EOVSA Data Analysis Tutorial

Browsing and Obtaining EOVSA data

Browsing EOVSA data in RHESSI Browser

Currently the most convenient way for browsing EOVSA data is through the RHESSI Browser. First, check the "EOVSA Radio Data" box on the data selection area (top-left corner). Then select year/month/date to view the overall EOVSA dynamic spectrum. Note if a time is selected at early UTC hours (e.g., 0-3 UT), it will show the EOVSA dynamic spectrum from the previous day. Also note that EOVSA data were not commissioned for spectroscopic imaging prior to April 2017. An example of the overview EOVSA dynamic spectrum for 2017 Aug 21 is shown in the figure on the right.

The overview EOVSA dynamic spectra are from the median of the uncalibrated cross-power visibilities at a few short baselines, which are not (but a good proxy of) the total-power dynamic spectra. The effects of spatial information blended in the cross-power visibilities can be clearly seen as the "U"-shaped features throughout the day, which are due to the movement of the Sun across the sky that effectively changes the length and orientation of the baselines. Flare times can be easily seen in the EOVSA dynamic spectra, which usually appear as vertical bright features across many frequency bands. More information can be found on this page.

We are currently working on a pipeline to create quicklook full-disk images for implementation at the RHESSI Browser in a way similar as the RHESSI quicklook images. Please stay tuned.

Once you identify the flare time, you can find the full-resolution (1-s cadence) uncalibrated visibility files (in Miriad format) at this link. Each data file is usually 10 minutes in duration. Name convention is YYYYMMDD/IDBYYYYMMDDHHMMSS, where the time in the file name indicates the start time of the visibility data.

Calibrating EOVSA data

• Calibration: We are currently working on a pipeline in calibrating the visibility data. At this moment, please contact the EOVSA team if you wish to have calibrated visibility data of a specific event. In the near future, we envision the pipeline calibrated visibility data to be available for download on a regular basis.

• Self-calibration: For improving the quality of the imaging, self-calibration is usually needed. This is still a work-in-progress, but we have had some successful practice in self-calibrating some flare data. Please refer to this page for examples and detailed discussions on our current practice for self-calibrating EOVSA flare data.

In this tutorial, we will demonstrate steps for spectral imaging the self-calibrated visibility data for a C-class flare on 2017 Aug 21 at ~20:20 UT, followed by a tutorial on visualizing and analyzing the resulting spectral imaging cube. The visibility data can be downloaded from this link. If you are on our AWS cloud server (means for accessing the server are discussed in Section 3.1.1), it is located at /common/data/eovsa_tutorial/IDB20170821201800-202300.4s.slfcaled.ms

Analyzing EOVSA data

Software

We have developed two packages for EOVSA data processing and analysis:

• SunCASA A wrapper around CASA for synthesis imaging and visualizing solar spectral imaging data. More information about CASA can be found on NRAO's CASA website . Note, (Sun)CASA is ONLY AVAILABLE on UNIX-BASED PLATFORMS (sorry Windows users).
• GSFIT A IDL-widget(GUI)-based spectral fitting package called gsfit, which provides a user-friendly display of EOVSA image cubes and an interface to fast fitting codes (via platform-dependent shared-object libraries).

There are two approaches in accessing our software packages. One is through our Amazon AWS server (recommended for participants of the EOVSA tutorial at the RHESSI 18 Workshop). Another is to install them on your own machine. We discuss the first approach in Section 2.1, and the second in Section 2.2 (SunCASA) and 2.3 (GSFIT).

Using Software on AWS server

We use an Amazon AWS Lightsail server for testing purposes. The server has 2 CPUs, 8 GB RAM, and 160 GB SSD storage. It runs CentOS 7 (1901-01) Linux. Please limit your usage to LIGHTWEIGHT DATA PROCESSING ONLY.

NOTE: THE ACCOUNT IS ONLY INTENDED FOR THE EOVSA TUTORIAL, BUT *NOT* FOR CARRYING OUT ACTUAL DATA REDUCTION

• Obtain SSH Key from Bin Chen
• Put it under a secure location on your own machine.
• Follow remaining directions depending on your client machine.

Connecting via Linux / Mac

Recommend to use "~/.ssh" (create if it does not exist by "mkdir ~/.ssh").

• Edit the permission of ~/.ssh and the key (here I use ~/.ssh as the directory to place your key)

chmod 700 ~/.ssh
chmod 400 ~/.ssh/guest-virgo.pem

• Log on to test AWS server (password-less)

ssh -X -i ~/.ssh/guest-virgo.pem guest@virgo.arcs.az.njit.edu

Now you are connected to virgo.

Connecting via Windows (MobaXterm)

Recommend to use "Documents\MobaXterm\home\.ssh", which should exist if you have already installed the free MobaXterm[1].

