ALMA Antenna responses in CASA imaging - NRAO Safe Server · D. Petry, CALIM 2012, Capetown,...
Transcript of ALMA Antenna responses in CASA imaging - NRAO Safe Server · D. Petry, CALIM 2012, Capetown,...
1D. Petry, CALIM 2012, Capetown, December 2012
ALMA Antenna responses in CASA imagingDirk Petry (ESO), December 2012
Outline
→ Motivation → ALBiUS/ESO work on CASA responses infrastructure and ALMA beam library
→ First test results
2D. Petry, CALIM 2012, Capetown, December 2012
Motivation
ALMA performance (τ=60s, 50 antennas)ALMA data can only be taken in one band at a time.
Bands 3, 6, 7, and 9 have been available for Early Science since 2011.Bands 4, 5, 8, and 10 have seen first light. Bands 1, 2 and 11 in preparation.
10 787-950 0.3-0.4 0.36 ... 0.0045 118 2.0 7 5
ALMA covers a wide frequency range with 10, possibly 11 different receivers.
3D. Petry, CALIM 2012, Capetown, December 2012
Motivation
FOV often too small to cover extended objects - i.e. imaging will often be mosaicing, sometimes “wide-field imaging' - direction-dependent effects need to be taken into account more accurately - requires good knowledge of the instrument's primary beam (dropping assumptions like rotational symmetry)
The price for the improved performancemm/sub-mm calibration and imaging problems (continued)
4) FOV often too small to cover extended objects - i.e. imaging will often be “wide-field imaging”, mosaicing - direction-dependent effects need to be taken into account more accurately - requires good knowledge of the instrument's primary beam (dropping assumptions like rotational symmetry) - need to take into account the w-term, i.e. the sky curvature when image radius exceeds r
max[arcmin] = sqrt( λ[cm] . phase error [deg] / b
max[km])
Band \ b
max 0.2 km 7 km 16 km
2 rmax
=
4 6 8 10
To achieve high continuum sensitivity, need to integrate over wide band - frequency-dependence of the primary beam becomes important (although less so than for EVLA since fractional bandwidth smaller) - the source spectrum may need to be unfolded in parallel (often have thermal and non-thermal sources in the same image)
- 4 different antenna types: Main Array: DA (= AEM), DV (= Vertex), PM (=Melco) all 12 m but different struts ACA: 7m antennas Full use of ALMA or ALMA + ACA requires handling of heterogeneous baselines
⇒ ALBiUS funded work on ALMA primary beams at ESO 2009 - 2011 (work continues, funded by ESO)
4D. Petry, CALIM 2012, Capetown, December 2012
ALMA/CASA imaging work at ESOa) Assessment of Status Quo
Up to CASA 3.2 (mid 2011), all primary beams in CASA are analytical
For ALMA it is an Airy disk.
Band 3 observation of a 11 point mosaic on a bright quasar * * * * with 12 ALMA antennas in May 2011 analysed with CASA 3.2 * * *immediately demonstrated the strong need for improvements. * * * * mosaic pattern (gives 3 offsets)
0 25 43 arcsecs offset
relativereconstr.flux 1.6
1.4
1.2
1.0
Adjusting the ALMA Airy disk
Green: 12.0 m Airy disk (v3.2)
Red: 10.7 m
Yellow: 10.4 m
Blue: 10.2 m
5D. Petry, CALIM 2012, Capetown, December 2012
ALMA/CASA imaging work at ESOa) Assessment of Status Quo
Up to CASA 3.2 (mid 2011), all primary beams in CASA are analytical
For ALMA it is an Airy disk.
Band 3 observation of a 11 point mosaic on a bright quasar * * * * with 12 ALMA antennas in May 2011 analysed with CASA 3.2 * * *immediately demonstrated the strong need for improvements. * * * * mosaic pattern (gives 3 offsets)
0 25 43 arcsecs offset
relativereconstr.flux 1.6
1.4
1.2
1.0
Adjusting the ALMA Airy disk
Green: 12.0 m Airy disk (v3.2)
Red: 10.7 m adopted in v3.4 (in prerelease Dec. 11)Yellow: 10.4 m
Blue: 10.2 m
Still inaccurate by 10%at larger offsets
6D. Petry, CALIM 2012, Capetown, December 2012
CASA status since v3.4
Primary beam library available for actual imaging:EVLA, ALMA, ATA, ATCA, BIMA, HATCREEK, CARMA, GBT, GMRT, IRAMPDB, SMA, WSRT
ALMA, EVLA, ATCA, GBT, and WSRT (and SMA?) are polynomials or Airy disks fitted to measurements of the beam of the actual telescope.Only VLA includes beam squint.
