uv_distance_max, uv_distance_min; (From John Tobin)

[Bonnarel]

From John Tobin
uv_distance_max, uv_distance_min; This might not quite be fine-grained enough because you might have one really long baseline and one very short baseline, but an array is actually configured somewhere in between. Perhaps also adding a 75th percentile baseline and 50th percentile baseline distance would be useful to add to this since those values would provide more information about where most of the uv-coverage is concentrated.

[Bonnarel]

From John Tobin uv_distance_max, uv_distance_min; This might not quite be fine-grained enough because you might have one really long baseline and one very short baseline, but an array is actually configured somewhere in between. Perhaps also adding a 75th percentile baseline and 50th percentile baseline distance would be useful to add to this since those values would provide more information about where most of the uv-coverage is concentrated.

From François Bonnarel :

Good point, we were already wondering how to estimate "effective numbers" for these two quantities in order to avoid "outliers". Your percentile is an interesting proposal to investigate. Or can we find another significant minimum and maximum estimation ?

[Bonnarel]

From John Tobin uv_distance_max, uv_distance_min; This might not quite be fine-grained enough because you might have one really long baseline and one very short baseline, but an array is actually configured somewhere in between. Perhaps also adding a 75th percentile baseline and 50th percentile baseline distance would be useful to add to this since those values would provide more information about where most of the uv-coverage is concentrated.

From François Bonnarel :

Good point, we were already wondering how to estimate "effective numbers" for these two quantities in order to avoid "outliers". Your percentile is an interesting proposal to investigate. Or can we find another significant minimum and maximum estimation ?

From Baptiste Cecconi :

Well, for dense-core arrays, there might be very few "outlier" baselines, but those are a very significant addition to the core. Hence, we (NenuFAR team) would like to keep the min and max values as they are. Remember that this metadata should be filled for each observations, hence those values should contain the actual baseline min and max values for an observation, not a generic value for the instrument. Since we are building data discovery metadata, the uv coverage keywords should be consistent with each shared dataset.

[Bonnarel]

From John Tobin uv_distance_max, uv_distance_min; This might not quite be fine-grained enough because you might have one really long baseline and one very short baseline, but an array is actually configured somewhere in between. Perhaps also adding a 75th percentile baseline and 50th percentile baseline distance would be useful to add to this since those values would provide more information about where most of the uv-coverage is concentrated.

From François Bonnarel :
Good point, we were already wondering how to estimate "effective numbers" for these two quantities in order to avoid "outliers". Your percentile is an interesting proposal to investigate. Or can we find another significant minimum and maximum estimation ?

From Baptiste Cecconi :

Well, for dense-core arrays, there might be very few "outlier" baselines, but those are a very significant addition to the core. Hence, we (NenuFAR team) would like to keep the min and max values as they are. Remember that this metadata should be filled for each observations, hence those values should contain the actual baseline min and max values for an observation, not a generic value for the instrument. Since we are building data discovery metadata, the uv coverage keywords should be consistent with each shared dataset.

From John Tobin :

The 75 percentile uv distance is not a generic value, but could be calculated for each dataset. I get your point that dense core arrays will have fewer outlier baselines, but the density of uv points will be such that the beam one gets from imaging a dataset would be more reliably characterized by something like the 75th percentile baseline rather than the max uv distance. I think there would be value in min, max, and something in between like 75th percentile.

[kettenis]

This is likely to be an issue for VLBI in particular where such outlier baselines are somewhat common. That said, I think users probably will use these parameters to pre-select candidate observations but will always need to look closely at the actual UV-coverage and/or UV-distance plots to determine whether the selected observations actually do meet the scientific requirements.