A MIRIAD uv dataset is composed of a collection of items and ` u-v variables'. The variables are parameters that are known at the time of the observation, and include measured data, and the description of the observation set up ( e.g. correlator set up and observing centres).
Table C.1 gives a list of the items that are used to build up a MIRIAD uv dataset.
Table C.1: MIRIAD
items in a uv visibility dataset
The Programmers Guide contains more detailed information on how a visibility dataset is constructed, this Appendix only reports which variables can be found in the item visdata. The text item vartable contains an ordered (for quick indexing) list of all the variables which exist in the visdata item.
A list of all items in a visibility dataset is summarized in Table C.1 below. A list of all the uv variables can be obtained with the MIRIAD program uvlist.
The storage types (2nd column) in the table below are:
A -- ascii (NULL terminated)
R -- real (32 bit IEEE)
D -- double (64 bit IEEE)
C -- complex (2 * 32 bit IEEE)
I -- integer (32 bit twos complement)
J -- short (16 bit twos complement)
They are the same as the data type in the first column of the vartable item in a MIRIAD uv dataset.
Variables with two dimensions have the first dimension varying fastest, the usual FORTRAN notation.
Name Ty Units Comments
airtemp R centigr. Air temperature at observatory
antdiam R meters Antenna diameter
antpos(nants, 3) D nanosec Antenna equatorial coordinates
atten(nants) I dB Attenuator setting (Hat Ck)
axisrms(2,nants) R arcsec RMS tracking error.
axisrms(1,?) is azimuth error,
axisrms(2,?) is the elevation error.
baseline R - The current antenna baseline
Baseline is stored as
. The uv coordinates are
calculated as
.
Note that this is different from the AIPS/FITS convention
(where
).
When writing this variable, software must ensure that
.
baseline is also known as preamble(4)
chi R radians Position angle of the X feed to the source. This is the
or chi(nants) sum of the parallactic angle and the evector variable.
If only one value is present, all antennas are
assumed to have identical values.
coord(2) D nanosec uv baseline coordinates
coord is also known as preamble(1:2)
corbit R - Number of correlator bits (Hat Ck)
corbw(2) R MHz Correlator bandwidth setting (Hat Ck)
Must take the values
1.25, 2.5, 5.0, 10.0, 20.0, 40.0 & 80.0 MHz.
corfin(4) R MHz Correlator LO setting before doppler tracking (Hat Ck)
This is the LO frequency at zero telescope velocity
Must be in the range 80 to 550 MHz.
cormode I - Correlator mode (Hat Ck). Values are:
1 : 1 window /sideband by 256 channels
2 : 2 windows/sideband by 128 channels
3 : 4 windows/sideband by 64 channels, single sideband
4 : 4 windows/sideband by 64 channels, double sideband
coropt I - Correlator option (Hat Ck)
0 means cross-correlation
1 means auto-correlation
Same as the obstype item?
corr(nchan) J or - Correlation data
R corr is really a complex quantity, but the
data stream variable can be stored otherwise
for efficiency.
cortaper R - On-line correlation taper (Hat Ck)
This is the value at the edge of the window
The value is from 0-1.
ddec R radians Offset in declination from dec in epoch coordinates.
The actual observed DEC is calculated as dec + ddec.
dec R or radians Declination of the observing center. See epoch for coordinate
D definition.
dewpoint R centigr. Dew point at weather station (Hat Ck)
dra R radians Offset in right ascension from ra in epoch coords.
The actual observed RA is calculated as
ra + dra/cos(dec).
epoch R years A badly named variable -- this defines the mean equinox and
equator for the equatorial coordinates ra, dec,
dra and ddec. The epoch of the coordinates is
actually the observing time. Values less than 1984.0 are
Besselian with coordinates in the FK4 system. Values greater
than 1984.0 are Julian with coordinates in the FK5 system.
evector R radians Position angle of the X feed, to the local vertical.
or evector(nants) If only one value is present, all antennas are
assumed to be identical.
focus(nants) R volts Focus setting (Hat Ck)
freq D GHz Rest frequency of the primary line
freqif ? GHz ?
inttime R seconds Integration time
ischan(nspect) I - Starting channel of spectral window
ivalued(nants) I ? Delay step (Hat Ck)
Used in an attempt to calibrate amp and phase vs. delay.
jyperk R Jy/K The efficiency Jy/K,
calculated during calibration
latitud D radians Geodetic latitude of the observatory.
lo1 D GHz First local oscillator (Hat Ck)
lo1 is in the range 70 GHz - 115 GHz.
lo2 D GHz Second local oscillator (Hat Ck)
longitu D radians Longitude of the observatory.
lst D radians Local apparent sidereal time.
mount I - The type of antenna mounts.
or mount(nants) If only one value is given, all antennas
are assumed to be the same. Possible values are:
0: Alt-az mount.
