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0.1.96 sdimaging

Requires:

Synopsis
SD task: imaging for total power and spectral data

Description

Task sdimaging creates an image from input single-dish data sets.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.

The coordinate of output image is defined by four axes, i.e., two spatial axes, frequency and polarization axes.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).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.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.

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.



Arguments





Inputs

infiles

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

allowed:

stringArray

Default:

outfile

name of output image

allowed:

string

Default:

overwrite

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

allowed:

bool

Default:

False

field

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

allowed:

any

Default:

variant

spw

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

allowed:

any

Default:

variant

antenna

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

allowed:

any

Default:

variant

scan

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

allowed:

any

Default:

variant

intent

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

allowed:

any

Default:

variant OBSERVE_TARGET#ON_SOURCE

mode

spectral gridding type

allowed:

string

Default:

channel

nchan

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

allowed:

int

Default:

-1

start

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

allowed:

any

Default:

variant 0

width

width of output spectral channels

allowed:

any

Default:

variant 1

veltype

velocity definition

allowed:

string

Default:

radio

outframe

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

allowed:

string

Default:

gridfunction

gridding function for imaging (see description in help)

allowed:

string

Default:

BOX

convsupport

convolution support for gridding

allowed:

int

Default:

-1

truncate

truncation radius for gridding

allowed:

any

Default:

variant -1

gwidth

HWHM for gaussian

allowed:

any

Default:

variant -1

jwidth

c-parameter for jinc function

allowed:

any

Default:

variant -1

imsize

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)

allowed:

any

Default:

variant

cell

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

allowed:

any

Default:

variant

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)

allowed:

any

Default:

variant

ephemsrcname

ephemeris source name, e.g. ’MARS’

allowed:

string

Default:

pointingcolumn

pointing data column to use

allowed:

string

Default:

direction

restfreq

rest frequency to assign to image, e.g., ’114.5GHz’

allowed:

any

Default:

variant

stokes

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

allowed:

string

Default:

minweight

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

allowed:

double

Default:

0.1

clipminmax

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.

allowed:

bool

Default:

