MultiDrizzle Status and Development Overview Anton Koekemoer, ACS+WFPC2 Branch

1. MultiDrizzle Overview - Anton Koekemoer MultiDrizzle Status and Development OverviewAnton Koekemoer, ACS+WFPC2 Branch • Project Overview • Forum: Dither Working Group • Software Development Mechanism • Development Timeline to Date • MultiDrizzle Requirements • General • Instrument-Specific Considerations • MultiDrizzle Testing • General Overview • Instrument-Specific Considerations • Priorities and Timescales • Development and Testing • Documentation • Community Feedback • Roadmap for Future Development

2. MultiDrizzle Overview - Anton Koekemoer MultiDrizzle Project Overview • Forum - Dither Working Group (established January 2002): • Purpose: • Coordinate development & implementation of fully integrated software to automatically register, CR clean and combine dithered HST images (software intended as successor to CL-based STSDAS “dither” pkg) • Process: • Provide forum for dialog between INS, SSB, and dither software users • Define requirements and set priorities for development and testing • Determine roadmap for implementation, distribution, documentation • Membership: • Representatives from INS, SSB, + others attending as needed • Development Mechanism: • MultiDrizzle requirements initially developed through discussions within Dither Working Group and interations with users • MultiDrizzle prototype (Koekemoer, Fruchter, Hook et al.) developed to demonstrate desired functionality; beta release under STSDAS • SSB redesigns the code, reproducing the functionality of prototype • Continual testing by SSB and INS, and dialog with external users

3. MultiDrizzle Overview - Anton Koekemoer MultiDrizzle Project Organization

4. MultiDrizzle Overview - Anton Koekemoer MultiDrizzle Development to Date • Jan - May 2002: • Definition of MultiDrizzle requirements in Dither Working Group • Initial prototype MultiDrizzle (Koekemoer, Fruchter, Hook et al.) • Jun - Sep 2002: • Distribute prototype to variety of GOs: GOODS, GEMS, High-Z SNe, GRBs, APPLES, Helix Nebula; external GOs at GSFC, CfA, Caltech,... • Oct - Dec 2002: • Announce general availability to GOs on beta-test basis (Cal Wkshp) • Initial suite of ACS, WFPC2 test datasets • Jan - Jun 2003: • Hand over prototype to SSB for inclusion in STSDAS (Hack et al.) • More user feedback, improve robustness, refine testing • Jul 2003 to present: • SSB redesign of MultiDrizzle code (Hack, Hanley et al.) using prototype MultiDrizzle as a basis for defining functionality • Develop formal regression test suites

5. MultiDrizzle Overview - Anton Koekemoer MultiDrizzle Requirements - General • Fundamental Requirements: • Combine arbitrary collections of images (including single-group) • Automatically calculate required output image size • Determine shifts from headers • [Optionally refine shifts or allow input delta-shifts] • Carry out sky subtraction on input images • Automatically perform CR rejection: • Drizzle input exposures onto separate, registered output images • Create a clean “median” image • Blot the clean image back to frame of each individual exposure • Run deriv, driz_cr to create cosmic ray masks • Use CR masks in final drizzle combination • Allow external bad-pixel masks to be imported • Allow individual steps to be selected when running • Overall philosophy: • Allow user freedom in specifying behavior via parameters • Defaults must enable good results from “one-touch” operation

6. MultiDrizzle Overview - Anton Koekemoer Requirements – Instrument-Specific • ACS • Accurately handle WFC, HRC, SBC imaging data • Single-group images (eg only [sci,1]) • Sub-array data • Include new geometric distortion-residual images (Anderson) • WFPC2 • Handle 4-group WFPC2 GEIS as well as FITS format files • Single-group images (eg WF3 only) • Sub-array data • Include updated geometric distortion (Platais et al) • NICMOS • NIC1, NIC2 or NIC3 imaging • Ability to handle multi-accum datasets • STIS • CCD as well as FUV, NUV-MAMA datasets • Imaging (initially) as well as 2d spectroscopy data (later)

7. MultiDrizzle Overview - Anton Koekemoer MultiDrizzle Testing- General Overview • Basic Functionality: • Do new versions run successfully for small subset of test datasets? • Extended functionality: • Do new versions work for the full range of datasets? • Functionality tests can be automated by regression: • Run automatically on a periodic basis • Comparison performed automatically with reference test images, and results reported in summary form • Scientific integrity: • Do functional versions deliver scientifically valid results? • Different target types: • Sparse extra-galactic fields, crowded stellar fields • Large extended objects or diffuse emission across entire field • Scientific tests require additional analysis, eg: • PSF measurements of stars to ensure shifts, etc are correct • x,y position comparisons to verify correct astrometry

8. MultiDrizzle Overview - Anton Koekemoer Testing – ACS + WFPC2 • ACS WFC, HRC, + WFPC2: • Basic datasets: • 2-point line dither • 4-point box dither (single-visit) • More advanced datasets: • Single-visit, small offsets, higher number of dithers • Single-visit, large offsets (comparable to chip size) • Multi-visit, small + large offsets • Number of images: • Small datasets (2-3 exposures total) • Medium datasets (4-6 exposures total) • Large datasets • ACS testing lead: Shireen Gonzaga • WFPC2 testing lead: Vera Platais

9. MultiDrizzle Overview - Anton Koekemoer Testing (cont’d) - NICMOS, STIS • NICMOS: • Imaging - NIC1, NIC2, NIC3: • Multi-accum datasets • Different dither patterns (spiral) • Large-scale + small-scale dithers to account for chip defects • NICMOS testing lead: Megan Sosey • STIS CCD + MAMAs: • Imaging: • Mostly large-scale dithering • Spectroscopy: • Dithering along slit • Dithering along spectral direction • CTE: CRs, bad pixels are a major issue (since low background) • STIS testing lead: Linda Dressel

10. MultiDrizzle Overview - Anton Koekemoer Priorities and Timescales • Development and Testing: • Near-term (+ 1 month): • INS: Identify test datasets and create baseline results • SSB: Include tests in regression mechanisms • SSB: upgrade current beta-release MultiDrizzle to fully supported • Long-term: • Maintain database of reference results • Update test database when warranted by code changes • SSB release redesigned MultiDrizzle: for users and HST pipeline • Documentation: • Release TIR describing development plans for MultiDrizzle • Release updated Dither Handbook V3.0 to user community, with full description of the use of MultiDrizzle • Community Feedback: • Continue to collect suggestions and feedback from users • Incorporate into regular prioritization planning

11. MultiDrizzle Overview - Anton Koekemoer Proposed Roadmap for Future Development • Mar 2004: • SSB to upgrade original “prototype” MultiDrizzle to a fully supported version (eg via patch release, and/or from STSDAS website) • INS to release updated Dither Handbook V3.0 with full description of the use of MultiDrizzle software • Jan - Jun 2004: • INS provide test datasets to SSB (near-term), update as necessary • SSB to complete the redesigned MultiDrizzle as user software • SSB to release redesigned MultiDrizzle in Summer 2004 STSDAS • Jul - Sep 2004: • SSB, INS work on more robust, streamlined MultiDrizzle for fully automated use in HST Pipeline Operations • Continue to incorporate feedback and usage patterns from GOs • Oct 2004 onwards: • Continuing algorithmic development to improve software, eg: • tweakshift (automated catalog-based shift refinement) • more robust CR rejection techniques for few-exposure datasets