**SOLAR\
RADIO**

**SPECTROGRAPH**

**\[ SRS \]**

**DATA VIEWER**

**\[ SRSDisplay \]**

*Viewer code by Graham Steward*

*Documentation by John Kennewell and Graham Steward*

*IPS Radio and Space Services*

*Learmonth Solar Observatory*

*PO Box 200*

*Exmouth WA 6707*

*AUSTRALIA*

**August 2003**

**CONTENTS:**

**1 Description of the SRS**

1.1 SRS History

1.2 SRS Equipment

1.3 SRS Data Archive

**2 Format of the SRS Archived Data**

2.1 SRS Data Files

2.2 SRS Data Records

**3 SRSDisplay - an SRS Data Viewer**

3.1 Overview

3.2 Running the Viewer

3.3 Operational Summary

**4 A Short Course in Data Interpretation**

4.1 Overview

4.2 Man-made Signals

4.3 Lightning, Short Wave Fades, and Meteor Echoes

4.4 Solar Signals

4.5 Summary

**1 Description of the SRS**

*1.1 SRS History*

The SRS or Solar Radio Spectrograph is a swept frequency radio telescope
for monitoring solar radio emissions originating mainly in the solar
corona. Its design was based on a solar radio spectrograph built by IPS
Radio and Space Services (Australia) at Culgoora (NSW). This instrument
was itself an upgrade to the original solar radio spectrograph designed
and built by the CSIRO. The first SRS prototype was designed and built
by IPS staff in conjunction with the RSTN (Radio Solar Telescope
Network) CRA (Central Repair Agency) at Palehua for the US Air Force
Space Command Solar ElectroOptical Network (SEON). The project was taken
over by SMC (Space and Missile Center - formerly SSSG) and contracted to
ARINC for production and deployment of 4 units to locations at Palehua
(Hawaii), Holloman (New Mexico), Learmonth (Australia) and San Vito
(Southern Italy). SRS units were deployed at these sites starting 1999.

*1.2 SRS Equipment*

The SRS covers a frequency range of 25 to 180 MHz, and completes a sweep
of this frequency range every 3 seconds. It does so using a two band
system. The low band (or A band) covers from 25 to 75 MHz. The antenna
used for this band is a non-tracking semi-bicone. The high band (or B
band) covers from 75 to 180 MHz. This uses a tracking log-periodic
antenna. Each antenna feeds its signal to a wideband preamplifier
(located at each antenna) and then via coaxial feedline to a HP8591E
spectrum analyser (one for each band). The two spectrum analysers and
then connected to a Data Acquisition computer (PC) using the GPIB
(IEEE-488) bus. This computer is networked to a Data Processing computer
where the signals are displayed to the operator. Further information on
the SRS may be found the Operations Manual for the Solar Radio
Spectrograph (SRS-OM-990801 / A/F 24U-10) prepared by ARINC.

*1.3 SRS Data Archive*

SRS data is archived monthly onto CD-ROM at each site and sent to NGDC
(WDC-A) in Boulder, Colorado, USA. A second copy is also sent to the
World Data Centre

for Solar Terrestrial Science at IPS Radio and Space Services in Sydney.

**2 Format of the SRS Archived Data**

*2.1 SRS Data Files*

To ensure that data is available for review and for later scientific
analysis, the SRS system archives the data it collects in two ways.

As data is collected in real time, it is written to a file called
SPEC.DAT which resides on the data processing (Unix) computer. At the
end of the day the contents of SPEC.DAT are written to an archive file
with the filename \"SSyymmdd.srs\" where SS is a two letter site
abbreviation. The four sites have the following abbreviations:

Learmonth LM

Palehua PA

Holloman HO

San Vito SV

At the end of each month, the previous month\'s files are written to a
CD-ROM. Note that because of the difference between local time and
Universal Time, some files from the adjacent months (ie at the start or
end of the month) may be included.

Apart from the site identifier, the filename contains the local date of
(most) of the data:

yy the last two digits of the year

mm the number of the month (01 to 12)

dd the day of the month (01 to 31)

Note that, again because of the difference between Universal and local
time, a local day file may contain data for two Universal Time days.

*2.2 SRS Data Records*

Each SRS day file consists of a number of binary records, each of length
826 bytes. A record contains all the data for a single sweep of the
frequency range from 25 to 180 MHz in two bands: 25 to 75 MHz (Band A)
and 75 to 180 MHz (Band B). There are no starting or terminating
characters separating individual records.

