Table 21.3 summarises the properties of the atmosphere and the resulting noise (including also the instrumentation) at both wavelengths.
Item | Radio mm | Optical |
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0.6mm to 1cm | 0.4 to 30 ![]() |
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30 to 450 GHz | 10 to 600 THz |
Comparison given for |
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Noise sources | background limited | photon limited |
(gaussian) | (poisson)![]() |
|
Main instrumental noise | Receiver (thermal) | Detector (read-out) |
thermal sky emission | ||
Signal Detection |
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photon limited |
Seeing origin | Variation of W(H![]() |
Variation of ![]() |
Fried
Parameter ![]() |
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(size of the coherence cell) | ||
Coherence Time ![]() |
several 10 minutes | ![]() |
(time to reach
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||
Equivalent to | Single-speckle | Multi-speckle |
Atmospheric correction | ||
Photometry | monitoring of T![]() |
``standard'' photometry technics |
Seeing | radiometric | tip tilt |
phase correction | adaptive optics | |
Phase Calibration | phase referenced | ![]() |
on nearby sources | closure phase on dual interferometer | |
Measurements | complex correlator rates:
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complex visibility ![]() |
fringe contrast | |
Information on |
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Imaging | Complex visibilities | Phase retrieval by |
closure relations | ||
Algorithms | all standard imaging | + amplitude model fitting |
in the UV plane |