FREQ_OFFSET Frequency offset information.

Name

Format

Units

Measure

Comments

Columns

Key

ANTENNA_ID

Int Antenna identifier

FEED_ID

Int Feed identifier

SPECTRAL_WINDOW_ID

Int SPECTRAL_WINDOW_ID

TIME

Double s EPOCH Time interval mid-point

INTERVAL

Double s INTERVAL

Data

OFFSET

Double Hz Frequency offset

Notes: The table contains frequency offset information to be added directly to the defined frequency labeling in the SPECTRAL_WINDOW sub-table as a Measure offset. This allows bands with small time-variable, ad hoc frequency offsets to be labelled as the same SPECTRAL_WINDOW_ID, and calibrated together if required.
This table may also be useful for fine tuning in the definition of the spectral windows for the radiometers as small frequency offsets may be present from one such device to an other. However it may be necessary to use a more general solution by defining one spectral window for each radiometer in case there is not only a global offset from one device to an other.
Note that the offsets when using the frequency switch observing mode must not be set in this table; they are defined in the SWITCH_CYCLE table.
ANTENNA_ID
Antenna identifier, as indexed in the ANTENNA_ARRAY collection in the CONFIG_DESCRIPTION table.
Note that if there is an offset antenna independent, e.g. in case the frequency switch observing mode is used, a value of -1 can be used for ANTENNA_ID. In case there is simultaneously an antenna-based offset and a global antenna independent offset the actual offset will be be considered as the sum of both.
FEED_ID
Feed identifier, as indexed from FEED  in the FEED_LIST collection in the CONFIG_DESCRIPTION table.
SPECTRAL_WINDOW_ID
Spectral window identifier
TIME
Mid-point of the time interval over which the data in the row are valid. Require to use the same TIME Measure reference as in MAIN
Note that in case the offset is for observations in Frequency Switch mode, the pair of keys TIME,INTERVAL is irelevant.
INTERVAL
Time interval.
In case the offset is for observations in Frequency Switch mode, INTERVAL corresponds to the duration of the step in the switching cycle Note that in case the offset is for observations in Frequency Switch mode, the pair of keys TIME,INTERVAL is irelevant.
OFFSET
Frequency offset to be labelled to the frequency axis for this spectral window, as defined in the SPECTRAL_WINDOW sub-table. Required to have the same Frequency Measure reference as CHAN_FREQ  in that table.

Remark:
In the MeasurementSet ( MSv2.0) this table is baseline-based to support various peculiarities of practice in Doppler tracking, especially in VLBI. In that context it has also a FIELD_ID attribute. This level of generality is not required for the AEDF.