The 826 byte data record consists of a 24 byte header record followed by
two arrays of 401 data bytes each. The first 401 are the linearly spaced
data for the low band (A)

and are arranged in order of increasing frequency. The second 401 bytes
are similarly arranged data for the high band (B). Note that there are
401 bytes (rather than 400), because both the start and end frequencies
are present. Thus the first byte of A band is for a frequency of 25.00
MHz whereas the 401st byte is for 75.00 MHz. Each of these data bytes is
a binary number from 0 to 255 representing the output level of the each
spectrum analyser at that frequency. The scale employed here is
logarithmic.

The frequency of the n th data byte is given by the formulae:

f~A~ = 25 + 50 \* (n-1) / 400 MHz (for A band)

f~B~ = 75 + 105 \* (n-1) / 400 MHz (for B band)

The format of each record is as follows:

**Byte \# Description Format**

*General header information*

1 Year (last 2 digits) Byte integer (unsigned)

2 Month number (1 to 12) \"

3 Day (1 to 31) \"

4 Hour (0 to 23 UT) \"

5 Minute (0 to 59) \"

6 Second at start of scan (0 to 59) \"

7 Site Number (0 to 255) \"

8 Number of bands in the record (2) \"

*Band 1 (A-band) header information*

9,10 Start Frequency (MHz) Word integer (16 bits)

11,12 End Frequency (MHz) \"

13,14 Number of bytes in data record (401) \"

15 Analyser reference level Byte integer

16 Analyser attenuation (dB) \"

*Band 2 (B-band) header information*

17-24 As for band 1

*Spectrum Analyser data*

25-425 401 data bytes for band 1 (A-band)

426-826 401 data bytes for band 2 (B-band)

Site numbers (byte 7 of the general header information) are as follows:

Palehua 1

Holloman 2

Learmonth 3

San Vito 4

**3 SRSDisplay - an SRS Data Viewer**

*3.1 Overview*

SRSDisplay.exe is the executable code for an SRS data viewer. It should
run under Windows 95, 98, 2000 and possibly later versions of the
Microsoft Windows operating systems. The system requirements are
minimal, although processor speed will affect the refresh speed of the
data display. The program may be loaded into any directory/folder, but
it will look for SRS data files on a CD-ROM in drive D: by default.
Alternative drives may be selected.

The SRSDisplay viewer will allow the selection of any SRS data file in
the selected drive (and directory/folder if necessary). It will then
display the data records graphically in segments of about 30 minutes.
Several options exist to scan the entire

day file. An option also exists to measure the shock speed of type II
solar bursts.

A limited hard copy print facility is provided, but this will not work
with all printers.

An alternative printing method is described later in this section.

*3.2 Running the viewer*

The SRS viewer SRSDisplay.exe is activated in the normal manner (eg
double click on the filename). The PC display settings must be set to a
screen resolution of 800x600 or higher (otherwise not all the viewer
screen will be visible on the PC monitor).

The SRSDisplay window that first appears has a large central black area
(in which the data records will be displayed). Along the top of the
window are 6 buttons and two slider controls. The frequency axis
(ordinate) is labelled from 25 to 180 MHz in a logarithmic manner. The
time axis (abscissa) does not initially show any time marks.

On the right hand side of the window is a colour map showing the colours
that are associated with pixel intensities over the entire intensity
range. This colour intensity scale from 0 to 255 is a relative
logarithmic scale - because of many factors it is not possible to
provide an absolute calibration of solar radio signals over this
frequency range in SFU (Solar Flux Units).

To display SRS data, the relevant SRS data file must be selected. This
is done by clicking on the \<Select\> button at the top left hand corner
of the viewer window. The default drive is the D: drive but this may be
changed to select whatever drive and directory/folder contains SRS data
files. If the default or chosen directory contains SRS data files (with
.srs extension) there will be displayed in the pop-up window.

Double clicking on any SRS file will launch the viewer to open that
file. Alternatively the filename may be typed in the appropriate window
and the \<Open\> button clicked. If no SRS file names appear in the Open
window, it is possible that a CD-ROM containing SRS files has not been
loaded into the CD-ROM drive.

When an SRS file has been selected and opened, the pop-up selection
window will disappear, and the viewer should then display the first 30
minutes of data of the chosen file. Time marks and labels will now
appear along the time axis. A mouse click anywhere in the data display
window will indicate the frequency, intensity and time of the pixel at
the tip of the cursor arrow. This data is written on the screen just
above the top left hand corner of the data display window. Frequency is
in megahertz, intensity is in relative logarithmic units (0 to 255) and
the time is Universal Time.

