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A problem with the DFE (Dark Frame Error) correction (updated Mar 5, 1995)

The problem described below applies to FTOOLS version 3.2 and earlier. If your software is version 3.3 or later, and your data have been processed with version 3.3 or later, then you can safely ignore this bulletin.

Recently, it was discovered that the FAINT FTOOL occasionally fails to carry out the DFE (Dark Frame Error) correction. The origin of the problem was located in the part of the source code which reads the DFE filename.

This problem may impact data analysis for FAINT -> BRIGHT2 converted data, i.e., those data for which both the Echo and DFE corrections are carried out. It does not affect the analysis of BRIGHT mode data. Please refer to Otani et al. 1994 in ASCA Newsletter vol.2 for details of Echo and DFE corrections. For convenience, if you click here, you can find a short description of the three SIS imaging modes (FAINT, BRIGHT and BRIGHT2) as well as DFE. You can skip over it if you're already familiar with the material. A description of the problem - with solutions - is next.

The Problem:

In the FAINT FTOOL, the parameter "dfefile" is used either for constant DFE values or for the name of a dfefile. The program was supposed to recognize the DFE values as being REAL variables and dfefile name as a CHARACTER string, but it turned out that in some cases the dfefile name is read, unexpectedly, as a REAL value (0.0 or -1.0, as far as we are aware). Consequently, in some cases, constant DFE values (0.0 or -1.0) are incorrectly used instead of reading in the dfefile. This behaviour has been found to depend on the system architecture (i.e., the compiler).

In fact, it appears that the only cases for which the dfefile name is always correctly recognized by the FAINT FTOOL are:

  • SunOS is used and the first character of the dfefile name is not a "/" (unfortunately not the case when FAINT is invoked from XSELECT)
  • VMS is used and FAINT is invoked from XSELECT.
The DFE file name is NOT recognized and the DFE correction fails , for Unix (SunOS, Ultrix, Alpha/OSF) when the first character is "/". Unfortunately, the XSELECT "faint" command specifies the dfefile name with the absolute path ("/" in the beginning). So DFE correction carried out using the XSELECT "faint" command is incorrect.

The DFE file name may or may not be recognized for VMS, Ultrix and Alpha/OSF. This is not simply predictable. For example, "a.dfe" is recognized, but "ft930912_1638_1810S003701H.dfe" is not recognized.

Versions of FAINT up to 3.3b have this problem (the latest public version is 2.8a, corresponding to the FTOOLS version 3.2). The problem is fixed in the next version of FAINT (version 3.3e; FTOOLS version 3.3).

Impact of This Problem:

The impact of this problem is as follows.

  1. PV / Archival data

    The PV/archival data are all processed under SunOS and the dfefile is specified without a "/". Consequently, the DFE correction in the PV/archival data is correct.

  2. GO data processed at GSFC

    In the middle of AO2, DFE correction was applied to GO data processed at GSFC. If you have *12[HM].fits files in your package, these are FAINT --> BRIGHT2 converted data which were supposed to be DFE and echo corrected. To determine whether you have incorrect BRIGHT2 data:

    Please find the ad********.joblog file, located in the 'product' directory (******** is the sequence number).

    In the beginning of the log, you will see,

    AO:A4.8.1:LO:Start at Thu Nov 3 11:05:04 EST 1994
    AO:A4.8.1:LO:Hostname addev
    AO:A4.8.1:LO:Processing directory /data16/ao/seq_proc/42010000.001
    AO:A4.8.1:LO:Process num = 6126
    AO:A4.8.1:LO:Process script = ao4.8.3.ksh

    Please check the process script name ("ao4.8.3.ksh" above), and it will tell you the script version (4.8.3 in this case). The FAINT --> BRIGHT2 conversion is made in the script version 4.6 and later. If your script version is earlier, you will not have the BRIGHT2 data.

    The date of the processing is on the first line. The data processed in 1994 are all done under ultrix, so the DFE correction will be incorrect.

    If your data were processed in 1995, please check the Hostname. "addev" and "astrod" are both Ultrix machines. If your data is processed on either of the Ultrix machines, then the DFE correction will be incorrect.

  3. GO data analysis

    If you have used the 'faint' command in XSELECT, then your DFE correction will probably be incorrect. If you ran the FAINT FTOOL by itself under SunOS, then the DFE correction will be correct unless you specified the absolute path of the dfefile. If you ran FAINT under VMS, Ultrix or Alpha/OSF, then the DFE correction may or may not be correct. However, please note that if the dfefile name started with "ft*" then the DFE correction will certainly be wrong.


In order to re-do the DFE correction, please install FTOOLS version 3.3 which was released on Feb 27, 1995. The easiest way is to apply the DFE correction is to run "ascascreen", choosing to analyse the FAINT data. Ascascreen is a Perl script which is included in the FTOOLS package, and automatically creates a command macro to run XSELECT.

If you prefer to work by hand from within Xselect itself, do:

xsel:ASCA > set datadir whatever
xsel:ASCA > set inst sis0
xsel:ASCA-SIS0 > set datamode faint
xsel:ASCA-SIS0-FAINT > make obscat
xsel:ASCA-SIS0-FAINT > choose 1-**
xsel:ASCA-SIS0-FAINT > faint bright=b2 dfefile=MAKE echo=-99 maxgrade=4 split=40

Then :

xsel:ASCA-SIS0-FAINT > save faint

to save all the files.

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This file was last modified on Monday, 13-Sep-1999 15:37:01 EDT

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