From John Carpenter
Hi Gene and Roc,
As a starting point for a discussion, Mike asked me to make a recommendation
on which keywords should be retained in the image headers if we are
to apply a filter to remove certain parameters. At the url
http://www.astro.caltech.edu/~jmc/2mass/v3/images/hdr.html
I list an example FITS header and color-code in blue the keywords that in
my opinion should be *kept*. I thought it would be best to iterate on this
before Tuesdays telecon. Note that the current values of the "filter"
keywords are j/h/k. The bands should be capitalized, and "k" should be "Ks".
A few additional, but non-essential, comments:
(1) It would be convenient to convert UT_DATE/UT to an EPOCH keyword that
can be read in as a floating point number. This would mainly be use useful
for proper motion studies.
(2) The 2MASS visualizer allows you to specify a date/scan-number/image.
The data/scan-number are available in the header, but the image number
doesn't appear to be. Is that correct? Would it be easy to add that
information to the image header (not the images on tape, but as part
of the filtering process)? This is not essential, but it would allow
someone to unambiguously re-specify an image for the survey visualizer.
(This would be more useful if in the longer term we release all images.)
(3) We discussed this quite a while ago, but it would also be useful to add
the RA/DEC of the glints/persistence to the image header.
John
From: Mike Skrutskie
Great. As I mentioned in the telecon, I'm worried about
SKYSIG in the compressed images. SKYSIG refers to the
uncompressed value. Presumably this is corrupted in compression?
From: Gene Kopan
John,
I think the "CALID" is probably a better tracer that the last 4
lines. Also the DYFS tells the scan direction, which could be useful. I
think it is better to leave the glints/persistence in a separate file, as
the number is quite variable, and the definition can be fuzzy.
gene
From: Gene Kopan
John,
No, the saturation limit is not in the image fits header. It is on
the order of 8000 dn, roughly 1/4 of the saturation level in the flattened
frames. It is not a hard limit, but curves over as the average of the
flattened frames which soft saturate, and is also affected by various
background adjustments in the pipeline.
gene
Additional comments from John Carpenter
The following header variables are not essential and still could eliminated:
ORDATE/SCANNO - ordate/scanno/image could be useful as a group, but since
"image" is not in the header, ordate/scanno could be eliminated.
SEESH - could be misinterpreted as true seeing value
BITPIX = 16
NAXIS = 2 / # of Axes
NAXIS1 = 512
NAXIS2 = 1024
BLOCKED = T / TAPE MAY BE BLOCKED IN MULTIPLES OF 2880
EXTEND = T / TAPE MAY HAVE STANDARD FITS EXTENSIONS
ORDATE = '990813 ' / Observation Ref Date (yymmdd)
DAYNUM = '0896 ' / Observation Day Num
FN_PRFX = 'k0896018' / .rdo and .par filename prefix
TYPE = 'sci ' / Scan type: dar flt sci cal tst
SCANNO = 18 / Scan Number
SCANDIR = 's ' / Scan Direction: n, s, -
COMMENT (OV)
STRIP_ID= 320918 / Strip ID (OV)
POSITNID= 's421701 ' / Position ID (OV)
ORIGIN = '2MASS ' / 2MASS Survey Camera
CTYPE1 = 'RA---SIN' / Orthographic Projection
CTYPE2 = 'DEC--SIN' / Orthographic Projection
CRPIX1 = 256.5 / Axis 1 Reference Pixel
CRPIX2 = 512.5 / Axis 2 Reference Pixel
CRVAL1 = 255.4165453 / RA at Frame Center, J2000 (deg)
CRVAL2 = -41.98982456 / Dec at Frame Center, J2000 (deg)
CROTA2 = 0.003542484565 / Image Twist +AXIS2 W of N, J2000 (deg)
CDELT1 = -0.0002777777845 / Axis 1 Pixel Size (degs)
CDELT2 = 0.0002777777845 / Axis 2 Pixel Size (degs)
USXREF = -256.5 / U-scan X at Grid (0,0)
USYREF = -1176. / U-scan Y at Grid (0,0)
SKYVAL = 536.9782715 / GFIND Sky Estimate
SKYSIG = 3.097229004 / Grid Noise Estimate
MAGZP = 19.9642 / Calibrated zero point from CALMAN
CALID = ' y lf 0 Nov 20 2001'/ Calibration descriptors from CALMAN
SEESH = 0.9600 / Seeing shape parameter from SEEMAN
DXFS = 0.33258003 / Cross-scan Frame Step (arcsec)
DYFS = -82.39670563 / In-scan Frame Step (arcsec)
PIXNAM = 'nl.pixphot - v 011003s'