To obtain an overview of the data in the selected file, the \<Browse\>
button may be clicked. This will always start at the beginning of the
data file and show successive 30 minute segments of data until the end
of the file is reached. There is an approximate 2 second delay between
successive displays. However, if a slower computer takes more than 2
seconds to paint the screen with data, there will appear to be no delay
between successive segments. The \<Stop\> button may be used at any time
to interrupt this scan or browse function to enable an interesting
segment to be perused in more detail.

An alternative way to select a data segment for viewing is to use the
lower (and longer) slider control just above the top right hand side of
the data display. At the left hand side of this slider are the date and
time of the first record of the data file, while on the right hand side
are the date and time of the last record of the data file. Above the
slider is the time (View Time) of the first data record currently being
display in the data window below. By dragging the slider along with the
mouse (position the mouse on the slider, hold down the left button, drag
the slider along, then release the button) you can have the viewer draw
a 30 minute data segment starting at any time within the data file.

The \<Print\> will produce a hard copy of the displayed spectrum on a
printer attached to the PC. Unfortunately not all printers will produce
an acceptable image using this button. Most deskjet printers appear to
be OK, but laser printers may be problematic.

An alternative way to print the SRS display window is to hold done the
\<ALT\> key and press the \<Print Screen\> key on the keyboard. This
will capture the SRSDisplay window to the clipboard. From here the image
may be \'pasted\' into a graphics program such as Microsoft Paint and
printed from there.

The \<Shock Speed\> button may be used to compute the speed of the wave
producing a type II solar burst. When a type II burst is displayed in
the window, press the \<Shock Speed\> button. A pop-up window entitled
\"Calculate Shock Speed\" will appear. Next select whether the
fundamental or harmonic emission is to be measured. In some cases, when
only one emission band appears, it may be difficult to decide whether it
is fundamental or second harmonic. In general fundamental emission will
lie in the lower frequency range (25 to 60 MHz) whereas second harmonic
emission will encompass 50 to 120 MHz. However, on occasion, type II
emission may lie outside these stated limits.

After the emission mode has been selected, the mouse is moved along the
lower edge of the burst and frequency-time data pairs are acquired by
clicking the left button of the mouse at points along this edge. At
least four points (but no more than 20) should be entered, and these
should be spaced along the whole of the edge for best shock speed
estimation. When these points have been entered (no visible display is
given to acknowledge the clicks), the \<Calculate\> button should be
clicked (or the \<Abort\> button if it has been decided not to continue
with the calculation), A new pop-up window will replace the former one.
This is titled \'Shock Speed and Regression Fit Correlation\'. In this
window will be displayed the computed shock speed, the regression
correlation coefficient of the least squares fit to the points entered,
and the extrapolated time of the event at the photosphere. Note, this
does not mean that the event actually started at the photosphere. It is
simply the time the event would have been at the photosphere assuming a
constant velocity projected backwards in time.

The model of coronal electron density used for the shock speed
calculations is the original model of Gordon Newkirk, referred to as
Newkirk x 1. The reference is

Astrophysical Letters, 1975, vol 16, pp23-28, equation 10.

The pop-up window also contains a graph of modelled shock height versus
time.

The height is given as R/Rs, the fractional solar radius, with the
photosphere having a value of 1.0. The time axis is plotted in seconds
from the first data point. The data points are indicated as white dots,
and the modelled shock speed is indicated as a solid line. The pop-up
window can be dismissed by clicking on the \"X\" in the upper right
corner.

In the main window the \<Quit\> button will exit the program. The slider
in the top right of the window labelled \"Threshold\" may be used to
black out any part of the display below (less then) the selected
intensity level. The default threshold is 0, and it may be set as high
as 250. Every time this slider is moved, the display will be repainted
using this threshold with the current 30 minute segment of data.

*3.3 Operational Summary*

\* The SRSDisplay viewer may be run from any directory/folder under
Microsoft

operating systems Win 95, 98 +.

\* By default the program expects SRS data files with an \"srs\"
extension in the D:

drive (CD-ROM). Alternative data locations may be selected

\* The \<Select\> button allows a specific SRS data day file to be
chosen.

\* The \<Browse\> button automatically scans through and displays 30
minute segments

of the entire selected file. This process may be halted at any time with
the

\<Stop\> button.

\* The \<Print\> button allows a hard copy of the display to be sent to
many deskjet

printers. It will not work with all printers. An alternative print
method has

been described above.

\* The \<Shock Speed\> button brings up a pop-up window with
instructions on how to

measure the shock speed of a type II solar radio burst.

\* The \<Quit\> button exits the viewer program.

\* The \'View Time\' slider allows rapid selection of any 30 minute
segment of data

within the file start and end times (which are displayed at each end of
this

slider).

\* The \'Threshold\" slider allows plotting of pixels only above the
chosen intensity.

