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 will provide a facility for creating mosaic frames.
For even more detailed information on what operations were performed on the data, see the [LINK: VBI repository ReadTheDocs information].
TODO:
Add link to VBI ReadTheDocs information