In particular ALMA uses an Airy disk for an effective dish diameter of 10.7 m (i.e. scaled down from 12 m by factor 1.12)
E.g., the Fomalhaut ApJ Letter (Boley et al., 2012) usedthis PB down to 7% power.
7D. Petry, CALIM 2012, Capetown, December 2012
ALMA/CASA Imaging work at ESOb) enable use of response images
1) Creation of the AntennaResponses C++ class in casacore - a database for antenna responses in different representations - define which primary beam is in use for which observatory which antenna type which time range which elevation range which beam (if there is more than one)
2) Extension of the BeamCalc ray tracing code (W. Brisken) for general use + adding astigmatism feature
3) Upgrade of the Voltage Pattern Manager (“vpmanager”) to connect to AntennaResponses databases - user interface at the Python level of CASA 4) (ongoing) Tests and optimisations of the above
8D. Petry, CALIM 2012, Capetown, December 2012
Best source of ALMA responses so far: The TICRA simulations of ALMA electrical field patterns (2007)Simulated were three antenna designs
1) Vertex (built by VertexRSI): space framework struts2) AEM (built by Thales Alenia, European Industrial Engineering, and MT Aerospace): elliptical struts with cladding
3) ideal antenna: no struts
MELCO 12m and 7m AEM Vertex
ALMA/CASA Imaging work at ESOb) enable use of response images
9D. Petry, CALIM 2012, Capetown, December 2012
Best source of ALMA responses so far: The TICRA simulations of ALMA electrical field patterns (2007)Simulated were three antenna designs
1) Vertex (built by VertexRSI): space framework struts (also good approx. of Melco)2) AEM (built by Thales Alenia, European Industrial Engineering, and MT Aerospace): elliptical struts with cladding
3) ideal antenna: no struts (not used here)
MELCO 12m and 7m AEM Vertex
ALMA/CASA Imaging work at ESOb) enable use of response images
10D. Petry, CALIM 2012, Capetown, December 2012
The TICRA simulations of ALMA electrical field patterns Detailed front end geometry with secondary mirror taken into account where available: Bands 1, 5, 8: design still preliminary in 2007, only Gaussian beam simulated Bands 3, 4, 6, 7, 9: complete simulation at 3 or 4 frequencies within band Bands 2, 10: design incomplete in 2007, not simulated ⇒ Electric Field Patterns (co- and cross-polar for both X and Y) in GRASP format
Examples of front end geometries: Band 3 (left), Band 7 (right)
ALMA/CASA Imaging work at ESOb) enable use of response images
11D. Petry, CALIM 2012, Capetown, December 2012
The TICRA simulations of ALMA electrical field patterns
Simulated Electric Field Patterns (copolar field, X) for bands 1 and 3 to 9 (Vertex Struts)
Normalised magnitudeof E-field
Simulated Electric Field Patterns (crosspolar field, X) for bands 3, 4, 6, 7, 9 (Vertex Struts)
Band 1 (31 GHz) Band 3 (100 GHz) Band 4 (144 GHz) Band 5 (187 GHz) Band 6 (243 GHz) Band 7 (324 GHz) Band 8 (500 GHz) Band 9 (720 GHz)
Band 3 (100 GHz) Band 4 (144 GHz) Band 6 (243 GHz) Band 7 (324 GHz) Band 9 (720 GHz)
1.4”30”
ALMA/CASA Imaging work at ESOb) enable use of response images
12D. Petry, CALIM 2012, Capetown, December 2012
ALMA/CASA Imaging work at ESOb) enable use of response images
The TICRA GRASP format response images converted to Voltage Pattens inCASA Image format.
CASA response image format agreed with NRAO imaging team:
- Four-plane (in the Stokes dimension) complex-valued image
containing the voltage pattern for the parallel hands (XX and YY)
and the cross-hands (XY and YX).
- Directional coordinate system of type AZELGEO centered on (0.,0.).
- Reference frequency of the responses stored by creating a
degenerate spectral axis centered on that frequency.
CASA 3.4 and 4.0: vpmanager part of CASA but not yet connected to CASA imaging. Cannot use the new ALMA PB library in normal imaging.But a patch was made to permit at least post-deconvolution correctionwith a single PB (homogeneous array case).With this patch, more tests were carried out.
