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:. Currently the speckle reconstruction is occurring in Boulder rather than at the telescope. Once speckle reconstructed, data will be re-ingested into the data center for conversion to Level 1 science data. For any data that cannot be speckle reconstructed, the basic calibration flow below will be followed. For any speckle reconstructed data, Level 0 (raw) data will never be available.
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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. |
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