Post on 08-Jan-2016
description
+
AstroDrizzle Products for HST & JWST
2014 STScI Calibration WorkshopJennifer Mack, STScI
+ AstroDrizzle
Part of the DrizzlePac software package,
a suite of tasks for aligning & combining images
July 2012: AstroDrizzle replaced MultiDrizzle in the pipeline
More accurate handling of image distortion Resolves astrometric errors in prior pipeline products ~1-3 pixels Only AstroDrizzle supports the latest distortion corrections
+ Distortion
--> imheader *flc.fits[1] l+
IDCTAB = 'jref$v8q1444sj_idc.fits'CTYPE1 = 'RA---TAN-SIP' CTYPE2 = 'DEC--TAN-SIP' CRPIX1 = 2048.0 CRPIX2 = 1024.0 CRVAL1 = 3.570976354857465 CRVAL2 = -30.40853421183697 CD1_1 = -1.2368663915761E-05 CD1_2 = 5.40792001738662E-06 CD2_1 = 6.22592168300775E-06 CD2_2 = 1.28863357087715E-05
A_ORDER = 4 B_ORDER = 4A_0_2 = 2.15855556719611E-06 B_0_2 = -7.2205055908409E-06A_1_1 = -5.1799259715535E-06 B_1_1 = 6.18651663667832E-06A_2_0 = 8.54735349534391E-06 B_2_0 = -1.7316236718108E-06A_0_3 = 9.48132134575003E-12 B_0_3 = -4.0744859582615E-10A_1_2 = -5.2350450605432E-10 B_1_2 = -6.7147082489847E-11A_2_1 = -4.4750751791397E-11 B_2_1 = -5.0664045452596E-10A_3_0 = -4.7306614567992E-10 B_3_0 = 8.84394906333280E-11A_0_4 = 1.31172591483522E-14 B_0_4 = -9.8894110757065E-15A_1_3 = -2.3901889495070E-14 B_1_3 = 1.26720582177971E-14A_2_2 = 3.79343576547842E-14 B_2_2 = -3.7703000929016E-14A_3_1 = 3.81170188644090E-16 B_3_1 = -3.1721984142757E-15A_4_0 = 2.32007544572055E-14 B_4_0 = -1.8758253622538E-14
Linear Terms: CD MatrixNon-Linear Terms: 4th order polynomial solution uses SIP convention
Meurer et al. 2002 HST Cal Wkshp
+
--
> catfits *flc.fits
EXT# FITSNAME FILENAME EXT DIMENSION
0 jb5g08z2q jb5g08z2q_flc
1 IMAGE SCI 1 4096x2048
2 IMAGE ERR 1 4096x2048
3 IMAGE DQ 1 4096x2048
4 IMAGE SCI 2 4096x2048
5 IMAGE ERR 2 4096x2048
6 IMAGE DQ 2 4096x2048
7 IMAGE D2IMARR 1 4096x1
8 IMAGE D2IMARR 2 4096x1
9 IMAGE WCSDVAR 1 65x33
10 IMAGE WCSDVARR 2 65x33
11 IMAGE WCSDVARR 3 65x33
12 IMAGE WCSDVARR 4 65x33
Non-polynomial lookup tables in new FITS extensions
Distortion
‘Detector to Image’ correction WFC3/UVIS lithographic mask pattern ACS/WFC column width correction
Filter-residual lookup tables (DGEOFILE)
Kozhurina-Platais et al. WFC3 ISR 2013-04
+ Pipeline Products
Drizzled data products for ‘singles’ and ‘associations’
Image associations are at the ‘visit level’ only
1.) Defined by the user at Phase II via PATTERNs, CR-SPLITs, RPT-OBS
e.g. IR-BLOB-DITHER, UVIS-DITHER-BOX
2.) Additional rules defined by the instrument teams e.g. WFC3 images in same visit & filter
+
MAST products use default AstroDrizzle parameters for general use
Defined in MDRIZTAB reference file One MDRIZTAB per detector Rows select for number of input frames
N=1,2,6 ACS/WFC, WFC3/UVIS
N=1,2,4 WFC3/IR
Pipeline Products
+ Multi-Visit Programs
TweakReg not run in OPUS visit-level DRZ products only Strongly recommend updating the header WCS before combining
Typical HST pointing (with fine-lock on 2 guide stars)
Observing Scenerio RMS Precision .
(mas) (UVIS pix)Same orbit (dither < 1”) 2-5
0.1 Re-acq for orbits in same visit 5-20
0.1-0.4Diff visits, same guide stars, same orient 50-1001.2-2.5Diff guide stars 200-500 5.0-12.5
+ Why reprocess?
Fine-tune alignment (cross-visit, cross-filter, cross-detector)
Match sky background (reduced correlated noise, better
CRREJ)
Select bad pixel flags
Improve CR rejection
Stack many visits; build mosaics
Optimize final scale/pixfrac (PSF resampling)
+ Single Exposures
Drizzling resamples the PSF Redistributes flux onto uniform output grid Corrects distortion Convolves with mathematical kernel
Result: Blurs PSF slightly; adds correlated noiseFor N=1, users may prefer to use FLT*PAM for photometry
Else tell drizzling software to ignore DQ flags set in CALxxx pipeline
+ N=1: DRZ photometry of singles
Frame Flux (e-/s) Mag
flt1 * pam 140210 12.13
flt2 * pam 140028 12.13
drz1 139883 12.14
drz2 136512 12.16
drz1 no_dq 140285 12.13
drz2 no_dq 140138 12.13
WFC3 UVISAstroDrizzle rejects hot pixelsDQ flag =16
Dither 1Dither 2
Hot Pixels
1% low3% low
+
Ignore hot pixel Reject hot pixel
N=1: DRZ photometry of singles
+
Relative photometry of 47 TucACS ISR 2007-02 (Mack et al.)
