Instrumental Effects and their Calibration · Calibrators in radio astronomy • Astronomical calibrators — to set flux density scales, feed polarisation angle, slow-varying gains…
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Instrumental Effects and their Calibration
wasim raja
Why calibrate your instrument?
Why calibrate your instrument?
Radio telescopes measure Electric Fields
Animation Courtesy: www.best animations.com
Radio telescopes measure Electric Fields
Animation Courtesy: www.best animations.com
Radio telescopes measure Electric Fields
Animation Courtesy: www.best animations.com
Radio telescopes measure Electric Fields
Animation Courtesy: www.best animations.com
Radio telescopes measure Electric Fields
Animation Courtesy: www.best animations.com
What needs calibration?
Detector Orientation or Feed Position Angle
Feed Types
Leakages
Gains or Amplification factors
Instruments are generally moody
But often in a predictable way
• Slow variation in Time • Smooth changes across Frequency • Different response in different look-
directions. • System restarts/Power cycles can
be tricky
System variations in time and frequency
Calibration: Inadequate Cadence Higher Cadence
Calibration: Inadequate Cadence Higher Cadence
Wide-field artefacts
Wide-field artefacts
Wide-field artefacts
Need for Standards
Need for Standards
Calibrators in radio astronomy
• Astronomical calibrators — to set flux density scales, feed polarisation angle, slow-varying gains… — Time Overhead!
• Synthetic calibrators — to correct time-dependent effects, bandpass calibration — Calibration of Calibrator?
• Certain a priori information: Self-calibration
Challenges
Challenges
Challenges
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