EOVSA Data Analysis Tutorial
Browsing and Obtaining EOVSA data
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: Calibration of the EOVSA data is an involved process. We are currently working on a semi-automatic pipeline for calibrating the visibility data. At this moment, however, please contact the EOVSA team if you wish to have calibrated visibility data for 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 events. Please refer to Self-Calibrating Flare Data 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 (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 (the Common Astronomy Software Applications package) for synthesis imaging and visualizing solar spectral imaging data. CASA is one of the leading software tool for "supporting the data post-processing needs of the next generation of radio astronomical telescopes such as ALMA and VLA", an international effort led by the National Radio Astronomy Observatory. The current version of CASA uses Python (2.7) interface. More information about CASA can be found on NRAO's CASA website . Note, CASA is available ONLY on UNIX-BASED PLATFORMS (and therefore, so is SunCASA).
- 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 (Recommended for this Tutorial)
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_virgo.pem
- Close setup window and click the new session's icon, which will log you in.
Startup SunCASA and sswIDL
Once you are connected to virgo, 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
To enter SunCASA
[guest@ip-172-26-5-203 ~/bchen]$ suncasa
To 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
Preparation
This tutorial uses EOVSA observation of a C-class flare that occurred on August 21, 2017. To reduce the amount of data for this tutorial, the time resolution has been reduced by a factor of 4, to 4 s per sample. The actual time resolution available is 1 s. The calibrated and self-calibrated dataset for the tutorial can be downloaded and accessed on Virgo. If you are on Virgo, please copy it over to your own working directory that you created earlier under the guest account (e.g., ~/guest/bchen/).
cd yourworkdirectory cp -r /common/data/eovsa_tutorial/IDB20170821201800-202300.4s.slfcaled.ms ./
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. To start SunCASA, use:
suncasa
Within SunCASA, you are under the IPython environment. Everything you know about (I)Python should be applicable here. The installation comes with frequently used packages including Matplotlib, Numpy, SciPy, AstroPy, SunPy. However, it is not very intuitive to add (compatible) Python packages within (Sun)CASA. If you need some specific packages for your analysis, and it does not require direct interaction with (Sun)CASA, we recommend you to use the standard Python environment. On Virgo, we have installed Anaconda 3, which can be accessed by, e.g., "ipython"
Cross-Power Dynamic Spectrum
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.
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'
## select relatively short baselines within a length (here I use 0.15~0.5km),
## and take a median cross all of them (with the domedian parameter)
## alternatively, you can use the "bl" parameter to select individual baseline(s)
uvrange = '0.15~0.5km'
## this step generates a dynamic spectrum and saves it to specfile
ds.get_dspec(vis=msfile, specfile=specfile, uvrange=uvrange, domedian=True)
## Other optional parameters are available for more selection criteria
## such as frequency range ("spw"), and time range ("timeran")
## Use "ds.get_dspec?" to see more options
## define the polarizations to show (here I use XX and YY)
pol='XXYY'
## The following command displays the resulting cross-power dynamic spectrum
ds.plt_dspec(specfile, pol=pol)
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.
Quick-Look Imaging
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, allowing users to generate a observing summary plot showing the cross power dynamic spectrum, GOES light curves and EOVSA quick-look images. Now let us start with making a summary plot of EOVSA image at the spectral window 5 (5.4 GHz).
## in SunCASA from suncasa.utils import qlookplot as ql msfile = 'IDB20170821201800-202300.4s.slfcaled.ms' ## provide the dynamic spectrum data or it will generate a new one. specfile = msfile + '.dspec.npz' ## set the time interval timerange = '20:21:10~20:21:30' ## select the spectral window 5 spw = '5' ## select stokes XX stokes = 'XX' ## turn off AIA image plotting, default is True plotaia = False ## force to use a circular Gaussian as the restoring beam restoringbeam = ['20arcsec'] ql.qlookplot(vis=msfile, specfile=specfile, timerange=timerange, spw=spw, \ stokes=stokes,restoringbeam = restoringbeam, plotaia=plotaia)
Feel free to explore by adjusting the above parameters, e.g. use a different timerange and/or a range of spw. With qlookplot, it is easy to engage solar data from SDO/AIA in the summary plot. Setting plotaia=True in the qlookplot command will download SDO/AIA data at the given time to current directory and add it to the summary plot.
