sdimaging – SD task: imaging for total power and spectral data – single dish task

Description

Task sdimaging creates an image from input single-dish data sets.n The input can be either total power and spectral data. Currently, this task directly accesses the Measurement Set data because of the data access efficiency. So it differs from other single-dish tasks that mostly operate on the ASAP scantable data format.n

The coordinate of output image is defined by four axes, i.e., two spatial axes, frequency and polarization axes.n By default, spatial coordinate of image is defined so that the all pointing directions in POINTING tables of input data sets are covered with the cell size, 1/3 of FWHM of primary beam of antennas in the first MS. Therefore, it is often easiest to leave spatial definitions at the default values. It is also possible to define spatial axes of the image by specifying the image center direction (phasecenter), number of image pixel (imsize) and size of the pixel (cell).n The frequency coordinate of image is defined by three parameters, the number of channels (nchan), the channel id/frequency/velocity of the first channel (start), and channel width (width).There are three modes available to define unit of start and width, i.e., ‘channel’ (use channel indices), ‘frequency’ (use frequency unit, e.g., ‘GHz’), and ‘velocity’ (use velocity unit, e.g., ‘km/s’). By default, nchan, start, and width are defined so that all selected spectral windows are covered with the channel width equal to separation of first two channels selected.n Finally, polarizations of image is defined by stokes parameter or polarization.For example, stokes=’XXYY’ produces an image cube with each plane contains the image of one of the polarizations, while stokes=’I’ produces a ‘total intensity’ or Stokes I image.n

The task also supports various grid function (convolution kernel) to weight spectra as well as an option to remove the most extreme minimum and maximum (unweighted) values prior to computing the gridded pixel values. See description below for details of gridfunction available.

Parameters

Title

Parameter	Default	Description
infiles	numpy.array( [  ] )
outfile	''
overwrite	False	overwrite the output file if already exists [True, False]
field	''
spw	''
antenna	''
scan	''
intent	'OBSERVE_TARGET#ON_SOURCE'
mode	'channel'	spectral gridding type [“channel”, “frequency”, “velocity”]
nchan	int(-1)
start	int(0)
width	int(1)
veltype	'radio'	velocity definition [“radio”, “optical”, “true” or “relativistic”]
outframe	''	velocity frame of output image [“lsrk”, “lsrd”, “bary”, “geo”, “topo”, “galacto”, “lgroup”, “cmb”] (“”=current frame or LSRK for multiple-MS inputs)
gridfunction	'BOX'	gridding function for imaging [“BOX”, “SF”, “PB”, “GAUSS” or “GJINC”] (see description in help)
convsupport	int(-1)
truncate	int(-1)
gwidth	int(-1)
jwidth	int(-1)
imsize	*UNKNOWN*
cell	''
phasecenter	''
projection	'SIN'
ephemsrcname	''
pointingcolumn	'direction'	pointing data column to use [“direction”, “target”, “pointing_offset”, “source_offset” or “encoder”]
restfreq	''
stokes	''
minweight	float(0.1)	Minimum weight ratio to use
brightnessunit	''
clipminmax	False	Clip minimum and maximum value from each pixel

Parameter Explanations

infiles

numpy.array( [  ] )

a list of names of input SD Measurementsets (only MS is allowed for this task)

outfile

''

name of output image

overwrite

False

overwrite the output file if already exists [True, False]

field

''

select data by field IDs and names, e.g. “3C2*” (“”=all)

spw

''

select data by IF IDs (spectral windows), e.g. “3,5,7” (“”=all)

antenna

''

select data by antenna names or IDs, e.g, “PM03” (”” = all antennas)

scan

''

select data by scan numbers, e.g. “21~23” (“”=all)

intent

'OBSERVE_TARGET#ON_SOURCE'

select data by observational intent, e.g. “ON_SOURCE” (“”=all)

mode

'channel'

spectral gridding type

nchan

int(-1)

number of channels (planes) in output image (-1=all)

start

int(0)

start of output spectral dimension, e.g. “0”, “110GHz”, “-20km/s”

width

int(1)

width of output spectral channels

veltype

'radio'

velocity definition

outframe

''

velocity frame of output image (“”=current frame or LSRK for multiple-MS inputs)

gridfunction

'BOX'

gridding function for imaging (see description in help)

convsupport

int(-1)

convolution support for gridding

truncate

int(-1)

truncation radius for gridding

gwidth

int(-1)

HWHM for gaussian

jwidth

int(-1)

c-parameter for jinc function

imsize

*UNKNOWN*

x and y image size in pixels, e.g., [64,64]. Single value: same for both spatial axes ([] = number of pixels to cover whole pointings in MSes)

cell

''

x and y cell size, (e.g., [“8arcsec”,”8arcsec”]. default unit arcmin. (”” = 1/3 of FWHM of primary beam)

phasecenter

''

image center direction: position or field index, e.g., “J2000 17:30:15.0 -25.30.00.0”. (”” = the center of pointing directions in MSes)

projection

'SIN'

map projection type

ephemsrcname

''

ephemeris source name, e.g. “MARS”

pointingcolumn

'direction'

pointing data column to use

restfreq

''

rest frequency to assign to image, e.g., “114.5GHz”

stokes

''

stokes parameters or polarization types to image, e.g. “I”, “XX”

minweight

float(0.1)

Minimum weight ratio to the median of weight used in weight correction and weight beased masking

brightnessunit

''

Overwrite the brightness unit in image ('' = respect the unit in MS) ['K' or 'Jy/beam']

clipminmax

False

Clip minimum and maximum value from each pixel. Note the benefit of clipping is lost when the number of integrations contributing to each gridded pixel is small, or where the incidence of spurious datapoints is approximately or greater than the number of beams (in area) encompassed by expected image.