algorithm development · algorithm development saspo meeting, charlottesville, nov. 9th 2010 s....
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Algorithm Development
SASPO Meeting, Charlottesville, Nov. 9th 2010
S. BhatnagarNRAO
2/21S. Bhatnagar: SASPO Meeting, CV, Nov. 9th 2010
Overview
• Issues requiring new algorithms– Wide-band imaging + off-axis effects
– Wide-band polarization calibration
– HPC, Pipeline processing, Automatic RFI removal(EVLA Memo #139 & #122)
• Progress so far• Various algorithmic dependencies
• Staged deployment recognizing the available resources
– Connection between algorithms R&D and HPC
– Issues and challenges: Research, required software development, etc.
3/21S. Bhatnagar: SASPO Meeting, CV, Nov. 9th 2010
Algorithms R&D Plan
• Guiding principles for algorithms R&D plan 1. Enable new scientific capabilities as soon as possible
(with the given resources)
2. Recognize algorithmic dependencies
3. Develop an integrated plan for staged algorithm R&D, HPC
4. Develop algorithms that can utilize HPC
● Work closely with the HPC development group and plan
4/21S. Bhatnagar: SASPO Meeting, CV, Nov. 9th 2010
Imaging issues
• Requirements– Full-beam, wide-band, full-Stokes imaging
– Mosaicking (including heterogeneous arrays)
• Algorithms R&D required:– Wide-band issues (2:1 Bandwidth ratio)
– Account for frequency dependence of the sky-emission (MFS)
– Polarization dependence of the sky-emission (RM-Synthesis)
– Wide-field issues– Time varying Primary Beam effects
– Frequency and polarization dependence of the PB
– Full-field, wide-band issues– Integration of the various new algorithms
– Mosaicking
5/21S. Bhatnagar: SASPO Meeting, CV, Nov. 9th 2010
Calibration issues
• On-axis (Direction independent)– Wide-band bandpass calibration
– Time varying component
– Frequency dependent polarization – Time varying component
• Off-axis (Direction dependent)– Frequency dependence of the PB
– Time dependence due PB rotation/shape
– Ionosphere (L/S band), atmosphere (ALMA)
– Beam polarization
• RFI– Auto-/semi-automatic flagging algorithms
– High dynamic range imaging: Removal of weak RFI
6/21S. Bhatnagar: SASPO Meeting, CV, Nov. 9th 2010
Time varying DD gains due to PB
1.0 GHz
1.5 GHz
2.0 GHz
+
Continuum wide-bandPower pattern
7/21S. Bhatnagar: SASPO Meeting, CV, Nov. 9th 2010
Wide-band implies Wide-field imaging
● EVLA @L-Band● BW=600 MHz (1.2 – 1.8 GHz)
● Algorithmic Challenge: - Time-varying direction-dependent gains
- Wide-band effects
- Extended emission with superimposed compact emission
- Full Stokes + Mosaicking
8/21S. Bhatnagar: SASPO Meeting, CV, Nov. 9th 2010
Wide-band Imaging
● 3C286, BW=1.0-2.1 GHz● No wide-band modeling of the sky emission
● DR: 1600
● 3C286, BW=1.0-2.1 GHz● With MS-MFS (freq. Dependent model for the sky emission)
● DR: >110,000
9/21S. Bhatnagar: SASPO Meeting, CV, Nov. 9th 2010
Wide-band Imaging
● EVLA @ C-Band● Total BW: 2x2GHz
Stokes-I Image Spectral Index Image
10/21S. Bhatnagar: SASPO Meeting, CV, Nov. 9th 2010
Status: Imaging
• Wide-field imaging– W-Projection: In use (IEEE, 2010)
– PB Corrections» Basic algorithm: AW-Projection (Testing/A&A,2008)» Frequency dependence: Work in progress» Extending to Heterogeneous arrays (ALMA): In progress
» Inclusion of arbitrary antenna PBs: Some work required » Integration with mosaicking: Work required» Polarization dependence: Work needed
– Pointing SelfCal» R&D stage: In progress
11/21S. Bhatnagar: SASPO Meeting, CV, Nov. 9th 2010
Status: Imaging
• Wide-band imaging– MS-MFS (Rau, PhD Thesis (2010))
» No correction for the PB effects
– Scientific testing in progress
– Integration with PB-correction» Re-factoring of the code: Work in progress
● Integration of MS-MFS and A-Projection● Numerical testing● Extension to full-Stokes: R&D required
• Full-Stokes, wide-band imaging– R&D required
• Automatic RFI removal - programming work needed• Pipeline processing – work needed
12/21S. Bhatnagar: SASPO Meeting, CV, Nov. 9th 2010
● 3C147 field at L-Band
● Only 12 antennas used● Bandwidth: 128 MHz● ~7 hr. integration
● Dynamic range: ~700,000:1
● A single baseline based correction was applied
EVLA L-Band Stokes-I: Before correction
13/21S. Bhatnagar: SASPO Meeting, CV, Nov. 9th 2010
● 3C147 field at L-Band
● Only 12 antennas used● Bandwidth: 128 MHz● ~7 hr. integration
● Dynamic range: ~700,000:1
EVLA L-Band Stokes-I: After correction
14/21S. Bhatnagar: SASPO Meeting, CV, Nov. 9th 2010
EVLA L-Band Stokes-V: Before correction
Is it M s , Poln ?Or is it I s , Poln?
