameter setting :

    1. SMART Constructed Error Plane - an initial error plane with all error values equal to zero is used. When using SMART Image Operations SMART generated error plane values are the statistical variance of the corresponding flux values. For more information see : Errors and BMAKS during Image Operations.
    2. SSC Error Plane - the SSC supplied error (noise) plane is used.
      For more information see : Errors and BMAKS during Image Operations.

  2. BMASK Value Selection Display

    Values : ON or OFF for each of 14 radio buttons

    System Default : OFF for each

    This is used during extraction. Each indivdual pixel can be included or ommited from extraction depending on its corresponding BMASK value.

SMART Error and BMASK during Image Operations

For more information see : Errors and BMASK during Image Operations.

 
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