ALBIUS: Achievements in reporting period: 2010 Q4/2011 Q1

During the reporting period, ALBiUS partners had one teleconference meeting per quarter: November 2010 and March 2011.

List of working documents

ASTRON: Oleg Smirnov published 3 papers on Calibration and Direction dependent effects 1,2,3

ESO: Dirk Petry wrote a number of reports about CASA tests.

JIVE: Fringe Fitting in Casa design document, Fring fitting algorithms and Ian Stewart's report on fringe fitting.

Main Activities during

ASTRON: To correct for direction-dependent effects (like the LOFAR beam) a script has been developed that creates and deconvolves the image using facets. The DDE-correction is calculated for the center of the facet and applied to the entire facet. It works well and produced some good images. However, it is quite slow.
The LOFAR MeasurementSet has been extended with some tables containing all information necessary for the beam calculation.
A LOFAR task force has been started to investigate if direction-dependent effects due to the ionosphere can also be corrected for using the A-propjection method. Support for shapelets as a source model has been added to the LOFAR software. It makes it possible to model a strong source like Cyg-A more compact and accurate.

ESO: The translation of the ALMA response images (obtained from TICRA) into correct CASA images was finalised and the responses for the three ALMA antenna types was put into a coherent scheme. For this purpose, a unified general access scheme to interferometer antenna responses patterns in CASA (AntennaResponses table) was designed and implemented.
With Sanjay Bhatnagar from NRAO, the ALMAAperture class for using the antenna response patterns to correct for direction dependent effects in imaging was designed and implemented. Tests are ongoing. Intermediate result is that a preliminary version of the ALMA Antenna Responses is now in the release branch of CASA and will go out with the 3.2 release in May.

UOXF: Distributed Processing
Currently on effort has been done. There is a person in ASTRON who did something similar, so might be an option to join forces here.

Data Inspection
- Work in progress on metadata inspection. No issues.
- Work done in visibility quality control. No issues.

Data Excision
- Acquired knowledge about UVFITS to MS flagging, though not been implemented into software/concepts.

Testing novel calibration algorithm for quality control. This effort will make use of GMRT data in combination with the GMRT pipeline. The result of will be written up in a report and could result into a module which can be used in ParselTongue. The possible output of the modules will be Telescope based and could be evaluated within the Metadata inspection task.

A first software module of the calibration code has been developed (Dulwich) and is currently implemented to work within ParselTongue and the GMRT pipeline (Kloeckner). First test has been done, but there are still some minor issues related to data modelling in AIPS. Closure phase plots will be developed in order to evalutate the correctness of the calibration modules.


New implementation of Global Fringe Fitting algorithm: NRAO has retained only a facilitory role in the fringe fitting development after handing this deliverable over to JIVE. NRAO hosted the visit of Stephen Bourke and Ian Stewart in Socorro in February 2011. A full report on this work will be provided by JIVE. NRAO will be happy to host a second visit of fringe fitting developers this year if deemed useful.

