Private parameters for program NSCAN
This document contains an overview of the parameter interface of the program NSCAN. The program also uses a number of public interfaces; references to these are also listed. show parameters that The remainder of the document describes the individual parameters in alphabetical order. This description centers on the Help texts, which have been designed to guide the user to the proper choice at each junction, even if his knowledge of the overall workings of the program is only superficial.
See also:
Prompt: ARC Action
Expected input: Character *24: 1 value
Checking in a WSRT tape has two phases. In the first phase, the ARC option CHECK is used to verify the general integrity of the tape. The tape is listed and all blocks are read. In the second phase labels are copied to the archive medium (with the DUMP option) and the Scissor database is updated through ARC option ARCHIVE.
Prompt: Precision for writing UVFITS output
Expected input: Integer: 1 value
Specify the precision for writing UVFITS data.
16 2 bytes integers 32 4 bytes integers -32 IEEE Floating point values (not yet supported)
Prompt: frequency channel number(s)
Expected input: Integer: 1 to 512 values
Select the frequency channels/bands to be included. NOTE that the WSRT continuum channel (i.e. the sum of all channels) always has number 0
'*' selects all channels
'<begin> TO <end>> BY <step>' selects channels <begin>, <begin>+<step>, ...
up to <end>. The 'BY <step>' part may be omitted.
BEWARE: The notation <begin>-<end>:<step> will be interpreted as an
expression and give incorrect results
Each of the selected channels will be stored in the .SCN file as a separate 'channel' (chn) under the current 'group', 'observation' and 'field' grp.obs.fld. (Remember that .SCN file 'sectors' are identified by indices grp.obs.fld.chn.seq).
Prompt: Start-offset (sec)
Expected input: Real: 1 value
Specify the time-offset from the start of an observation, at which the integration for the output scans should start. Example: an offset of n will throw away the first n (rounded up to a multiple of 10) seconds of data.
NOTE: This feature was useful in early mosaic experiments in which the slewing between fields occurred in the first integration interval(s) on the new field. It is now standard practice to slew during the final integration interval on the old source.
Prompt: MJD, leap seconds,...
Expected input: Real: 1 to 20 values
Specify the IAT-UTC values as pair(s) of numbers:
MJD at which the leap seconds occur The total number of leap seconds as from that date.
The first value is for 1 Jan 1991. Values before that are known by the program.
Prompt: integration time for total-power data
Expected input: Integer: 1 value
Specify the desired integration time for IF sets with Total Power data.
Prompt: input filename
Expected input: Character *80: 1 value
Specify the input disk-file name.
For the NSCAN LOAD-from-disk option, or for the NSCAN PFITS option, don't specify a file extension: it will be made by the program on the basis of the tape label number.
In the case of other NSCAN options, give the full file name.
Prompt: input tape labels
Expected input: Integer: 1 to 256 values
Specify the tape labels to be read.
'*' selects all labels
'<begin> TO <end>> BY <step>' selects labels <begin>, <begin>+<step>, ...
up to <end>. The 'BY <step>' part may be omitted.
BEWARE: The notation <begin>-<end>:<step> will be interpreted as an
expression and give incorrect results
Each of the selected labels will be stored in the .SCN file as a separate 'observation' (obs) in the current 'group' grp. (Remember that .SCN file 'sectors' are identified by indices grp.obs.fld.chn.seq).
Example:
If the current group nr is <g>, the selected input labels will be
stored sequentially in the .SCN file as observations <g>.0, <g>.1, <g>.2
Prompt: integration time (sec)
Expected input: Integer: 1 value
Specify the desired integration time per output scan in seconds. 120 sec is a good default; a lower value should be selected if visibilities vary rapidly as a consequence of the source distribution in the observed field, atmospheric conditions or interference.
For standard observations, the number must be a multiple of the basic integration time used for the observation (which is some multiple of 10 sec).
In WSRT mosaic observations, slewing occurs in the last 10 sec of the dwell time on each subfield. The integration time you specify must therefore at most be <dwell time> minus 10 sec. You may also use a submultiple of this value without losing data.
Example:
If the dwell time is 90 sec, there is 80 sec of valid data. HA_INT = 80,
40, 20 or 10 will use it all. However, HA_INT = 30 or 60 will result in the
loss of the last 20 sec.
The volume of your data in the .SCN depends primarily on the
integration time. For each integration interval a 'scan' is created which
consists of
<nr of polarisations> * <nr of interferometers> * 12 + 1024 bytes
Model visibilities which may be added later will occupy another
4 * <nr of interferometers> * 12 bytes . NOTE:
The WSRT runs on Universal Time; the quantum of integration time is
therefore 10 UT seconds, and a full 12-sidereal-hour observation contains
somewhat less than 12*360 of these quanta. You can mostly ignore this subtlety,
but the difference may be of practical importance in some situations.
