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Key concepts

The following is a list of common terms used in the radio astronomy domain. Key concepts that form the ubiquitous language for starbox have links with further details. This is a living document and will be updated as code is added.

Observations

  • Observation
  • Scan: A contiguous time interval during which the telescope observes a single field with fixed pointing.
  • Calibrator: A source observed primarily to estimate instrumental or propagation effects.
  • Target: A source or field observed for scientific analysis.

Pointing

  • Pointing
  • Right ascension
  • Declination
  • Hour angle
  • Integration time
  • Phase centre

Sky and signals

  • Polarization
  • Faraday rotation
  • RFI
  • [Sources]: sources of radio emission in a sky model or image.
    • Point source
    • Extended source (extended emission or gaussian blob)
  • Sky model (source catalog, source list)
  • Apparent sky: The sky brightness distribution as modified by instrumental and propagation effects.
  • True sky: The intrinsic sky brightness distribution, independent of the instrument.
  • Patches: Groups of sky model components treated together, typically for direction-dependent calibration.

Modes

  • Wideband
  • Widefield
  • Drift scan

Units & quantities

  • Jansky
  • Flux density (flux, intensity or brightness)

Coordinates & axes

  • Direction cosines (l,m,n)
  • Baseline coordinates (u,v,w)

Telescope

  • Telescope (interferometer, array, sub-array, station, sub-station)
  • Antenna (receptor, receiver)
  • Aperture

Array configuration

Interferometry

  • VLBI
  • Aperture synthesis
  • Fringes
  • Correlator
  • Delay

Data processing

Beam

  • Beam model (primary beam)
  • Beam forming
  • Tied-array beam forming
  • Side lobes

Calibration

  • Calibration solution (solution): An estimated set of parameters that can be applied to visibilities to correct for corruptions introduced by the hardware, electronics, atmosphere or thermal noise.
  • Reference antenna: A station used to fix phase and amplitude degeneracies during calibration.
  • Calibration: The process of estimating and applying calibration solutions.
  • Jones matrix
  • Solver: The algorithm used to estimate calibration solutions.
  • Predict: The process of predicting ideal visibilities from sky model components.
  • Self-calibration cycle: An iterative loop of imaging, model update, and calibration.

Modes

  • Phase-only
  • Amplitude and phase
  • Direction-independent
  • Direction-dependent
  • Self-calibration (self-calibration cycle)

Gains

Effects

  • Corruptions
    • Phase screen (TEC screen)
    • Bandpass
    • Delay
    • Direction-dependent effect (DDE)

Control

  • Flagging
  • Reference antenna

Imaging

Modes

  • Continuum imaging
  • Spectral imaging

Data products

  • Artifacts
  • Images
    • Dirty image
    • Residual image
    • Clean image (restored image)
    • Model image
  • Image cube: one image per frequency channel stacked together.
  • Spectral index map

Quality Metrics

  • SNR
  • Dynamic range

Wide-field

  • Facet
  • Sector
  • Field
  • W-term

Polarization

  • Stokes parameters (I, Q, U, V)

Deconvolution

Concepts

  • Image plane (image space, pixel space)
  • Visibility plane (visibility space, Fourier space)

Data formats

  • Measurement set
  • FITS file
  • CASA table
  • h5parm

Algorithms