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Auxiliary data

Similar to CE interferometers, VLBI uses a large number of associated data sets for calibration and data flagging. VLBI is different in the sense that this information is not always availableapplied during correlation and needs to be appended to the data product. Below we list a number of such data sets that possibly need to be read from external sources. Because it can not be anticipated beforehand which calibration method will be used for a certain project (e.g. which ionospheric model), this requires in some sense that the Measurement Set can be flexibly extended.

Examples are:

• meteorological data (e.g. for tropospheric correction)

• GPS timing data

• phase calibration data based on pulse cal detection at telescope or correlator

• amplitude calibration based on state count statistics

• ionospheric data of various sources (e.g. TEC monitoring)

• accurate total power measurements to monitor phase excursions for mm VLBI

• specific data associated with record and playback processes

• for Space VLBI additional information will be carried along with the data (e.g. satellite parallactic angle, sensitivity, orbit, downlink information, ``delta-t'' tables etc.), and tasks to read, process and apply corrections based on these data will be required