QT0227 = 535.210083 / 2.27 Percentile
QT0668 = 536.149292 / 6.68 Percentile
QT1586 = 537.1963501 / 15.86 Percentile
QT3085 = 538.486084 / 30.85 Percentile
QT5000 = 540.2935791 / 50.00 Percentile
QT6914 = 543.4226074 / 69.14 Percentile
QT8413 = 550.0908813 / 84.13 Percentile
QT9331 = 568.4039917 / 93.31 Percentile
QT9772 = 632.0999756 / 97.72 Percentile
BASE = 6 / Pixel Dwell (microsec)
WAVEF_P = '2masss.scn' / Secondary waveform data file
TIMER0 = 52 / Read1 time (millisecs)
TIMER1 = 1298 / Read2-Read1 time (millisecs)
TIMER2 = 51 / Secondary settling time (millisecs)
ICSVERSN= '990506 ' / ICS script pgm Version (yymmdd)
SCHEDVER= '990325 ' / Scheduler pgm Version (yymmdd)
SCRIPTFN= 'survey.sct' / Script template filename
SCRPTVER= '980223 ' / Script template filename Versn (yymmdd)
UT_OFF1 = 7.427007299270E-01 / UT Offset (IC),SOS to frm#1 Cntr (secs)
XS_OFF1 = 1.280000000000E+00 / X-Scan Offset (IN),SOS to f#1 RA Cntr (ASec)
IS_OFF1 = -3.653700000000E+02 / In-Scan Offset (IN),SOS to f#1 Dec
Cntr(ASec)XS_OFF2 = 1.060000000000E+00 / X-Scan Offset(IN),EOS to End Frm RA
Ctr(ASec)IS_OFF2 = 1.236100000000E+02 / In-Scan Offset(IN),EOS to End Frm
Dec Ctr(AS)FOCUS = 973 / Focus Setting
NUMFRMS = 274 / Total Number of Frames in this Scan
SKIPRDOS= 0 / Total Number of SOS junk RDOs skipped (IC)
TELNAME = 'CTIO ' / Telescope -30.165/+70.815 lat/lon degs
FILTER = 'k ' / Band: j, h, k
UT_DATE = '990812 ' / UT Date of Frame (IC) (yymmdd)
UT = '23:51:26.63' / Time of Frame (IC) (sxgsml)
AMASS_FC= 1.03087914E+00 / Airmass (aprox) at this Frame (IC)
(unitless)GRP2_SOS= 'SOS ' / Bgn Group#2 .par params at SOS
DATE_SOS= '990812 ' / Date at SOS (yymmdd)
EQUINOX = 2.000000000000E+03 / Equinox at SOS
AM_SOS = 1.02999997E+00 / Airmass at SOS (unitless)
ZD_SOS = 1.31000004E+01 / Zenith Distance at SOS (degs)
HA_SOS = '-00:29:41.00' / Hour Angle at SOS (sxgsml)
UT_SOS = '23:51:14.00' / Scan Reference UT (SOS) (sxgsml)
ST_SOS = '16:31:57.00' / Sidereal time at SOS (sxgsml)
RA_SOS = '17:01:40.33' / Scan Reference RA at SOS ,epoch 2000
(sxgsml)DEC_SOS = '-41:42:15.9' / Scan Reference Dec at SOS,epoch 2000
(sxgsml)WSPD_SOS= 0 / Wind Speed at SOS, see WARNING below
WDIR_SOS= 0 / Wind Direction at SOS, see WARNING below
HUM_SOS = 12 / Humidity at SOS, 0-100%
SEE_SOS = 0.00000000E+00 / Seeing at SOS, see WARNING below
BAR_SOS = 2.98999996E+01 / Barometer at SOS (inches of Hg)
AIRT_SOS= 1.48999996E+01 / Air temperature at SOS, degs Celsius
TELT_SOS= 1.40000000E+01 / Telescope Temp at SOS, degs Celsius
ARYT_SOS= -1.90000000E+02 / Temperature of array, see WARNING below
GRP2_EOS= 'EOS ' / Bgn Group#2 .par params at EOS
DATE_EOS= '990812 ' / Date at EOS (yymmdd)
AM_EOS = 1.05999994E+00 / Airmass at EOS (unitless)
ZD_EOS = 1.86000004E+01 / Zenith Distance at EOS (degs)
HA_EOS = '-00:22:53.00' / Hour Angle at EOS (sxgsml)
UT_EOS = '23:58:01.00' / UT at EOS (sxgsml)
ST_EOS = '16:38:45.00' / ST at EOS (sxgsml)
RA_EOS = '17:01:40.44' / RA at EOS, epoch 2000 (sxgsml)
DEC_EOS = '-48:05:13.3' / Dec at EOS, epoch 2000 (sxgsml)
WSPD_EOS= 0 / Wind Speed at SOS, see WARNING below
WDIR_EOS= 0 / Wind Direction at EOS, see WARNING below
HUM_EOS = 12 / Humidity at EOS, 0-100%
SEE_EOS = 0.00000000E+00 / Seeing at EOS, see WARNING below
BAR_EOS = 2.98999996E+01 / Barometer at EOS (inches of Hg)
AIRT_EOS= 1.46999998E+01 / Air temperature at EOS, degs Celsius
TELT_EOS= 1.38999996E+01 / Telescope Temp at EOS, degs Celsius
ARYT_EOS= -1.90000000E+02 / Temperature of array, see WARNING below
COMMENT *** WARNING *** indicated parameter not measured, dummy only
COMMENT src keys: (IK)=IPAC Konstant; (IC)=IPAC cmptd; (IN)=IPAC namelist
COMMENT (OV)=Obsrvtry .par file variable
COMMENT Group 2 parms are ALL from the Obs .par file
COMMENT non-Group 2 parms w/o (xx) are usually fm Obs
RF_NLID = 'norot sat s 980730' / Rdframe namelist version id
HISTORY * Rdframe version= 980423 jhw. Bgn Xeq = 01-11-18 13:51:38
HISTORY * DFlat vsn1.96 981203 Run on 11/18/01 at 13:50:28
HISTORY > Image Created by pixphot - Version 010925p
HISTORY > Gene Kopan IPAC/ Caltech