False

Returns
void

Example

 
Keyword arguments:  
infiles -- a list of names of input SD Measurementsets  
        example: ’m100.PM01.ms’  
                 [’m100.PM01.ms’,’m100.PM03.ms’]; multiple MSes  
outfile -- name of output image  
        default: ’’  
        example: ’mySDimage.im’  
overwrite -- overwrite the output file if already exists  
        options: (bool) True,False  
        default: False (do NOT overwrite)  
        example: if True, existing file will be overwritten  
field -- select data by field IDs and names  
                If field string is a non-negative integer, it is assumed to  
                be a field index otherwise, it is assumed to be a  
                field name  
        default: ’’ (use all fields)  
        example: field=’3C2*’ (all names starting with 3C2)  
                 field=’0,4,5~7’ (field IDs 0,4,5,6,7)  
                 field=’0,3C273’ (field ID 3 or filed named 3C273)  
                 For multiple MS input, a list of field strings can be used:  
                 field = [’0~2’,’0~4’] (field ids 0-2 for the first MS and 0-4  
                         for the second)  
                 field = ’0~2’ (field ids 0-2 for all input MSes)  
        this selection is in addition to the other selections to data  
spw -- select data by spectral window IDs/channels  
       NOTE: channels de-selected here will contain all zeros if  
       selected by the parameter mode subparameters.  
        default: ’’ (use all IFs and channels)  
        example: spw=’3,5,7’ (IF IDs 3,5,7; all channels)  
                 spw=’<2’ (IF IDs less than 2, i.e., 0,1; all channels)  
                 spw=’30~45GHz’ (IF IDs with the center frequencies in range 30-45GHz; all channels)  
                 spw=’0:5~61’ (IF ID 0; channels 5 to 61; all channels)  
                 spw=’3:10~20;50~60’ (select multiple channel ranges within IF ID 3)  
                 spw=’3:10~20,4:0~30’ (select different channel ranges for IF IDs 3 and 4)  
                 spw=’1~4;6:15~48’ (for channels 15 through 48 for IF IDs 1,2,3,4 and 6)  
                 For multiple MS input, a list of spw strings can be used:  
                 spw=[’0’,’0~3’] (spw ids 0 for the first MS and 0-3 for the second)  
                 spw=’0~3’ (spw ids 0-3 for all input MSes)  
        this selection is in addition to the other selections to data  
antenna -- select data by antenna names or IDs  
           If antenna string is a non-negative integer, it is  
           assumed to be an antenna index, otherwise, it is  
           considered an antenna name.  
        default: ’’ (all baselines, i.e. all antenna in case of auto data)  
        example: antenna=’PM03’  
                 For multiple MS input, a list of antenna strings can be used:  
                 antenna=[’5’,’6’] (antenna id5 for the first MS and 6 for the second)  
                 antenna=’5’ (antenna index 5 for all input MSes)  
        this selection is in addition to the other selections to data  
scan -- select data by scan numbers  
        default: ’’ (use all scans)  
        example: scan=’21~23’ (scan IDs 21,22,23)  
                 For multiple MS input, a list of scan strings can be used:  
                 scan=[’0~100’,’10~200’] (scan ids 0-100 for the first MS  
                 and 10-200 for the second)  
                 scan=’0~100 (scan ids 0-100 for all input MSes)  
        this selection is in addition to the other selections to data  
intent -- select data by observational intent, also referred to as ’scan intent’  
        default: ’OBSERVE_TARGET#ON_SOURCE’ (ALMA ON-source intent)  
        example: intent=’’ (use all scan intents)  
                 intent=’*ON_SOURCE*’ (any valid scan-intent expression accepted by the MSSelection module can be specified)  
                 For multiple MS input, a list of scan-intent expressions can be used:  
                 intent=[’ON_SOURCE’,’CALIBRATE_BANDPASS’] (scan intent ON_SOURCE for the first MS  
                 and CALIBRATE_BANDPASS for the second)  
        this selection is in addition to the other selections to data  
mode -- spectral gridding type  
        options: ’channel’, ’velocity’, ’frequency’  
        default: ’channel’  
    >>> mode expandable parameters  
       nchan -- Total number of channels in the output image.  
           default: -1; Automatically selects enough channels to cover  
                    data selected by ’spw’ consistent with ’start’ and ’width’.  
                    It is often easiest to leave nchan at the default value.  
           example: nchan=100  
       start -- First channel, velocity, or frequency.  
                For mode=’channel’; This selects the channel index number  
                from the MS (0 based) that you want to correspond to the  
                first channel of the output cube. The output cube will be  
                in frequency space with the first channel having the  
                frequency of the MS channel selected by start.  start=0  
                refers to the first channel in the first selected spw, even  
                if that channel is de-selected in the spw parameter.  
                Channels de-selected by the spw parameter will be filled with  
                zeros if included by the start parameter. For example,  
                spw=3~8:3~100 and start=2 will produce a cube that starts on  
                the third channel (recall 0 based) of spw index 3, and the  
                first channel will be blank.  
           default: ’’ (the first input channel of first input spw)  
           example: start=100 (mode=’channel’)  
                    start=’22.3GHz’ (mode=’frequency’)  
                    start=’5.0km/s’ (mode=’velocity’)  
       width -- Output channel width  
               For mode=’channel’, default=1; width>1 indicates channel averaging  
               example: width=4.  
               For mode= ’velocity’ or ’frequency’, default=’’; width of  
               first input channel, or more precisely, the difference  
               in frequencies between the first two selected channels.  
               -- For example if channels 1 and 3 are selected with spw,  
                then the default width will be the difference between their  
                frequencies, and not the width of channel 1.  
               -- Similarly, if the selected data has uneven channel-spacing,  
                 the default width will be picked from the first two selected  
                 channels. In this case, please specify the desired width.  
               When specifying the width, one must give units  
               examples: width=’1.0km/s’, or width=’24.2kHz’.  
               Setting width>0 gives channels of increasing frequency for  
               mode=’frequency’, and increasing velocity for mode=’velocity’.  
       veltype -- Velocity reference frame of output image  
           Options: ’radio’,’optical’,’true’,’relativistic’  
           default: ’radio’  
outframe -- velocity reference frame of output image  
        Options: ’’,’LSRK’,’LSRD’,’BARY’,’GEO’,’TOPO’,’GALACTO’,  
                 ’LGROUP’,’CMB’  
        default: ’’; same as input data or ’LSRK’ for multiple-MS inputs  
        example: frame=’bary’ for Barycentric frame  
gridfunction -- gridding function for imaging  
        options: ’BOX’ (Box-car), ’SF’ (Spheroidal),  
                 ’PB’ (Primary-beam), ’GAUSS’ (Gaussian),  
                 ’GJINC’ (Gaussian*Jinc)  
        default: ’BOX’  
        example: ’SF’  
    >>> gridfunction expandable parameter:  
       convsupport -- convolution support for ’SF’  
           default: -1 (use default for each gridfunction)  
           example: 3  
       truncate -- truncattion radius of convolution kernel.  
                   effective only for ’GAUSS’ and ’GJINC’.  
           default: ’-1’ (use default for each gridfunction)  
           example: 3, ’20arcsec’, ’3pixel’  
       gwidth -- HWHM for gaussian. Effective only for  
                 ’GAUSS’ and ’GJINC’.  
           default: ’-1’ (use default for each gridfunction)  
           example: 3, ’20arcsec’, ’3pixel’  
       jwidth -- Width of jinc function. Effective only for  
                 ’GJINC’.  
           default: ’-1’ (use default for each gridfunction)  
           example: 3, ’20arcsec’, ’3pixel’  
imsize -- x and y image size in pixels, symmetric for single value  
        default: [] (=cover all pointings in MS)  
        example: imsize=200 (equivalent to [200,200])  
cell -- x and y cell size. default unit arcmin  
        default: ’’ (= 1/3 of FWHM of primary beam)  
        example: cell=[’0.2arcmin, 0.2arcmin’]  
                 cell=’0.2arcmin’ (equivalent to example above)  
phasecenter -- image phase center: direction measure or field ID  
        default: ’’ (= the center of pointing directions in  
                     POINTING table of infiles)  
        example: 6 (field id), ’J2000 13h44m00 -17d02m00’,  
                 ’AZEL -123d48m29 15d41m41’  
ephemsrcname -- ephemeris source name for moving source (solar sytem objects)  
        default: ’’ (none)  
        if the source name in the data matches one of the solar system  
        objects known by CASA, the imaging realigns the data by  
        correcting shifts of the source during observation,  
        so that the source appears to be fixed in the image.  
        examples: ’MERCURY’, ’VENUS’, ’MARS’, ’JUPITER’, ’SATURN’,  
                  ’URANUS’, ’NEPUTUNE’, ’PLUTO’, ’SUN’, ’MOON’  
pointingcolumn -- pointing data column to use  
        option: ’direction’, ’target’, ’pointing_offset’, ’source_offset’, encoder’  
        default: ’direction’  
restfreq -- specify rest frequency to use for output image  
        default: ’’ (refer input data)  
        example: 1.0e11, ’100GHz’  
stokes -- stokes parameters or polarization types to image  
        default: ’’ (use all polarizations)  
        example: ’XX’  
minweight -- Minimum weight ratio to the median of weight used in  
             weight correction and weight based masking  
        default: 0.1  
        example: minweight = 0.  
clipminmax -- 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.  
        default: False  
        option: True, False  
 