1: Equatorial mount.
nants I - The number of antennas
Following variables use a dimension of nants:
antpos(nants, 3)
focus(nants)
phaselo[1-2](nants)
phasem1(nants)
systemp(nants, nspect)
wsystemp(nants, nwide)
temp(nants, ntemp)
tpower(nants, ntpower)
axisrms(2,nants)
The antennas are always numbered starting at 1.
nchan I - The total number of individual frequency channels
The following variables have the dimension of nchan:
corr(nchan)
npol I - The number of simultaneous polarisations
nschan(nspect) I - Number of channels in spectral window
nspect I Number of spectral windows
Following variables use a dimension of nspect:
ischan(nspect)
nschan(nspect)
restfreq(nspect)
sdf(nspect)
sfreq(nspect)
systemp(nants, nspect)
ntemp I - Number of antenna thermisters
Following variables use a dimension of ntemp:
temp(nants, ntemp)
ntpower I - Number of total power measurements
The following variable depends on ntpower:
tpower(nants,ntpower)
ntpower is currently 1, could be more later.
nwide I - Number of wideband channels
Variables which depend on nwide are:
wfreq(nwide)
wwidth(nwide)
wcorr(nwide)
wsystemp(nants,nwide)
obsdec D radians Apparent declination of the observing centre
at time of observation.
observer(*) A - The name of the observer
obsra D radians Apparent right ascension of the observing centre
at time of observation.
on I - Either 0 or 1, for on and off pointing,
for auto-correlation data.
operator(*) A - The name of the current operator
pbfwhm R arcsec Primary Beam at Full Width Half Maximum
For Hat Ck, it is approximately 11040.0/ lo1.
phaselo1(nants) R radians Antenna phase offset (Hat Ck)
phaselo2(nants) R radians Second LO phase offset (Hat Ck)
phasem1(nants) R radians IF cable phase (Hat Ck)
plangle R degrees Planet angle
plmaj R arcsec Planet major axis (note units)
plmin R arcsec Planet minor axis
pltb R Kelvin Planet brightness
pol I - Polarization type of the correlation data. Values
follow the AIPS/FITS convention, viz:
1: Stokes I
2: Stokes Q
3: Stokes U
4: Stokes V
-1: Circular RR
-2: Circular LL
-3: Circular RL
-4: Circular LR
-5: Linear XX
-6: Linear YY
-7: Linear XY
-8: Linear YX
precipmm R mm Mm of precipitable water vapour in the atmosphere
ra R or radians Right ascension of the observing center. See epoch for
D the definition of the coordinate system.
relhumid R % Relative Humidity at observatory
restfreq(nspect) D GHz Rest frequency for each spectral window.
This may be zero for continuum observations.
sdf(nspect) D GHz Change in frequency per channel
sfreq(nspect) D GHz Sky frequency of first channel in window
source(*) A - The name of the source
systemp R Kelvin Antenna system temperatures
or systemp(nants)
or systemp(nants,nspect)
telescop(*) A - The telescope name. Some standard values are:
'ATCA'
'HATCREEK'
'VLA'
'WSRT'temp R centigr. Antenna thermister temperatures (Hat Ck)
(nants, ntemp)
time D days The time (nominally UT1) stored as a Julain date.
For example, noon on Jan 1, 1980 is 2,444,240.0!
time is also known as preamble(3)
tpower R volts Total power measurements (Hat Ck)
(nants, ntpower)
tscale R - Optional correlation scale factor
Used only when corr is stored as J (16 bits).
ut D radians The time since midnight Universal time (nominally UT1).
veldop R km/sec The sum of the radial velocity of the observatory
(in the direction of the source, with respect to the rest
frame) and the nominal systemic radial velocity of the source.
veltype(*) A - Velocity rest frame. Possible values for veltype are:
VELO-LSR: rest frame is the LSR
VELO-HEL: rest frame is the barycentre
VELO-OBS: rest frame is the observatory
FELO-LSR: rest frame is the LSR (deprecated)
FELO-HEL: rest frame is the barycentre (deprecated)
version(*) A - The current hardware/software version
Current options: oldhat, newhat
vsource R km/sec Nominal radial systemic velocity of source.
Positive velocity is away from observer.
wcorr(nwide) C - Wideband correlations. The current ordering is:
wcorr(1:2) are the digital LSB and USB.
wcorr(3:4) are the analog LSB and USB.
wfreq(nwide) R GHz Wideband correlation average frequencies
winddir(4) A - Wind direction
Encoded as `N', `SE', `W', etc.
windmph R mph Wind speed
wsystemp R K System temperature for wide channels.
or wsystemp(nants)
or wsystemp(nants,nwide)
wwidth(nwide) R GHz Wideband correlation bandwidths
xsampler R percent X sampler statistics (ATCA).
(3,nants,nspect)
xtsys(nants,nspect) R Kelvin System temperature of the X feed (ATCA).
xyamp(nants,nspect) R Jy On-line XY amplitude measurements (ATCA).
xyphase R radians On-line XY phase measurements (ATCA).
(nants,nspect)
ysampler R percent Y sampler statistics (ATCA).
(3,nants,nspect)
ytsys(nants,nspect) R Kelvin System temperature of the Y feed (ATCA).