Association Overview

What are Associations?

Associations are basically just lists of things, mostly exposures, that are somehow related. With respect to Roman Mission and the Data Management System (DMS), associations have the following characteristics:

  • Relationships between multiple exposures are captured in an association.

  • An association is a means of identifying a set of exposures that belong together and may be dependent upon one another.

  • The association concept permits exposures to be calibrated, archived, retrieved, and reprocessed as a set rather than as individual objects.

  • For each association, DMS will generate the most combined and least combined data products.

Associations and Roman

The basic chunk in which science data arrives from the observatory is termed an exposure. An exposure contains the data from detector reads that for the Roman mission are set by the MA table (Multiaccum Table). These resultants are the product transmitted to the ground and a set of these constitutes an exposure for the detector. In general, it takes many exposures to make up a single observation, and a whole program is made up of a large number of observations.

On first arrival, an exposure is termed to be at Level 0: The only transformation that has occurred is the extraction of the science data from the observatory telemetry into a ASDF file. At this point, the science exposures enter the calibration pipeline.

The pipeline consists of the ELP (Exposure Level Processing) and the HLP (High Level Processing) which together comprise three levels of data generation and processing: Level 1, Level 2, and Level 3. Level 1 data consist of uncalibrated individual exposures, containing raw pixel information, formatted into the shape of the detectors. Level 2 data have been processed to correct for instrument artifacts and have appropriate astrometric and geometric distortion information attached, and with the exception of grism data, are in units that have known scaling with flux. The resulting files contain flux and spatially calibrated data, called Level 2 data. The information contained in these files are still related to individual exposures.

In order to combine or compare exposures, the data are resampled to a regularized grid, removing the geometric distortion of the original pixels. This process creates Level 3 data.

Utilities

There are a number of utilities to create user-specific associations that are documented under Association Commands.