Software for mosaic imaging including primary beam correction: The delivery date for this milestone was Month 25 of RadioNet FP7, or February 2011. This deadline was not met, but considerable work has been made toward the goal. The key components are contained within the A-projection algorithm as described below. Code supporting A-projection will be included in CASA version 3.2, which is to be released late April or early May 2011. This code will not be directly accessable by users at this point but will be for CASA version 3.3 to be released sometime around October 2011. It is anticipated that both the spirit and the word of the goals will be fully met at this time.
Most of the work done in this cycle in the area of algorithms to correct for various Primary Beam (PB) effects (effects of wide-band sensitivity pattern, time-dependent gain variations due to rotation of the PB and pointing errors, and PB effects for heterogeneous arrays like ALMA) fall in the following categories:
1. Implementation of the software framework for the A-Projection approach to allow handling of heterogeneous arrays
2. Implementing the components of this framework for ALMA to use simulated antenna aperture illumination patterns.
3. Begin prototyping work on multi-threaded gridding utilizing multi-core CPUs resources to improve run-time performance.
Prior to re-factoring of the software framework, the implementation of the A-Projection algorithm supported only EVLA primary beams. Code required to include PBs for other telescopes, in particular ALMA, was re-factored to allow inclusion of other PBs such that only a single telescope-specific specialization of a software component needs to be written. This component for the EVLA was implement and the software framework was regressively tested against existing data from the EVLA. The ALMA-specific component has also been written by Dirk at ESO and is pending software testing. Some more work on this front for the extra bookkeeping for heterogeneous arrays might still be required to fully integrate this into the framework. Further work is planned when Dirk visits us here.
The technique for correcting antenna pointing errors utilizes the A-Projection algorithm and has a relatively high computing foot print. Work on corrections for the antenna pointing errors will follow after the work on integration of ALMA PBs and the work for deploying the A-Projection algorithm on the HPC platform.
In support of efficient use, effort towards parallelization has continued on 2 fronts: multi-process (cluster computing) and threaded (multi-core on a single machine).
Multi-process imaging for continuum and spectral cube was achieved last year. This year work on this has been refinements and bug fixing. The work this year was focussed on dealing with data-parallel optimization for problems that require minimal inter-process communication. Imaging with multi-process parallelization will work on single or multiple datasets. This infrastructure has lead to an easy path for implementing parallelization of different modules of a data reduction pipeline (e.g., flagging, calibration application or continuum subtraction) by distributing the work on different datasets to different processes.
Multi-threaded parallelization had already been applied to the time-consuming gridding process of continuum imaging. We have been experimenting with multi-threaded approach for Multiscale clean and a first version is available using OpenMP. Work is being done on non-blocking multi-threaded I/O access and multi-threaded gridding of data in imaging. A-Projection, and in general techniques for wide-band imaging, require more computing compared to standard techniques for narrow band imaging. To solve the problem of higher computing requirements, the current efforts for parallelization of CASA uses the approach of multiple processes per node on a multi-node cluster. The memory footprint for this scales linearly with the number of processes and is not indefinitely scalable, motivating parallelization across many computers within a cluster.
On the mosaicing front, we passed for the first time real interferometric on-the-fly mosac data from ALMA through CASA. The code was shown to work.


Interoperability - The activity on translating AIPS calibration tables (solution, bandpass, and calibration) to Casa calibration tables was continued. The earlier proof of concept utilities were consolidated into a single tool and a Casa task interface was added. The Casa task makes use of earlier work on also conducted for this activity - the unified Casa/ParselTongue environment.

The software has been tested and verified with VLA and WSRT data, and partially verified for EVN data. The latter being a slightly more complicated test case due to the interdependency between the FITS loader, the flag importer and the calibration transfer.

Global Fringe Fitting - Substantive work commenced on Global Fringe Fitting in January 2011. Although in view of the short remaining time available to complete this package, the formal objectives had been scaled back to just the production of a report, it is nevertheless felt that it may still be possible to make some inroads into the initial desirables of introducing some GFF capability into CASA on the one hand and exploring some new and extended algorithms on the other.
Near the start of the work period, Stephen Bourke and Ian Stewart visited the VLAOC at Socorro. The aims of this visit were information transfer to Stephen and Ian on the one hand and discussion and agreeing on a GFF interface with CASA on the other. Both these objectives were successfully met.
Since this Socorro visit, Stephen has been working mostly on the interface with CASA. He has written a simple framework fringe-fitting solver along the lines agreed at Socorro. This has lately been tested with real data and been found to perform satisfactorily. Ian has been investigating a new algorithm, which performs a fast linear fit to the imaginary part of visibilities which have been coarsely phase-flattened, and has extended the familiar Fourier-transform algorithm to return uncertainties in the returned values of delay and rate.

