This document provides an overview of the steps used to calibrate data from the VBI instrument to Level 1 FITS files. The VBI instrument is unique in that most of the processing is done at the telescope rather than the Data Center. See https://nso.edu/telescopes/dkist/instruments/vbi/ for an overview of the VBI instrument. The VBI calibrations steps are summarized as follows in Figure 1 and are described in detail in the table below:
Calibration Operations | Description |
|---|---|
Dark Correction | Remove dark current signal using Dark Calibration parameters. As part of this, check that Dark Calibration matches relevant data parameters. Extrapolate an existing Dark Calibration to a new exposure time under the assumption of detector linearity, if necessary. Verify that the dark calibration meets a minimum quality threshold. |
Gain Correction | Correct data for non-linear response using Gain Calibration parameters. As part of this, check that Gain Calibration matches relevant data parameters. Test that gain data is a consistent set. Normalize gain calibration to have unity mean. Verify that the gain calibration meets a minimum quality threshold. |
Target Correction | Make sure camera layout and position match and apply Target Calibration World Coordinate System (WCS) offsets to science Metadata making sure the metadata is precise. |
Validate Science Data | Check that all frames in science data come from the same data set parameters. |
Speckle Reconstruction | Use speckle reconstruction to algorithmically removing the degradation of image quality due to the influence of Earth's turbulent atmosphere. Using the reconstruction algorithms, the information contained in a series (80-100) of short exposed images freezing the atmospheric aberrations is used to compute a single reconstruction at high spatial resolution. See https://ui.adsabs.harvard.edu/abs/2012SPIE.8451E..1CW/abstract for more details. |
Generate Science Data | Convert to Level 1 science data using SPEC-0214. At the Data Center the metadata in the calibrated frames will be updated to be SPEC-0214-compliant in step with calibrated data from other instruments. |
Note that field sampled data will not automatically be turned into mosaiced frames so as to provide data to the user that has not been interpolated. The User Tools https://docs.dkist.nso.edu/projects/python-tools/en/latest/ will provide a facility for creating mosaic frames.
For even more detailed information on what operations were performed on the data, see the https://docs.dkist.nso.edu/projects/vbi/en/stable/index.html.