What's the difference between Antenna1 and Antenna2? Axis definitions in plotms

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Plotms is a powerful tool for visualizing your measurement set, and provides you with lots of choices for X- and Y- Axes. It's not always clear what the choices mean, so below are some explanations.

Scan

The scan number, as listed by listobs.

Field

The field number, as listed by listobs. Typically, each source should have a different field number.

Time

The time at which the visibility was observed, given in terms of calendar year (yyyy/mm/dd/hh:mm:ss.ss)

Time_interval

The integration time in seconds.

Spw

The spectral window number (analogous to what VLA users know as an IF). The characteristics of each spectral window are listed in listobs.

Channel

The frequency channel number.

Frequency

Frequency in units of GHz. The frame for the frequency (e.g., topocentric, barycentric, LSRK) can be set in the Trans tab of plotms.

Corr

Correlations which have been assigned integer IDs:

5: RR
6: RL
7: LR
8: LL

Antenna1, Antenna2

Antenna1 is the first antenna in a baseline pair; for example, for baseline 2-4, Antenna1 = 2. Antenna2 is the second antenna in a baseline pair; so for baseline 2-4, Antenna2 = 4. Antennae are numbered according to the antenna IDs listed in listobs.

Antenna

For plotting antenna-based quantities like elevation, use just plain Antenna. Antennae are numbered according to the antenna IDs listed in listobs.

Baseline

The baseline number.

UVDist, UVDist_L

Projected baseline separations. UVDist is in units of meters, while UVDist_L is in units of the observing wavelength (lambda, not kilolambda). Note that UVDist_L is a function of frequency, while UVDist is not. Therefore, when plotting UVDist_L, there will be a different data point for each frequency channel.

U, V, W

u, v, and w in units of meters

???

Is this true about the units? Clearly it is in the same units as UVDist

???

Velocity

Velocity, which can be defined by parameters in the Trans tab of plotms, in units of km/s.

Amp

Data amplitudes in units of Jansky.

Phase

Data phases in units of degrees.

Real, Imag

The real and imaginary parts of the visibility in units of Jansky.

Flag

Data which are flagged have Flag = 1, whereas unflagged data are set to Flag = 0. Note that, to display flagged data, you will have to click on the Display tab and choose a 'Flagged Points Symbol'.

Azimuth, Ant-Azimuth

Antenna azimuth in units of degrees. Azimuth is the baseline-based version, while Ant-Azimuth is the antenna-based version.

Elevation, Ant-Elevation

Antenna elevation in units of degrees. Elevation is the baseline-based version, while Ant-Elevation is the antenna-based version.

HourAngle

Hour Angle in units of hours. This is a baseline-based quantity.

ParAngle, Ant-ParAng

Parallactic angle in units of degrees (???)

???

It appears that Ant-ParAng is in reasonable units to be in degrees, whereas ParAng gives totally different numbers, which are too small to be in degrees.

???

Row

Data row number.

???

For each time integration, is there a new row created?

???

FlagRow

???

I would think this is the row number in the flag table for flagged data, but it appears that all data, even that which is flagged, has FlagRow = 0

???

Last checked in CASA Version 3.0.1 (r10380).

--Laura Chomiuk 04:42, 19 February 2010 (UTC)