• Create new session, click SSH, enter virgo.arcs.az.njit.edu for Remote host, guest for username.
• On advanced SSH settings tab, click Use private key, navigate to and select file guest_key.pem
• Close setup window and click the new sessions icon, which will log you in.

Startup SunCASA and sswIDL

Once the connection is setup, you will have access to SunCASA and GSFIT (included in the sswIDL installation). To not interfere with others (who share the same "guest" account), please create your own directory and work under it. For easier identification, please use the initial of your first name and your full last name as the name of your directory (here "bchen" is used as an example).

[guest@ip-172-26-5-203 ~]$ mkdir bchen
[guest@ip-172-26-5-203 ~]$ cd bchen

Enter SunCASA

[guest@ip-172-26-5-203 ~/bchen]$ suncasa

Enter sswIDL

[guest@ip-172-26-5-203 ~/bchen]$ sswidl

SunCASA Installation

Please click on the link above for details regarding installation of SunCASA on your own machine (only available on Unix-bases OS). This will take you to another page.

GSFIT Installation

Please click on the link above for details regarding installation of GSFIT on your own machine. This will take you to another page.

Spectral Imaging with SunCASA

Before Starting SunCASA

You will likely be running SunCASA from a working directory that has your data on it, or where you want your output to go. Warning: SunCASA does not like a directory that contains spaces in its path. If you have done your own installation as instructed above, then there should be an executable script called suncasa in your system path. This script will set up the required environment and run the version of SunCASA that it points to. EOVSA data is handled in CASA tables system, known as a Measurement Set (MS). The actual visibility data are stored in a MAIN table that contains a number of rows, each of which is effectively a single timestamp for a single spectral window and a single baseline. Within SunCASA, you will have access to a collection of tools that allow you to explore and utilize the new radio dynamic spectroscopic imaging data from EOVSA. You can open up a terminal, cd your working directory (e.g., ~/bchen/), and type

# in a terminal, outside of SunCASA:
cd yourworkdirectory
suncasa

Within SunCASA, you are using IPython to interact with the system. This does not mean extensive python experience is necessary. Basic Python interactions are straightforward, e.g., assigning parameters, importing modules, running functions.

Dynamic Spectrum and Imaging

Overview

This tutorial describes the making dynamic spectrum and imaging the EOVSA microwave data observed on August 21, 2017. The calibrated data set for the tutorial can be access on virgo. Please copy it over to you working directory.

## in SunCASA
!cp -r /common/data/eovsa_tutorial/IDB20170821201800-202300.4s.slfcaled.ms ./

Get Dynamic Sepctrum with SunCASA

The first module we introduce is dspec. This module allows you to generate a dynamic spectrum from an MS file, and visualize it. You can select a subset of data by specifying a time range, spectral windows/channels, antenna baseline, or uvrange. The selection syntax follows the CASA convention. More information of CASA selection syntax may be found in the above links or the Measurement Selection Syntax.

Figure 1: EOVSA cross power dynamic spectrum at stokes XX and YY

from suncasa.utils import dspec as ds
import matplotlib.pyplot as plt
## define the visbility data file
msfile = 'IDB20170821201800-202300.4s.slfcaled.ms' 
## define the output filename of the dynamic spectrum 
specfile = msfile + '.dspec.npz'  
##  antenna selection 
## leave it blank for selecting all baselines
bl = ''
## Spectral Windows and Channels selection
## leave it blank for selecting all spectral windows
spw = ''
## time range selection
## leave it blank for selecting the entire time interval
timeran = ''
## select baselines with a median length (0.15~0.5km)
uvrange = '0.15~0.5km'
## this step generates a dynamic spectrum and saves it to specfile
ds.get_dspec(vis=msfile, specfile=specfile, bl=bl, spw=spw, uvrange=uvrange)
## this plot the dynamic spectrum.
ds.plt_dspec(specfile, pol='XXYY')
## show the plot
plt.show()

Now you should have a popup window showing the dynamic spectrum. Hover your mouse over the dynamic spectrum, you can read the time and frequency information at the bottom of the window.

Imaging with SunCASA

Imaging EOVSA data involves image cleaning, as well as solar coordinate transformation and image registration. We bundled a number of these steps ino a module named qlookplot. Now let us start with making a radio image from the spectral window 5 (5.4 GHz).

Figure 2: EOVSA single band observation summary

## in SunCASA
from suncasa.utils import qlookplot as ql
msfile = 'IDB20170821201800-202300.4s.slfcaled.ms'
specfile = msfile + '.dspec.npz'  ## provide the dynamic spectrum data or it will generate a new one.
timerange = '20:21:10~20:21:30'  ## set the time interval
spw = '7'  ## select the spectral window 7
stokes = 'XXYY'   ## polarizations selection
restoringbeam = ['20arcsec']  ## force to use a circilar Gaussian as the restoring beam
ql.qlookplot(vis=msfile, specfile=specfile, timerange=timerange, spw=spw, stokes=stokes,restoringbeam = restoringbeam)

The resulted radio image is a 4-D datacube, which is saved as a fits file msfile + '.outim.image.fits' under your working directory.