Ignore DQ flags(treat all pixels as ‘good’)
Use DQ flags(treat flagged pixels as ‘bad’)
Delta mag Delta mag
mag
N=1: DRZ photometry of singles
+
UVIS-DITHER-LINE (2.5 pix in x & y)FLT*PAM, aperture photometry r=10 pix
# asn_ID (xc, yc) Peak (e-) Flux (e-) Mag FWHM im1 ic5pa1060 (0.6,0.6) 34331 267101 11.43 2.1 pixim2 (0.0,0.0) 47900 264994 11.44 1.5 pix
40%<1%
N=2: Intra-pixel centering
+• Star at corner vs center of pixel• Core of sharper PSF flagged as CR• Replaced with core from broader PSF• Result: Photometry 4% too low in combined image
driz_cr_scale= 1.2, 0.7
X,Y = (0.6,0.6) FWHM= 2.1 pixPeak = 35 Ke-
X,Y = (0.0,0.0) FWHM= 1.5 pixPeak = 48 Ke-
FLT
DQ
DRZ
WHT
N=2: Intra-pixel centering
driz_cr_scale= 2.0, 1.5
driz_cr_scale= 3.0, 2.5
+ N=3+ exposures
For dither patterns which optimally sample the PSFShrinking the ‘pixfrac’ can sharpen the image
Pipeline defaults ACS/WFC, WFC3/UVIS: Pixfrac = 1.0 for N < 6 WFC3/IR: Pixfrac = 1.0
Red: pixfrac = 1Blue: pixfrac < 1
Pixfrac =‘drop’ size relative to input pixel
+ Final Scale/ Pixfrac
FWHM = 0.19”Scale = 0.128”Pixfrac = 1.0
Pipeline Product
X (pix)
Y (
pix
)
IR-DITHER-BOX-MIN
WFC3-IR-DITHER-BOX-MIN Provides optimal 4-step sampling of the PSF.
+
Optimized Product
X (pix)
Y (
pix
)
IR-DITHER-BOX-MIN
FWHM = 0.18”Scale = 0.064”Pixfrac = 0.8
WFC3-IR-DITHER-BOX-MIN Provides optimal 4-step sampling of the PSF.
Final Scale/ Pixfrac
+ Sky Subtraction
localmin matchmin+match
Note: When sky not matched Poor cr-rejection & photometry; correlated noise
Large dithers changes the ‘scene’ True background may be difficult to determine for extended sources
Solution: 1.) Provide user-determined background values via ‘skyfile’ 2.) Try new sky matching in DrizzlePac 2.0
(Uses only pixels in common between exposures)
+ Release History
June 2012: v1.0
Sept 2013: v1.1.12
Corrects 2-D lithographic pattern for WFC3/UVIS data (Kozhurina-Platais et al. WFC3 ISR 2013-04)
Jan 2014: v1.1.16
Currently in MAST
Available via Ureka http://ssb.stsci.edu/ureka
Aug 4, 2014: v2.0.0
Available only as Ureka development version (SSBX)
Supports *new* ACS time-dependent distortion (Kozhurina-Platais et al., ACS ISR in prep)
New sky matching Align 2 detectors in 1 step New iterative solutions for aligning mosaics Improved source matching when CR’s dominate point
sources
+ ‘Enhancing the Past, Maximizing the Present…’
Development in progress:
Improved MAST products via new MDRIZTAB defaults
Add rows for # input frames Currently n=1,2,6; Add n=2,3,4,5
Add rows for patterns IR-BLOB-DITHER, UVIS-DITHER-BOX
Add columns for new parameters
Improved software
TweakReg: Weight sources by brightness
TweakReg: Support full 6-parameter solution to remove skew
AstroDrizzle: Parallelize all steps to improve run times
+‘…Preparing for the Future’
MAST supports Headerlet files
Small FITS files representing a single WCS solution AstroDrizzle supports multiple solutions (WCSNAME)
Eg: GAIA absolute reference frame
+ New Drizzling Forum
http://forum.stsci.edu/
New way of communicating with users
Allows more dynamic information flow
Ideal to support v2.0 software release (Aug 2014)
Open discussion develops a ‘community’ of drizzlers
To go live by end-Aug
+
DrizzlePac development for JWST is in early stages
Associations HST: at visit level JWST: by proposal, target, detector, filter
TweakReg will be run in the pipeline for multi-visit programs
Drizzled products will continually evolve to include all exposures to date
Multi-epoch associations will allow for improved CR-rejection
As for HST, headerlets can provide alignment to absolute reference frame
JWST..
+ JWST..
Distortion Same WCS keywords (linear terms in CD-Matrix) Higher order distortion in separate extension
Support different FITS format than HST MIRI, NIRSPEC IFU’s will have 3D drizzled products
(science array=3D cube in RA, Dec, lambda)
NIRSPEC – 2 options for users (drizzle all frames together, then extract spectrum) (drizzle singles, extract spectra, then coadd)
NIRCAM, NIRISS slitless spectroscopy handled similar to ACS,WFC3 grisms
For more info: Howard Bushouse (Calibration pipeline)Warren Hack
(DrizzlePac)
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