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Flagging (UV_FLAG, RUN UV_MFLAG, RUN UV_CLIP)

The experience shows that flagging out PdBI data inside MAPPING rarely improve the results. This is the consequence of several factors: 1) The on-line PdBI system quite efficiently catch possible observations problems (e.g. phase unlock); 2) A particular care has been taken in the computation of the relative weights so that data taken in poor observing conditions will almost not affect the result. Finally, it is extremely difficult to flag data based on the data itself and a $uv$ table is an extremely compact data format which has lost most of the information needed to make intelligent flagging. This is why we recommend the use of tools like the ``quality assessment tool'' in CLIC which selects good on-source data based on observing conditions (e.g. weather, tracking, ...). This said, MAPPING offers several tools to enable data flagging in the few cases where it can be useful like the presence of a single clearly outlier visibility.

UV_FLAG command
Display $uv$ data (controled by similar variables than GO UVALL) and calls the cursor to interactively select a region where $uv$ data will be flagged. The data are flagged by changing the sign of the weight. Subsequent mapping with UV_MAP will ignore flagged data. The flagged UV table can be saved on a file with command WRITE UV File. The /RESET option can be used to unflag the data (all the flagged data, not interactive).
UV_FLAG task
Flag or unflag a specified time range in a $uv$ data set, for one or all baselines and a specified channel range. HOW CAN WE SEE EASILY THE TIME ?
UV_CLIP task
Clip $uv$ data with amplitudes higher than a given threshold. For spectroscopic data, all channels are flagged if any channel between the first and last considered has an amplitude greater than the trheshold. Clipped channels are set to zero amplitude and zero weight. It doesn't seem to work. First due to old data format, but after using uvt_convert it does not work neither
UV_MFLAG task
Compare the PdBI uv table with an uv table calculated from a model source and flag the data if the REAL part of the visibility differs from the model in more that a given tolerance. Data are flagged setting weights to 0. NOT TESTED


next up previous contents index
Next: Fitting (GO UVFIT and Up: Interacting with tables Previous: Visualization (GO UVALL and   Contents   Index
Gildas manager 2018-12-15