• HighFrequencyData

Dealing with high-frequency data

F. Gueth

• Existing & future instruments

  • PdBI, SMA, CARMA, ALMA
  • Frequencies involved (mm to submm)
  • Angular resolution involved
• Main issues compared to cm interferometry
  • The atmosphere: aborption, phase fluctuations
  • Low SNR
• Observing modes
  • Heterodyne receivers in the mm/submm domain
  • Spectral line observations: standard, with hundreds/thousands of channels
  • Polarization: not yet standard, but coming soon
  • Calibrators: quasars (but usually weak and variable)
• The atmosphere at mm/submm wavelengths
  • absorption
  • phase fluctuations
  • amplitude decorrelation
• Calibration of the atmospheric absorption
  • "chopper-wheel" technique
• Calibration of the atmospheric phase noise
  • principles
  • 22 GHz or 183 GHz radiometers
• Off-line data calibration
  • bandpass
  • long-term phase fluctuations
  • flux scale
  • long-term amplitude fluctuations
• Imaging
  • techniques similar to cm interferometry
  • ... but easier: less pixels, smaller fields of view
• Data analysis
  • Dealing with data cubes: vizualization along spatial and velocity axes
  • Dealing with noise: doing science at 3 sigma