## in SunCASA plotaia = True calpha=1.0 ## the alpha blending value ql.qlookplot(vis=msfile, specfile=specfile, timerange=timerange, spw=spw, \ stokes=stokes,restoringbeam = restoringbeam, plotaia= plotaia, calpha=calpha)
The resulting radio image is a 4-D datacube (in solar X-pos, Y-pos, frequency, and polarization), which is, by default, saved as a fits file msfile + '.outim.image.fits' under your working directory. The name of the output fits file can be specified using the "outfits" parameter.
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 solar image around the source by specifying the image center, pixel size, and image size.
## 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 = [100,100] ## field of view of the zoomed-in panels in unit of arcsec ql.qlookplot(vis=msfile, specfile=specfile, timerange=timerange, spw=spw, stokes=stokes,\ restoringbeam=restoringbeam,imsize=imsize,cell=cell,xycen=xycen,fov=fov,calpha=calpha)
Next, we will make images for every single spectral window in this data set (from spw 1 to 30, spw 0 is in the ms, but is empty).
## 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 = [100,100] ## 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 ## now tune down the alpha
ql.qlookplot(vis=msfile, 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
Batch-Mode Imaging
This section is for interested users who wish to generate FITS files with full control on all parameters being used for synthesis imaging. We provide one example SunCASA script for generating 30-band spectral imaging maps, and another for iterating over time to produce a time series of these maps.
Producing a 30-band map cube for a given time
An example script can be found at this Github link. If you are on the AWS server Virgo, it is under /common/data/eovsa_tutorial/imaging_example.py. First, download or copy the script to your own working directory and cd to your directory.
cd your_working_directory cp /common/data/eovsa_tutorial/imaging_example.py ./
Second (optional), change inputs in the following block in your copy of the "imaging_example.py" script and save the changes. This block has definitions for time range, image center and FOV, antennas used, cell size, number of pixels, etc.
### in "imaging_example.py", look for this block near the beginning ### ################### USER INPUT GOES IN THIS BLOK ######################## vis = 'IDB20170821201800-202300.4s.slfcaled.ms' # input visibility data trange = '2017/08/21/20:21:00~2017/08/21/20:21:30' #select the time range for imaging (averaging) xycen = [380., 50.] # define the center of the output map, in solar X and Y. Unit: arcsec xran = [280., 480.] # plot range in solar X. Unit: arcsec yran = [-50., 150.] # plot range in solar Y. Unit: arcsec antennas = '' # Use all 13 EOVSA 2-m antennas by default. If some antenna is no good, drop it in this selection npix = 256 # number of pixels in the image cell = '1arcsec' # pixel scale in arcsec pol = 'XX' # polarization to image, use XX for now pbcor = True # correct for primary beam response? outdir = './images' # Specify where you want to save the output fits files outimgpre = 'EO' # Something to add to the output image name #################################################################################
Then, run the script in SunCASA by
execfile('imaging_example.py')
The output fits images are saved under outdir. The naming conversion is outimgpre + YYYYMMDDTHHMMSS.SSS_S##.fits, where ## is the frequency band index number. See below for an example:
CASA <##>: ls ./images EO20170821T202115.000_S01.fits EO20170821T202115.000_S07.fits EO20170821T202115.000_S13.fits EO20170821T202115.000_S19.fits EO20170821T202115.000_S25.fits EO20170821T202115.000_S02.fits EO20170821T202115.000_S08.fits EO20170821T202115.000_S14.fits EO20170821T202115.000_S20.fits EO20170821T202115.000_S26.fits EO20170821T202115.000_S03.fits EO20170821T202115.000_S09.fits EO20170821T202115.000_S15.fits EO20170821T202115.000_S21.fits EO20170821T202115.000_S27.fits EO20170821T202115.000_S04.fits EO20170821T202115.000_S10.fits EO20170821T202115.000_S16.fits EO20170821T202115.000_S22.fits EO20170821T202115.000_S28.fits EO20170821T202115.000_S05.fits EO20170821T202115.000_S11.fits EO20170821T202115.000_S17.fits EO20170821T202115.000_S23.fits EO20170821T202115.000_S29.fits EO20170821T202115.000_S06.fits EO20170821T202115.000_S12.fits EO20170821T202115.000_S18.fits EO20170821T202115.000_S24.fits EO20170821T202115.000_S30.fits
From this point, you can use your favorite language (SSWIDL users: fits2map.pro would work on these) to read the fits files and plot them. The last block of the example script uses SunPy.map to generate the plot shown on the right.
