FITS Assembler

Table of Contents:

sub-FITS

• sub-FITS are FITS files containing images or data (or both) and are created by subsystems throughout KPF

• Some are created by devices (i.e. Archons) and some by dispatchers (i.e. Ca HK Detector dispatcher)

• Each sub-FITS is designed to be stand-alone, and contain all of the relevant subsystem information within

• The sub-FITS are assembled together by the FITS Assembler to form a single FITS file per observation

L0 FITS Format

As per Data Format, the post-observation 'Level 0' (L0) format expected by the DRP is:

• There is one L0 FITS per observation

• It contains all of the raw data from the observation

• Within HDU 1 it also contains header data from the overall system (i.e. telescope and observatory) that is not contained within the sub-FITS headers

obsID

The KPF “Observation ID” (obsID) is utilized to ensure that the appropriate images and data are assembled together into the correct L0 FITS.

The rationale is to prevent images/data from an observation being combined with images/data from the next observation. This could happen at the end of an exposure, when the images are being read out from the CCD but the system is changing or preparing for the next exposure.

The obsID will be stored in a keyword. It will be an integer that is incremented at the start of each new KPF observation/exposure.

Each subsystem will take this obsID and:

• use it within the sub-FITS filenames (“subsystem-prefix_obsID.FITS”)

  • this allows for straightforward assembly of correct files, and the assembler only needs to look at filenames

• place it within the header of each sub-FITS

  • maintains obsID traceability after the L0 is created and the sub-FITS filenames are lost

Directory Structure for FITS Files

• Proposed directory structure for KPF:

kpf-asl-prime → KPF FITS Main Directory → L0 FITS Directory

→ Sub-FITS Directory → Green

→ Red

→ Ca_HK

→ ExpMeter

→ Guidecam

→ Solar_Irrad

• The sub-FITS sub-directories will hold the separate FITS from each subsystem before L0 assembly

• The sub-FITS will not be immediately deleted after L0 assembly, but will remain in the directory for one month (TBC) as a backup

Final L0 Filename

As per KPF File Names, the L0 Filename expected by the DRP is:

Assembly

• After each observation, the FITS Assembler pulls images with the appropriate obsIDs from the separate subsystem interim directories

• These sub-FITS are then directly copied into the larger L0 FITS, in the correct order, with no modifications