EOVSA Data Products

Welcome to the EOVSA data products documentation. EOVSA observes the full disk of the Sun at all times when the Sun is >10 degrees above the local horizon, which is season dependent and ranges from 7-12 hours duration centered on 20 UT. During January, coverage will be 16-24 UT daily, 7 days/week. Like any radio interferometer, the fundamental measurement for imaging is the correlated amplitude and phase between each pair of antennas, which is called a “complex visibility.” EOVSA’s 13 antennas form 78 such visibilities at any frequency and instant of time, i.e. 78 measurements of the spatial Fourier transform of the solar brightness distribution. EOVSA records these visibilities at 451 science frequency channels each second, in four polarization products, as well as additional total flux measurements from each individual antenna. These data are then processed through a pipeline processing system (the block diagram in Figure 1 shows the data flow in the pipeline). One of the outputs of the pipeline is a visibility database in a widely used open-standard format called a CASA measurement set (or “ms”; CASA is the Common Astronomy Software Applications package used by many modern interferometer arrays). Many different CASA ms’s can be created from the raw visibility data by selecting time ranges, frequencies, integration times, polarizations, and so on.

We deliver the radio interferometry data on the following three levels:

Level 0 - Raw visibility data from the instrument

As outlined in Figure 1, the real-time pipeline creates raw data products in the left-hand column labeled Level 0. This includes observations of cosmic sources for phase calibration, and gain and pointing observations required for total power calibration.

raw full resolution visibility database

EOVSA full resolution visibility database can be retrieved from the following page:

http://www.ovsa.njit.edu/fits//IDB/

raw 1-min averaged visibility database

EOVSA 1-min averaged visibility database can be retrieved from the following page:

http://www.ovsa.njit.edu/fits/UDB/

Level 1 - calibrated visibility data

After applying calibration and other preliminary processing to level 0 data, we create the CASA ms’s in the second column in Figure 1, labeled Level 1. These visibility data have all of the required content to produce Level 2 images and spectrogram data in standard FITS format. We provide a set of standard ms’s for each day (red boxes in Figure 1), for use by researchers who wish to start with visibility data, while the full-resolution, raw visibility data are made available through links (TBD) to our server.

CASA Event ms

TBD

CASA 1-min averaged ms

EOVSA 1-min averaged visibility data in CASA ms format can be retrieved from the following page:

http://www.ovsa.njit.edu/fits/UDBms_slfcaled

Level 2 - Images and spectrogram data in standard FITS format

Most users, however, will prefer to work with spectrogram (frequency-time) and image data, which are also outputs of the pipeline system shown in Figure 1 (orange boxes). Spectrograms are provided as standard FITS tables containing the frequency list, list of times, and data in both total power and a sum of amplitudes over intermediate-length baselines (cross power). Likewise, image data products are in FITS format with standard keywords and are converted into the Helioprojective Cartesian coordinate system compatible with the World Coordinate System (WCS) convention, along with correct registration for the spatial, spectral, and temporal coordinates. Both the spectrogram and image data products are calibrated properly and have physical radio intensity units (sfu for spectrograms and brightness temperature for radio images).

List of Level 2 data products

category	data product	name
Dynamic Spectrum	All-day TP spectrum	EOVSA_TPall_yyyymmdd.fts
	All-day XP spectrum	EOVSA_XPall_yyyymmdd.fts
Image
	Synoptic 1.4 GHz image	eovsa_yyyymmdd.spw00-01.tb.disk.fits
	Synoptic 3.0 GHz image	eovsa_yyyymmdd.spw02-05.tb.disk.fits
	Synoptic 4.5 GHz image	eovsa_yyyymmdd.spw06-10.tb.disk.fits
	Synoptic 6.8 GHz image	eovsa_yyyymmdd.spw11-20.tb.disk.fits
	Synoptic 10.2 GHz image	eovsa_yyyymmdd.spw21-30.tb.disk.fits
	Synoptic 13.9 GHz image	eovsa_yyyymmdd.spw31-43.tb.disk.fits

Getting level 2 data

EOVSA Level 2 data products can be retrieved with the following steps:

• go to EOVSA browser page.

• Browse to the date of interest.
• Click "synoptic fits" button next to the calendar tool.
• Select the data product based on the names listed in the table above.

Reading level 2 data

Software

suncasa

All-day TP spectrum

Daily total power full-Sun-integrated spectrogram calibrated in solar flux units are provided at 451 frequencies (134 frequencies prior to 2019 Feb 22) and 1 s time resolution. To read a spectrogram file in Python using the suncasa library:

from suncasa.eovsa import eovsa_dspec as ds
## define the dynamic spectrum file.
tpfits = 'EOVSA_TPall_20190504.fts'
## display the dynamic spectrum. 
ds.dspec(tpfits,vmax=200)

The following code will read the spectrogram file in IDL:

function dspec,filename,doplot=doplot
  ; Read EOVSA Dynamic Spectrum FITS file <filename> and return a spectrogram object.
  ; Optionally show an overview plot if doplot switch is set
  ; 
  ; Usage:
  ;    s = dspec(<filename>)            ; Returns spectrogram object
  ;    s = dspec(<filename>,/doplot)    ; Plots spectrum and returns spectrogram object
  ;
  ; To access the data in the spectrogram object, use
  ;    spec = s.get(/spectrogram)    (Array of amplitudes in SFU, of size ntimes, nfreq)
  ;    fghz = s.get(/spectrum_axis)  (Array of frequencies in GHz, of size nfreq)
  ;    ut = s.set(/time_axis)        (Array of UT times in anytim format, of size ntimes)
  
  default,doplot,0
  spec = mrdfits(filename,0)
  freq = mrdfits(filename,1)
  time = mrdfits(filename,2)
  fghz = freq.sfreq
  ut = anytim(time)
  s = spectrogram(spec,ut,fghz)
  if doplot then begin
    window,/free,xsiz=1024,ysiz=600
    ; Find min and max of data from 5% to 95% of sorted array (eliminates outliers)
    sarr = sort(spec)
    dlim = minmax(spec[sarr[n_elements(sarr)*0.05:n_elements(sarr)*0.95]])
    ; Set drange with margin factor of 2 on low end and 5 on high end
    s.set,drange=dlim*[0.5,5]
    loadct,3
    s.plot,/log,/xsty,/ysty,ytitle='Frequency [GHz]',charsize=1.5
  endif
return,s
end

All-day XP spectrum

Daily cross power spectrogram (mean flux from baselines with "intermediate" lengths) calibrated in solar flux units are provided at 451 frequencies and 1 s time resolution. XP spectrogram has much better sensitivity to weak bursts.

from suncasa.eovsa import eovsa_dspec as ds
## define the dynamic spectrum file.
tpfits = 'EOVSA_XPall_20190504.fts'
## display the dynamic spectrum. 
ds.dspec(tpfits,vmax=30)

Synoptic 6-band Images

Full disk images at 6 selected frequency bands centered at 1.4, 3.0, 4.5, 6.8, 10.2, and 13.9 GHz are provided once per day, calibrated in brightness temperature.