Producing a time series of 30-band maps (a 4-d cube)
An example script can be found at this Github link. If you are on the AWS server Virgo, it is under /common/data/eovsa_tutorial/imaging_timeseries_example.py. Caution: This script is very computationally intensive. Please do not try to run this script on the AWS server Virgo, as it has limited resources that everyone share during the tutorial.
cd your_working_directory cp "pathtoyourscript"/imaging_timeseries_example.py ./
Similar as the previous script, change inputs in the following block of your copy of the "imaging_timeseries_example.py" script and save the changes.
### in "imaging_example.py", look for this block near the beginning ### ################### USER INPUT GOES IN THIS BLOK ######################## vis = 'IDB20170821201800-202300.4s.slfcaled.ms' # input visibility data specfile = vis + '.dspec.npz' ## input dynamic spectrum nthreads = 1 # Number of processing threads to use overwrite = True # whether to overwrite the existed fits files. trange = '' # select the time range for imaging, leave it blank for using the entire time interval in the data twidth = 1 # make one image out of every 2 time integrations xycen = [380., 50.] # define the center of the output map, in solar X and Y. Unit: arcsec xran = [280., 480.] # plot range in solar X. Unit: arcsec yran = [-50., 150.] # plot range in solar Y. Unit: arcsec antennas = '' # default is to use all 13 EOVSA 2-m antennas. npix = 128 # number of pixels in the image cell = '2arcsec' # pixel scale in arcsec pol = 'XX' # polarization to image, use XX for now pbcor = True # correct for primary beam response? grid_spacing = 5. * u.deg # spacing for plotting longitude and latitude grid in degrees outdir = './image_series/' # Specify where you want to save the output fits files imresfile = 'imres.npz' # File to write the imageing results summary outimgpre = 'EO' # Something to add to the image name #################################################################################
Then, run the script in SunCASA by
execfile('imaging_timeseries_example.py')
The output fits images and a summary file imresfile are saved under "outdir" (in this example "./image_timeseries"). The naming conversion of output fits images is the same as the previous section. The summary yields the time, frequency, and path to every image.
CASA <#>: imres = np.load(outdir + imresfile)['imres'][0]
CASA <#>: for k in imres.keys(): print(k,imres[k][0])
('EndTime', '2017-08-21T20:18:04.500') ## End time of clean for this particular FITS file
('Freq', '2.9296875') ## Central frequency in GHz
('ImageName', './image_series//EO20170821T201800.500_S01.fits') ## Path to the output FITS file
('BeginTime', '2017-08-21T20:18:00.500') ## Start time of clean for this Particular FITS file
('Succeeded', True) ## whether or not clean was successful
The last block of the example script uses SunPy.map to generate a series of plots and wraps them as a javascript movie.
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.
GSFIT Help
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.
GSFITCP Help
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.