Coronagraph Instrument Data
The Coronagraph Instrument, designed and built at the Jet Propulsion Laboratory (JPL) in Pasadena, California, has a nominal allocation of three months of observing time for the technology demonstration during the initial 1.5 years of the Roman Space Telescope primary mission. This document covers the elements of the Coronagraph instrument operations and technology demonstration that are the responsibility of the Coronagraph Operations Support (COS) and Coronagraph Data Management System (CDMS), with introductions to other elements (e.g. the elements and data taking modes of the coronagraph) as appropriate to understand the functions.
Coronagraph Data Management System (CDMS)
The Roman ground stations are responsible for capturing telemetry from the spacecraft science recorder and a housekeeping (HK) recorder. The science recorder captures all science observation (image) data along with “unfiltered” (sampled as produced) instrument and spacecraft telemetry, while the HK recorder contains instrument and spacecraft telemetry sampled more coarsely to allow faster download.
The science recorder data stream contains all astronomical target data from EXCAM and the Low Order Wavefront Sensor (LOWFS) data, as well as other coronagraph telemetry, at an unfiltered cadence. As with data from the HK recorders, these data are in raw packetized (level 0) form. However, the science recorder data will be downlinked from the spacecraft through the ground station to the DAPHNE cloud. The data will then flow to the Science Operations Center (SOC) and then to the Science Support Center (SSC) via the NASA Mission Cloud Platform. All coronagraph data will be stored in the data analysis environment (DAE) maintained by the SSC for higher-level data processing. Each of the types of higher processed data (L1-L4) will be transferred back to the Roman archive. This data flow is shown below. The SSC is also responsible for delivering all coronagraph Integration and Test (I&T) and commissioning data to the SOC for archiving.
Figure 1: Illustration of the coronagraph data flow from the science recorder during nominal operations. Level-0 CGI data flow from the spacecraft to SSC via the Roman Ground System. The SSC processes L0 data, and also delivers higher level coronagraph data (L1-L4), ancillary data and calibration reference files, to the SOC. The Coronagraph Technology Center (CTC) and Community Participation Program (CPP) are shown partially within the SSC box because it is expected that much of the higher level CGI data processing will occur within the data analysis environment (DAE) on premises at SSC.
Data Processing Level
The primary astronomical observation data from the coronagraph instrument will be taken with its EXoplanetary systems Camera (EXCAM). The coronagraph data levels are defined from Level 0 to 4. The Level 0 EXCAM data are raw packetized “telemetry” files received from either the MOC (in the case of HOWFSC) or the SOC at the SSC. The CDMS processes these data to Level 1 (raw, uncalibrated images, with a metadata header). These data are stored in the Data Analysis Environment for CTC and CPP to process to Level 2 (calibrated images), Level 3 (photometry, astrometric, and wavelength corrected images), and Level 4 (PSF subtraction and spectral extraction).
Ancillary Technology Demonstration Data Products and Calibration Reference Files
In general, all raw coronagraph instrument telemetry necessary for data reduction will be processed to a machine- or human-readable format by the SSC. All official data products will be validated by the CDMS and sent to the SOC for archiving. Much ancillary (non-image) coronagraph telemetry will be included in the L1 image data headers. Some ancillary data will be further processed by the CTC and CPP. The ancillary data and telemetry include:
Data from mechanisms and camera settings
Status from each wavefront control system at the time of the observation
Calibrations generated autonomously on board
Subset of housekeeping data on the science recorder
Low-order Camera (LOCAM) images
- Deformable Mirror settings
Calibration reference files will also be generated from observational and/or modelling data by the CTC. These files may include, but are not limited to:
- Flat fields
- Darks
- Bad pixel maps
Astrometric calibration files (including pixel scale solution, distortion correction, satellite spot calibration, etc.)
Photometric calibration files (including flux conversion file, etc.)
Instrumental polarization calibration files
A limited set of calibration files generated on the ground will be sent up to the spacecraft for use during coronagraph instrument observations. The data are created by the CTC and uploaded by the MOC. Currently, the flat fields are the only image files anticipated to be needed for on-board calibration.