Calibrations#
Calibration products (e.g., combined bias, dark, and flat frames).
Citation: NSF-DOE Vera C. Rubin Observatory (2026); Legacy Survey of Space and Time Data Preview 2: calibrations dataset type 
<doi-tbd>
Access#
The calibration products are accessible via the Butler.
Unlike other data products, most calibrations are associated with a “validity range” as well as a Butler dataId (e.g., detector and physical_filter), since different calibrations can be valid for different observations.
This is usually best provided by also passing an exposure or visit ID when looking up a calibration in addition to the calibration’s regular data ID dimensions, since both exposure and visit are associated with a timespan in the butler database.
Butler#
Number of Butler datasets: <tbd>
Examples of dataset types:
(‘bias’, {instrument, detector}, ExposureF, isCalibration=True)
(‘dark’, {instrument, detector}, ExposureF, isCalibration=True)
(‘flat’, {band, instrument, detector, physical_filter}, ExposureF, isCalibration=True)
(‘ptc’, {instrument, detector}, PhotonTransferCurveDataset, isCalibration=True)
(‘bfk’, {instrument, detector}, BrighterFatterKernel, isCalibration=True)
Description#
The process of Instrument Signature Removal (ISR; also called “image reduction”) uses calibration products such as bias, dark, and flat field calibration frames as part of the process to transform raw images into visit images.
Bias images: An exposure obtained with zero exposure time to measure the pedestal level of counts applied during readout.
Dark frames: An exposure obtained with a nonzero exposure time but with no illumination (shutter closed) to measure the detector’s response to the thermal energy in the camera.
Flat fields: An exposure taken with even illumination across the field to measure pixel response variations.
Photon transfer curves (ptc): TBD
Brighter-fatter kernel (bfk): TBD
Processing#
The calibration frames and associated relations and kernels are created by processing calibration images and used in the Instrument signature removal (ISR) pipeline.
Pixel data#
ExposureF calibration products such as the combined bias, dark, and flat have an image plane and a variance plane.
The pixel data units are ADU (analog-to-digital units).
Metadata#
ExposureF calibration frames have a header and bounding box but don’t have a World Coordinate System (WCS) object.
Tutorials#
See the 200-level catalog Tutorials for a notebook on the calibration products.