Calibration Strategy PDR
Scope of Review
• To assess plans for ALMA Calibration
• To plan for construction phase activities
• Not to include polarization calibration at this time
• Amplitude: receiver, absolute flux, bandpass, primary beam, pointing and focus, VLBI
• Phase: Fast switching and WVR correction, transfer between frequencies, infrared correction
• Atmospheric monitoring: as above, including telescope-independent measuring devices
• Review of existing facilities and research efforts
• Next steps
Scope of ALMA
• Frequency bands from 31.3 to 950 GHz
• 64 12m antennas plus perhaps 12 7m antennas
• Chajnantor site
Calibration Goals
Committee Comments
• An end-to-end description of the calibration system should be pursued vigorously
• Attention to detail is required in the long run; approaches involving sophisticated modeling may fail to 
note or solve difficult problems.  It is important to prototype as much of the system as possible, 
preferaby in an environment which is as similar to Atacama as possible.
• A coordinated Calibration Group is needed to direct and assess efforts.
– Core members: system, receiver and science groups
• SSR should work in close collaboration with Calibration Group
• The committee endorses the ASAC recommendation of 1% calibration in the millimeter regime but 
suggests 3% is more realistic in the submillimeter.

Details
• Standard gain horn approach presented by Welch endorsed for further study at BIMA, to be migrated 
onto ALMA
• Semi-transparent vane system needs resources for investigation; dual load system needs further study
• Extension of 22 GHz experiments to 183 GHz is urgent.  Simulations should be performed to guide 
studies. Details of IRMA implementation remain unclear; it may be useful as a seeing monitor
• Photonic system needs to be demonstrated in the field; interaction with other systems a concern.
• Single antenna calibration should be addressed more thoroughly

Details (continued)
• Atmospheric modeling shows good progress.  A standalone FTS at array center may usefully 
supplement WVR data when particulate ice present.  A 60 GHz temperature sounder is an effective off-
the-shelf item for inclusion in weather station.
• Pointing calibration well in hand; guide star pointing is promising and needs investigation
• Polarization calibration was deferred until further details of the photonic system are known.
Action Items
• Receiver calibration needs engineering realization.  Materials need to be identified for vane calibration and 
incorporated into a working system.  Dual load system tests should address standing waves and frequency 
dependence of the system.
• Calibration Group should be formed and design should be iterated among its members.  Prototype receivers must be 
built to push the system toward a final design.
• Characterization of standing wave patterns on the prototype antennas should be performed and assessed.
• The WVR and fast switching schemes need further work.  WVR schemes are not in production mode operation at 
22 GHz.  The combination of these techniques and rules for implementation are ill-defined.
• Anomalous refaction on the site needs characterization, perhaps with ASTE