1 Lites CSAC SOT #17 Meeting, NAOJ, April Solar-B FPP The NCAR/HAO Community Spectro-Polarimetric Analysis Center (CSAC) Bruce W. Lites

2 Lites CSAC SOT #17 Meeting, NAOJ, April Solar-B FPP What is CSAC? Repository for analysis software for spectro-polarimetric data Community involvement/community access Full range of analysis: –Calibration –Inversions –Ambiguity resolution –Data visualization Goals: –Tested, transportable, documented code –Conformation to modern software standards –Computational efficiency

3 Lites CSAC SOT #17 Meeting, NAOJ, April Solar-B FPP Why CSAC? Spectro-Polarimetric (SP) data has the highest information content: Allows comprehensive, quantitative measures of B Permits extraction of line-of-sight gradients BUT: SP Data is intrinsically more difficult to reduce Higher information content means more detailed analysis The problem of the past: Analysis codes have been cumbersome, opaque, not easily ported to other systems, and not particularly well documented CSAC aims to remedy these problems

4 Lites CSAC SOT #17 Meeting, NAOJ, April Solar-B FPP Why CSAC? Widespread interest in spectro-polarimetry: many polarimeters are new and under-development.

5 Lites CSAC SOT #17 Meeting, NAOJ, April Solar-B FPP Some CSAC Priorities 1.Data Reduction Routines: Develop software for flat-fielding, polarization calibration, merging, rectification, fringe removal, etc. to prepare data sets for subsequent inversion. 2.Milne-Eddington Inversion: This is the workhorse of analysis of SP data to extract the magnetic field vector (and other associated properties of the magnetized atmosphere). 3.LILIA Inversion: Develop standardized, portable software based upon the SIR (Stokes Inversion by Response functions) procedure. This technique allows for variation of parameters along the line-of-sight. 4.Rapid Inversion Techniques: New techniques such as principal components analysis, neural networks, support vector machines offer meaningful inversions at a very large increase in speed. 5.Ambiguity Resolution: CSAC will serve codes for resolution of the 180º azimuth ambiguity. 6.Data Visualization: The AZAM utility, as well as other methods for visualization, will be maintained by CSAC.

6 Lites CSAC SOT #17 Meeting, NAOJ, April Solar-B FPP A More Comprehensive List of CSAC Inversion Methods

7 Lites CSAC SOT #17 Meeting, NAOJ, April Solar-B FPP CSAC Data Reduction Routines Most SP data has a lot in common: Dual beam polarimeters require merging Flat-field determination requires care because of spectral lines Spectral skew, curvature are common attributes Polarimetric calibration variations over the spectral field-of-view CSAC has developed codes for data reduction for several instruments (DLSP, Swedish SP, and now Solar-B) Procedures both in IDL and FORTRAN FORTRAN routines much faster, allow for real-time processing and calibration Data-specific parameters external to the code Simplification of the calling process relieves the user of complex data processing sequences Commonality among instruments of processed data structure

8 Lites CSAC SOT #17 Meeting, NAOJ, April Solar-B FPP Milne-Eddington Inversion Code Designed for parallel processing via GRID architecture Unlike many problems, the inversion of Stokes data consists of many separate but identical computational tasks that require no interaction among them This is known as a “scatter-gather” computing problem, amenable to GRID computation The GRID consists of a heterogeneous array of loosely interconnected individual nodes sharing common resources In our case the interconnect is via a network (LAN, or WWW) Code is named Grid Inversion Method by Milne Eddington (GIMME)

9 Lites CSAC SOT #17 Meeting, NAOJ, April Solar-B FPP Inversion Components GIMME serves as a model for subsequent, more sophisticated CSAC inversion codes. It consists of 4 components: 1.The Inversion Kernel (IK): A set of libraries of codes (mainly C, C++) to perform the actual inversion computations 2.The Grid Inversion Server (GIS): An executable, run on the separate nodes of the Grid, that listens for incoming commands from the Client to run inversions, then run the IK libraries for such commands 3.The Grid data server (GDS): An executable that accesses requests for slices of a data cube, then serve them to the GIS. If accessed locally, it is a UNIX library. If remote, uses an OPEnDAP server. 4.The Grid client (GC): A web server application that allows the user to initiate inversions of either local or remote data sets.

10 Lites CSAC SOT #17 Meeting, NAOJ, April Solar-B FPP Stokes Data Inversion Typical SP data is 4-dimensional: Spatial slit scan direction (x) Spatial dimension along slit (y) Wavelength (λ) Polarization (I,Q,U,V)

11 Lites CSAC SOT #17 Meeting, NAOJ, April Solar-B FPP Data Passed by GDS to GIS The individual unit of inversion is the set of Stokes spectra (at right) One or more of these may be passed to the GIS The GDS accesses the entire data volume, and selects the requested slice, then passes it to the various GIS Typically, each GIS receives data from one slit position (one x-position, all y-positions)

12 Lites CSAC SOT #17 Meeting, NAOJ, April Solar-B FPP Grid Topology Example: 2 local GIS running under Unix sockets 2 remote GIS running under TCP/IP 1 local GDS running under NFS 1 remote GDS running under TCP/IP If data sits at llnl.gov: all 4 GIS will be used If data sits at ucar.edu: only 2 local GIS may be used to access these data

13 Lites CSAC SOT #17 Meeting, NAOJ, April Solar-B FPP Example of Grid Operations The Client is a web server. For highest efficiency it resides in proximity to the Grid Inversion Servers so that it may communicate rapidly and receive results.

14 Lites CSAC SOT #17 Meeting, NAOJ, April Solar-B FPP Standards for the CSAC Library of Analysis Tools Codes are highly transportable (written in C, C++), callable from IDL Supported under Linux, Solaris Efficient coding, appropriate for parallel architecture Well documented, commented, and tested Flexibility to accommodate data from a wide variety of instruments Standardized input/output Standards for presentation in solar coordinates Filters provided to convert input data from major instruments (Solar-B, DLSP, SOLIS, etc.) Codes maintained at a HAO/NCAR Examples of input/output data provided Open source for user modification, experimentation, and community input Online access to all analysis tools User forum for suggested modifications, additions

15 Lites CSAC SOT #17 Meeting, NAOJ, April Solar-B FPP The AZAM Utility

16 Lites CSAC SOT #17 Meeting, NAOJ, April Solar-B FPP The AZAM Utility Interactive, manual resolution of the 180º azimuth ambiguity Flexible display of inversion parameters Color images Arrows Blinking images against one another Contour plots Interactive display of data: images, spectral profiles, And much more………………

17 Lites CSAC SOT #17 Meeting, NAOJ, April Solar-B FPP Advanced Inversion Methods Measured electric current density at heights 200, 650, and 1600 km – Socas-Navarro 2005, ApJ 633, L57 Advanced inversion techniques allow extraction of the field vector from the photosphere into the chromosphere from simultaneous measurements of photospheric lines and the Ca II IRT lines

18 Lites CSAC SOT #17 Meeting, NAOJ, April Solar-B FPP CSAC Outlook for the Coming Year 1.Finish GIMME Milne-Eddington Inversion, prepare for analysis of Solar- B data 2.Implement Artificial Neural Network initialization for GIMME 3.Implement LILIA detailed inversion 4.Generalize AZAM to accept data from GIMME (i.e., from any data source) 5.Implement the simulated annealing azimuth ambiguity resolution for automatic processing 6.Host a community workshop to address community needs 7.Sponsor graduate student visits