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