13D. Petry, CALIM 2012, Capetown, December 2012
ALMA/CASA Imaging work at ESO Tests on ALMA data
Second test dataset: January 2012, 4 SPWs in Band 3, 19 antennas (14 DV, 3 PM, 2 DA) 61 point mosaic on Quasar samples 9 different offsets
Image each pointing individually, re-center resulting images to the nominal Quasar position, then superimpose using individual masks ⇒ easily understandable plots like this:
* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
14D. Petry, CALIM 2012, Capetown, December 2012
ALMA Early Science, 99.9 GHz,hour angle = -1 h,analysed with CASA 3.3 defaultALMA PB correction
ALMA/CASA Imaging work at ESO Tests on ALMA data
15D. Petry, CALIM 2012, Capetown, December 2012
ALMA Early Science, 99.9 GHz,hour angle = -1 h,analysed with CASA 3.3 defaultALMA PB correction
0 10 20 30 40 50 60 arcs
rel.flux100
10
1
0.1
ALMA/CASA Imaging work at ESO Tests on ALMA data
16D. Petry, CALIM 2012, Capetown, December 2012
ALMA Early Science, 99.9 GHz,hour angle = -1 h,analysed with CASA 3.3 without any PB correction
0 10 20 30 40 50 arcs
rel.flux10
1
0.1
0.01
0.5
0.05
ALMA/CASA Imaging work at ESO Tests on ALMA data
17D. Petry, CALIM 2012, Capetown, December 2012
ALMA Early Science, 99.9 GHz,hour angle = -1 h,analysed with CASA 3.4 defaultPB corr. (scaled Airy disk)
0 10 20 30 40 50 arcs
rel.flux100
10
1
0.1
ALMA/CASA Imaging work at ESO Tests on ALMA data
18D. Petry, CALIM 2012, Capetown, December 2012
ALMA Early Science, 99.9 GHz,hour angle = -1 h,analysed with CASA 3.4using TICRA sim. PB image
0 10 20 30 40 50 arcs
rel.flux100
10
1
0.1
No systematic deviations out to at least 2 PB radii.
ALMA/CASA Imaging work at ESO Tests on ALMA data
19D. Petry, CALIM 2012, Capetown, December 2012
ALMA Early Science, 99.9 GHz,hour angle = -1 h,analysed with CASA 3.4using TICRA sim. PB image
0 10 20 30 40 50 arcs
rel.flux
1.2
1.0
0.8
Remaining scatter mostly due to noise.
1.1
0.9
0.7
ALMA/CASA Imaging work at ESO Tests on ALMA data
20D. Petry, CALIM 2012, Capetown, December 2012
Tests ongoing.
- See consistent results at other freqs. in Band 3.
- Frequency scaling seems to work (have between 2 and 3 responses per band, use scaling to interpolate)
- Analysis of Band 6 data under way. More data forthcoming
- For tests of parallactic angle issues (field rotation) need brighter source at larger offsets
- Crosshands still need to be investigated when ALMA data with full polarisation become available.
- Following slides: Some examples of the simulated responses
ALMA/CASA Imaging work at ESO Tests on ALMA data - status
21D. Petry, CALIM 2012, Capetown, December 2012
ALMA/CASA Imaging work at ESOSimulated Voltage Pattern Examples
Vertex XX Voltage Pattern (Band 3, 100 GHz)
22D. Petry, CALIM 2012, Capetown, December 2012
AEM XX Voltage Pattern (Band 3, 100 GHz)
ALMA/CASA Imaging work at ESOSimulated Voltage Pattern Examples
23D. Petry, CALIM 2012, Capetown, December 2012
AEM XX Voltage Pattern (Band 7, 324 GHz)
ALMA/CASA Imaging work at ESOSimulated Voltage Pattern Examples
24D. Petry, CALIM 2012, Capetown, December 2012
AEM XX Voltage Pattern (Band 9, 661 GHz)
ALMA/CASA Imaging work at ESOSimulated Voltage Pattern Examples
25D. Petry, CALIM 2012, Capetown, December 2012
ALMA/CASA Imaging work at ESO additional ray-tracing simulations
Finally: working on alternative ray-tracing simulation (based on code by W. Brisken) of beams not available from TICRA (via aperture illumination pattern) (e.g. 7m beams, Bands 2, 10, and 11, and astigmatic reflectors in all bands)Up to first null, results look promissing; good agreement with TICRA simulationPrototype is available in CASA 4.0.
TICRA sim. ray-tracedVertex XX100 GHz
Vertex XX100 GHz
26D. Petry, CALIM 2012, Capetown, December 2012
ALMA/CASA Imaging work at ESO additional ray-tracing simulations
Finally: working on alternative ray-tracing simulation (based on code by W. Brisken) of beams not available from TICRA (via aperture illumination pattern) (e.g. 7m beams, Bands 2, 10, and 11, and astigmatic reflectors in all bands)
Examples of simulated ALMA 12 m beams with astigmatism:
Z5 = 0.05 Z6 = 0.05Vertex XX100 GHz
Vertex XX100 GHz