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Analysis of a radio spectrum using SSWIDL

The two dimensional spectrum is of primary interest for analyzing a radio flare captured by a radio spectrometer like Callisto. It is used to analyze the flare structure as shown in figure 1. The spectrum allows us to define the type (I….IV) of the burst with its parameter like duration, bandwidth, drift rate and possibly intensity.

Figure 1 Top: Bright type II solar radio spectrum (raw data) of Bleien, Switzerland. This dynamic spectrum was taken using a biconical antenna connected to an up-converter in front of Callisto. Beside a pulsating carrier at 30 MHz the spectrum is mostly quite clean from interference. Figure 1 Bottom: Single frequency spectrum at a specific time. The second plot is a relative plot by subtracting a quiet spectrum 20 seconds earlier.

Double plot in figure 1 was created using SSWIDL, see also here: Many procedures of SSWIDL allow easy plotting of light curves, single spectra and two-dimensional spectra. It is even possible to ‘add’, ‘subtract’ spectra. In addition, it is also possible to append spectra in time-range or frequency range. But this will be shown in a later essay. The appended SSWIDL program plots on a graphic window of the monitor and prints a jpg file in the local directory. For publication it is often necessary to supply encapsulated post script files. In this case all semicolons in line 13-14 and 36-37 have to be taken away.

Attachment IDL program:

PRO PlotCallistoSingleSpectrum
; check path/file carefully


path = 'C:\Dokumente und Einstellungen\Christian\Eigene Dateien\Projects\Essays\Spectrum\'
file = ''

!p.multi = [0,1,2]; two plots in one column


radio_spectro_fits_read, path + file, z, x, y

zz = constbacksub( z, /auto ) & xx = x & yy = y

elimwrongchannels, zz, xx, yy

spectro_plot, zz, xx,yy , xs=3, ys=3,$
xrange = '2009-May-08 08:' + ['08:00','09:40'], yrange = [80,20],$
ytitle='Frequency [MHz]',$
title = 'Callisto low frequency observation Bleien, Switzerland',$

p0 = 488*4; reference spectrum? : (08:08:20 - 08:00:12) * number of sweeps per second
p1 = 508*4; spectrum of interest: (08:08:40 - 08:00:12) * number of sweeps per second
dy = z[p1,*] - z[p0,*]; subtract background
plot,y,dy, xtickinterval=10, yrange=[0,40],$
xtitle = 'Frequency [MHz]', ytitle = 'Relative intensity [ADU]',$
title = 'Single spectrum of 2009-May-08 at 08:08:40 UT',$


image3d = TVRD(TRUE=1)
WRITE_JPEG, path + 'MySpectrum.jpg', image3d, TRUE=1, QUALITY=100


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