Prompt: Old R-series data format
Expected input: Integer: 1 value
Specify the old R-series data type:
0= local
1= VAX, D_FORMAT
2= VAX, G_FORMAT
3= ALLIANT
4= CONVEX
5= IEEE
6= DEC station
7= SUN station
8= HP station
Prompt: Action
Expected input: Character *24: 1 value
Specify the action to be performed by the program NSCAN:
Operations on WSRT 'circle' observation files (on classical, DAT or Exabyte tape, magnetic or optical disk):
LOAD transfer observed visibilities into a .SCN file.
IFLOAD same, but also transfer the 'IF' data (total powers etc). The
extra data will enlarge the .SCN file by some 30%
them only if you suspect that the on-line gain calibration has
been incorrect.
LEIDEN transfer observed visibilities from standard LEIDEN file into a
.SCN file
LIST show contents of selected labels
ARC as list, but update the Scissor database if at NFRA
DUMP copy selected label(s) byte for byte into a disk file
Conversion to and listing of data in FITS format
UVFITS convert .SCN file to UVFITS tape/disk file for use in AIPS
PFITS print AIPS-like FITS info (but also other) from UVFITS file
header
Display and editing of .SCN files:
SHOW show/edit data and header information in .SCN file. (This
option is duplicated in NFLAG.)
Utilities:
QUIT leave the program NSCAN
CVX convert a .SCN file from other machine's number format
NVS convert a .SCN file to newest version. Needs only to be run if
programs report that the data has the wrong version
- calculates parallactic angle for ATNF
NOPT update contents of sector/scan headers and polarisation format
of visibility data:
- convert input data in Stokes parameter format to XX format
- calculate UT start
- calculate precession rotation angle if not filled
- recalculate MJD for observations aborted at Wbork
REGROUP create a second index for each of one or more sets of sector.
One-time fixes:
FROM_OLD convert old (R-series) uv-data file into NEWSTAR .SCN file
WERR correct one-time mosaic WSRT tape errors (1991 data only)
AERR change sign of phases
Prompt: output filename
Expected input: Character *80: 1 value
Specify the full name for the output disk file.
For the NSCAN DUMP option, don't specify a file extension: it will be made by the program on the basis of the label number.
For the other NSCAN options, specify a full file-name.
Prompt: output tape label
Expected input: Integer: 1 value
Specify the first output tape label.
* or 0 indicates the end of the tape (i.e. append the new labels at the end).
Prompt: Mosaic field sequence number(s)
Expected input: Integer: 1 to 512 values
Select the SEQUENCE numbers of the fields (= mosaic 'pointing
centres') to be selected. (see Note below).
NOTE that WSRT mosaic fields are numbered starting at 1
'*' selects all fields
'<begin> TO <end>> BY <step>' selects fields <begin>, <begin>+<step>, ...
up to <end>. The 'BY <step>' part may be omitted.
BEWARE: The notation <begin>-<end>:<step> will be interpreted as an
expression and give incorrect results
Each of the selected fields will be stored in the .SCN file as a separate 'field' (fld) under the current 'group' and 'observation' grp.obs. (Remember that .SCN file 'sectors' are identified by indices grp.obs.fld.chn.seq).
NOTE:
The numbers you specify refer to the SEQUENCE (starting with 0) in
which the mosaic fields aqppear on the tape. Normally, an observation starts
with field 0 and the sequence numbers equal the field numbers. However, if your
observation starts 'somehere in the middle', this is no longer the case and you
must be careful in selecting your fields. Example:
Your observation starts at field 19. To select fields 19 through 24,
specify POINTING_SETS= 0 TO 5.
Prompt: new index pattern (grp.obs.fld.chn.seq)
Expected input: Character *32: 1 value
Specify a new index pattern (group.observation.field.channel.sequence_number) into which to change the index pattern of the input Set of uv-data Sectors.
Each index in the pattern that contains an * is copied from the input Set. Other fields are used as is (true for the first four fields, i.e. grp.obs.fld.chn.)
Example: To change the indices of the Set
0.*.15283.* to
0.*.0 .*
give the first selection as the input Set, and the second as the pattern.
Prompt: output polarisations (ONE 'value') |
Expected input: Character *4: 1 value
Specify the polarisation(s) to be written:
I: I only
Q: Q only
U: U only
V: V only
IQ: I and Q
UV: U and V
IQUV: I, Q, U and V
X: XX only
XXY: XY only
YYX: YX only
Y: YY only
XY: XX and YY
YX: XY and YX
XYX: all four: XX,XY,YX,YY
Prompt: Which type tape
Expected input: Character *6: 1 value
Specify the type of the tape.
Currently we support two types: WSRT and LEIDEN.
Prompt: Hour-angle correction (deg)
Expected input: DoublePrecision: 1 value
Specify the angle to be added to all hour angles in the .SCN file
NOTE: This is a special feature to be used only to correct errors made in the on-line observation.
Prompt: WERR action
Expected input: Character *24: 1 value
Specify correction to be performed:
WE0: correct Hour angles for tape error in splitted mosaic tapes before
online version 62
WE1: correct all Hour angles with a constant offset
QUIT: no more
Prompt: RA of mosaic centre
Expected input: DoublePrecision: 1 value
Specify the Right Ascension of the centre of the mosaic area
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