Chapter 3:
ACS Calibration Pipeline
3.1 On The Fly Reprocessing (OTFR)
3.2 Pipeline Overview
3.2.1 CALACS: Image Calibration
3.2.2 PyDrizzle: Distortion Correction and Dither Combination
3.2.3 When is OTFR not Appropriate?
3.3 Structure of CALACS
3.4 CALACS Processing Steps
3.4.1 ACSCCD
3.4.2 ACSREJ
3.4.3 ACS2D
3.4.4 ACSSUM
3.5 Manual Recalibration of ACS Data
3.5.1 Requirements for Manual Recalibration
3.5.2 CALACS Examples
This chapter describes the ACS calibration pipeline and the On-the-Fly-Reprocessing, which is standard for all HST data requested from the STScI archive. The pipeline software consists of two separate packages: CALACS and PyDrizzle. CALACS removes various instrumental signatures, combines multiple exposures, and updates header keyword values. PyDrizzle corrects images for geometric distortion and combines observations which were taken as part of a dither pattern.
The data products from OTFR are described, as well as considerations and requirements for manual recalibration. The remaining bulk of the chapter is devoted to a detailed description of CALACS. While PyDrizzle is also used during pipeline processing, a detailed discussion of this software is deferred to Chapter 4.