V ijObs
= Mij∫M ijS s I s e2 bij . sd s
15/21S. Bhatnagar: SASPO Meeting, CV, Nov. 9th 2010
EVLA L-Band Stokes-I: After correction
Use physical model for the Stokes-V pattern:
Contours: Stokes-I power patternColour: Stokes-V power pattern
16/21S. Bhatnagar: SASPO Meeting, CV, Nov. 9th 2010
3C147: Residual errors in full field
Smearing + W-Term errors!
Errors due toPointing errors?
Errors due PBside-lobes?
17/21S. Bhatnagar: SASPO Meeting, CV, Nov. 9th 2010
Pointing SelfCal: Time dependent solutions
R-beam
L-beam
arcs
ec
Time
18/21S. Bhatnagar: SASPO Meeting, CV, Nov. 9th 2010
● EVLA polarization squint solved as pointing error (optical pointing error).● Squint would be symmetric about the origin in El-Az plane in the absence of antenna servo pointing errors.
● Pointing errors for various antennas detected in the range 1-7 arcmin.● Pointing errors confirmed independently via the EVLA online system.
[paper in preparation]
DD SelfCal algorithm: EVLA Data
R-beam
L-beam
Pointing errorR-beam
L-beam
Pointing error
● El-Az mount antennas● Polarization squint due to off-axis feeds - The R- and L-beam patterns have a pointing error of +/- ~0.06
● DoF used: 2 per antenna● SNR available for more DoF to model the PB shape
D
19/21S. Bhatnagar: SASPO Meeting, CV, Nov. 9th 2010
I/O load
• Near future data volume (0-1 years)• Recent data with the EVLA: 100-500 GB
• Next 5 years• 100X increase (in volume and effective I/O)
• Non-streaming data processing• Expect 20-50 passes through the data (flagging + calibration
+ imaging)– Effective data i/o: few TB
• Exploit data parallelism
• Distribute normal equations (SPMD paradigm looks promising)
• Deploy computationally efficient algorithms (‘P’ of SPMD) on a cluster
20/21S. Bhatnagar: SASPO Meeting, CV, Nov. 9th 2010
Computing challenges
• Significant increase in computing for wide-field wide-band imaging
• Correction of direction dependent terms• As expensive as imaging
• 1 TB effective I/O for calibrating and imaging a 100 GB data-set
• Run-time algorithm efficiency is an important parameter
• Run-time memory requirement
21/21S. Bhatnagar: SASPO Meeting, CV, Nov. 9th 2010
Near term future activities
• Re-factor existing code– Integration of MS-MFS and AW-Projection algorithms
– Use A-Projection for mosaicking (ALMA and EVLA)
– Allow use of arbitrary antenna PB (CASA/ARDG)
• Test wide-band wide-field imaging with EVLA
• Deploy on HPC platforms
• Test mosaicking with PB corrections
• Explore GPU processing
• Full-Stokes PB Corrections• Extend it for wide-band imaging
• Full Stokes Imaging
• Implement and test RFI flagging algorithms
• Pipeline processing using all the above for scientific projects
In progress/Programing
In progress+R&D
In progress/Programing
Programing/R&D?
R&D required <--
R&D required
Prog. + possibly R&D
Programming and R&D <--
R&D required