Implemented a rate solver in Casa which uses the FFT method to estimate delay rates. I have implemented baseline stacking code, which exploits phase closure properties of visibilities to stack equivalent 'pseudo' baselines to gain sensitivity. This is most beneficial on homogeneous arrays which lack a big dish to boot strap.

UCAM: Joern Geisbuesch has left and Cambridge didn't have the PDRA effort. A new person has been appointed: Samuel George, who will start in May. His expertise will enable to move forward very quickly on the deliverable. However since the submission of the interim deliverable there has been very little progress on the task But Cambridge will meet the deliverables by the end of this year.


- Migrated multi-rate filter to DiFX 2.
- EVN OH observation of Cyg A, NGC 1068 arrived at Bonn correlator and is in fringe search. For testing multi-rate filter performance in a real observation with RFI (GLONASS).

- Test data from a geodetic S-band experiment correlated.

- Westerbork APERTIF correlation matrices received from Wim van Capellen

- Algorithm development for beamformer with Kesteven algorithm for RFI mitigation progressing.

- Synthetic data was generated for controlled testing of the algorithm.

BORD: Goal of Astrometry task is to combine group delays and phase delays for astrometric applications. This includes devising new observing strategies. MODEST software package identified as suitable for this purpose.

- Implement and test procedure to simulate group delays with MODEST
- Compare simulated vs theoretical group delays
- Implement elevation-dependent tropospheric noise and analyze results
- Implement procedure to simulate phase delays with MODEST
- Begin testing procedure for phase delays

Meetings attended by people involved

ASTRON: In October Ger van Diepen attended the XLDB conference in Stanford. In that same trip he visited NRAO in Socorro to work with Sanjay Bhatnagar on CASA.

ESO: 1. CASA developers’ meeting, Socorro May 2010; 2. Calibration workshop, the Netherlands August 2010

JIVE and NRAO: Socorro fringe fitting meeting, 26 January - 11 February.

Problems / Issues

JIVE: In the Interoperability subtask, producing tables in conformance with the Casa calibration table specification is not adequate to ensure compatibility. It can be difficult to fully reverse engineer Casa's requirements for correct treatment of tables.

- Finish implementation/testing of procedure for simulating phase delays
- Combine simulated group delays and phase delays
- Test observing strategies
- Get in touch with Spanish group (Valencia) to discuss/compare results

Red flags - major problems

UOXF: Only minor development on image quality control and so far we have nobody working on the subtask.

Forward Look

ASTRON: To improve the performance of DDE corrections the A-projection method seems very promising. In May a few people will go to NRAO in Socorro to work with Sanjay Bhatnagar on the implementation of A-projection for LOFAR.

ESO: 3 months: Preliminary version of the ALMA Antenna Responses will be in the release branch of CASA and will go out with the 3.2 release in May.
6 months: Tests.

JIVE: Interoperability work will briefly be resumed in Q2 2011 for testing with the latest Casa release, and reporting.
The development of global fringe fitting algorithms will continue until the end of April. Casa implementation will continue until later in the year.

Expected Milestones

JIVE: Interoperability report and software finalisation in Q2.
Global Fringe Fitting implementation in Python, May 2011. Casa FFT Delay/rate solutions, Q2 2011. Baseline stacking and application of solutions Q3 2011.

MPIfR: Delivery of all deliverables is expected by end of 2011.

Number of Persons working in JRA

ESO: 4 Persons (Person-hours: Q2, Q3, Q4: 230 per quarter, Q1 2011: 230.)

UOXF: Total person months spend so far up to the 30.03.2011: (Kloeckner 11 PM, Dulwich 0.5 PM)

JIVE: 2 Persons (Bourke and Stewart)

BORD: Laurent Chemin (100%) – contract goes until 15 April 2012, Patrick Charlot (~10%). Must get an official paper stating that RadioNet is extended until 30 June 2012 in order to be able to spend RadioNet funding beyond 31 December 2011.

MPIfR: Jan Wagner (plus a small fraction of Alan Roy.)

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