SIMPLE  =                    T /Standard FITS                                   
BITPIX  =                  -32 /Floating point (32 bit)                         
NAXIS   =                    4                                                  
NAXIS1  =                  512/ Nx
NAXIS2  =                  512/ Ny                                             
NAXIS3  =                    1/  number of frequency                                           
NAXIS4  =                    2/  number of polarization

By default, qlookplot produces a full sun radio image (512x512 with a pixel size of 5"). If you know where the radio source is, you can make a partial sun image around the source by specifing the image center, pixel, and image size.

Figure 3: EOVSA single band observation summary

## in SunCASA
xycen = [375, 45]  ## image center for clean in solar X-Y in arcsec
cell=['2.0arcsec', '2.0arcsec'] ## pixel size
imsize=[128, 128]   ## x and y image size in pixels
fov = [200,200]  ## field of view of the zoomed-in panels in unit of arcsec
ql.qlookplot(vis, specfile=specfile, timerange=timerange, spw=spw, stokes=stokes,\
restoringbeam=restoringbeam,imsize=imsize,cell=cell,xycen=xycen,fov=fov)

Now, let's make a multi bands image.

Figure 4: EOVSA multi bands observation summary

## in SunCASA
xycen = [375, 45]  ## image center for clean in solar X-Y in arcsec
cell=['2.0arcsec', '2.0arcsec'] ## pixel size
imsize=[128, 128]   ## x and y image size in pixels
fov = [200,200]  ## field of view of the zoomed-in panels in unit of arcsec
spw = ['{}'.format(ll) for ll in range(1,31)]
clevels = [0.5, 1.0]  ## the contour levels of the transparent contours of the radio maps.
calpha=0.35  ## the alpha blending value
ql.qlookplot(vis, specfile=specfile, timerange=timerange, spw=spw, stokes=stokes,\
restoringbeam=restoringbeam,imsize=imsize,cell=cell,xycen=xycen,fov=fov,clevels=clevels,calpha=calpha)

The output fits file is saved to msfile + '.outim.image.fits' under your working directory.

SIMPLE  =                    T / conforms to FITS standard                      
BITPIX  =                  -64 / array data type                                
NAXIS   =                    4 / number of array dimensions                     
NAXIS1  =                  128                                                  
NAXIS2  =                  128                                                  
NAXIS3  =                   30                                                  
NAXIS4  =                    2  

Spectral Fitting with GSFIT

GSFIT GUI Application

The GSFIT GUI application may be launched as follows

IDL> gsfit [,nthreads]

where nthreads is an optional argument that indicates the number of parallel asynchronous threads to be used when performing the fit tasks. By default, GSFIT launches with only one thread, but the user may interactively add or delete threads as needed at the run-time up to the number of CPUs available on the system (Note, if you are working on the AWS server, please use only one thread). After some delay while the interface loads, the GUI below should appear.

• 

  GSFIT GUI appearance on Windows OS

• 

  GSFIT GUI appearance on Linux/Mac OS

A detailed description of the GSFIT functionality is provided in the page linked below.

GSFITCP Batch Mode Application

GSFITCP is the command prompt counterpart of the GSFIT GUI microwave spectral fitting application. Once started, GSFITCP is designed to run in unattended mode until all fitting tasks assigned to it are completed and log on the disk in an user-defined *.log file, the content of which may be visualized using the GSFITVIEW GUI application. When run remotely on an Linux/Mac platform, the GSFITCP may be launched on a detached screen, which allows the remote user to logout without stopping the process in which GSFITCP runs.

GSFITCP is launched using the following call:

IDL> gsfitcp, taskfile, nthreads, /start

where taskfile is a path to a file in which a GSFIT task has been previously saved, as explained in the GSFIT Help page, nthreads is an optional argument indicating the number of parallel asynchronous threads to be used, and the optional keyword /start, if set, requests immediate start of the batch processing.

A detailed description of the GSFITCP functionality is provided in the page linked below.

GSFITVIEW GUI Application

The GSFITVIEW GUI application may be launched as follows

IDL> gsfitview [,gsfitmaps]

where the optional gsfitmaps argument is either the filename of an IDL *.sav file containg a GSFIT Parameter Map Cube structure produced by the GSFIT or GSFITCP applications, or an already restored such structure.

• 
• 

A detailed description of the GSFITVIEW functionality is provided in the page linked below.