 
-----------------  
Gridding Kernel  
-----------------  
The parameter gridfunction sets gridding function (convolution kernel)  
for imaging. Currently, the task supports ’BOX’ (Box-car), ’SF’ (Prolate  
Spheroidal Wave Function), ’GAUSS’ (Gaussian), ’GJINC’ (Gaussian*Jinc),  
where Jinc(x) = J_1(pi*x/c)/(pi*x/c) with a first order Bessel function  
J_1, and ’PB’ (Primary Beam). For ’PB’, correct antenna informations  
should be included in input file.  
 
There are four subparameters for gridfunction: convsupport, truncate,  
gwidth, and jwidth. The convsupport is an integer specifying cut-off  
radius for ’SF’ in units of pixel. By default (convsupport=-1),  
the cut-off radius is set to 3 pixels. The truncate is a cut-off  
radius for ’GAUSS’ or ’GJINC’. It accepts integer, float, and  
string values of numeric plus unit. Allowed units are angular  
units such as ’deg’, ’arcmin’, ’arcsec’, and ’pixel’. Default unit  
is ’pixel’ so that string without unit or numerical values (integer  
or float) will be interpreted as radius in pixel. Default value  
for truncate, which is used when negative radius is set, is 3*HWHM  
for ’GAUSS’ and radius at first null for ’GJINC’. The gwidth is  
the HWHM of gaussian for ’GAUSS’ and ’GJINC’. Default value is  
sqrt(log(2)) pixel for ’GAUSS’ and 2.52*sqrt(log(2)) pixel for  
’GJINC’. The jwidth specifies width of the jinc function (parameter  
’c’ in the definition above). Default is 1.55 pixel. Both gwidth  
jwidth allows integer, float, or string of numeric plus unit.  
Default values for gwidth and jwidth are taken from Mangum et al.  
(2007). Formula for ’GAUSS’ and ’GJINC’ are taken from Table 1 in  
the paper, and are written as below using gwidth and jwidth:  
 
   GAUSS: exp[-log(2)*(|r|/gwidth)**2]  
 
   GJINC: J_1(pi*|r|/jwidth)/(pi*|r|/jwidth)  
             * exp[-log(2)*(|r|/gwidth)^2]  
 
 
Reference: Mangum, et al. 2007, A&A, 474, 679-687  
 
--------------------  
Mask in Output Image  
--------------------  
The parameter minweight defines a threshold of weight values  
to mask. The pixels in outfile whose weight is smaller than  
minweight*median(weight) are masked out. The task also creates  
a weight image with the name outfile.weight.  
 


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