\* Intensity is colour coded (0 to 255) according to the bar shown to
the right of the

display.

\* Clicking on the spectral display with the left mouse button will
indicate the exact

frequency, time and intensity (top left of display).

**4 A Short Course in Data Interpretation**

*4.1 Overview*

The frequency range of solar coronal emissions (and hence the frequency
range employed by the SRS) lies in the high HF and the VHF spectrum,
which is used widely by human society for communications and other
purpose. Consequently a large number of man-made transmissions occur in
this band. As a result, it is necessary for a solar radio astronomer to
be able to distinguish not only one type of solar radio emission from
another, but also solar radio emissions from man-made and some natural
terrestrial emissions.

As a very general rule, man-made transmissions appear as a vertically
narrow horizontal lines on the SRS display, whereas solar emissions
appear as vertical structures.

*4.2 Man-made Signals*

The man-made emissions that may appear on the SRS are HF communications
(from 25 to 30 and sometimes to 50 MHz). These transmissions may be from
local (nearby) transmitters, but most of them will be received from
large distances via ionospheric propagation. This type of interference
will vary during the day, being weaker in the morning hours and most
intense around midday to mid-afternoon, when the ionosphere overhead has
it greatest density. There is also a strong correlation with solar
cycle. During solar minimum (thin ionosphere), little HF interference
will be noted, whereas at solar maximum (dense ionosphere), HF
interference may cover the entire lower portion of the SRS display.

TV transmitters (which usually operate 24 hours a day) may occupy
frequencies from 45 to 88 MHz and from 170 to 180 MHz. FM broadcasting
stations, which also operate continuously in many parts of the world,
occupy the frequency range 88 to 108 MHz. At some SRS sites,
interference from TV and FM transmitters is so strong that it has been
necessary to place blocking filters over a range of frequencies to
prevent SRS receiver overload. In this case, one sees, a bite-out of the
RF spectrum, indicated by a horizontal band of reduced intensity. Both
FM and TV transmitters produce continuous horizontal lines across their
display. A TV transmitter produces three horizontal lines, one for the
main video carrier, one for the colour subcarrier and one for the audio
subcarrier. In the US, the colour subcarrier is spaced 3.58 MHz above
the video carrier, and the audio carrier is 4.5 MHz above the video
carrier. In Australia, the separations are 4.43 and 5.5 MHz
respectively. In Europe, the spacings may be different again, depending
on whether the TV station is in France, Italy or Germany.

The frequency range from 108 to 136 MHz is used by commercial aviation.
IN the lower part of this band are navigational beacons (108 to 118 MHz
as a rule). These result in continuous horizontal lines across the
display (as for FM transmitters, although they are much lower power).
Air to ground and air to air communications result in interrupted or
staccato horizontal lines across the display. Similar broken lines can
result from marine communications in the 156 to 158 MHz segment.

Satellites carrying beacons are found in the 136 to 138 MHz. These will
produce horizontal lines that fade in and out as the satellite crosses
the horizon in less than about 30 minutes. Only low Earth orbiting
satellites (LEO) are close enough to produce a trace on the SRS
displays. The strongest satellite signals are from the constellation of
ORBCOMM communication satellites.

Various public utilities (water, electricity, rail, police, ambulance,
emergency services, pagers) use frequencies from 60 to 88 MHz and 150 to
180 MHz. Military communications may occur in the 30 to 80 MHz band.
These are all generally broken horizontal lines. Allocated frequencies
will vary from country to country, and reference to the appropriate
authorities\' publications can help resolve queries as to the source of
various man-made transmission. The FCC (Federal Communications
Commission) is the approving authority in the USA, whilst the ACA
(Australian Communications Authority) is the relevant agency in
Australia.

Local interference, from machinery, can be broadband in appearance and
have a vertical structure that may be similar to solar radio bursts. It
can generally be distinguished from the latter in that it has sharp
leading and trailing edges (ie switch transitions).

And finally, in the sphere of manmade transmissions, some SRS sites are
co-located

with ionospheric radars (ionosondes) which scan the frequency range from
about 1 to 20 MHz twice an hour (other nearby ionosondes may sound even
more frequently). Although this frequency is not within the range of the
SRS, the harmonics of the ionosonde transmitter may be seen in the lower
frequencies. It will consist of closely spaced lines sloping from lower
left to upper right, and will repeat at regular intervals.

*4.3 Lightning, Short Wave Fades, and Meteor Echoes*

Lightning discharges from electrical storms create signals over a wide
spectral range, and may be seen at the lower frequencies in an SRS
display. Occurrence is normally in the local summer. The signature is a
series of short erratic vertical lines with random spacing, and varying
intensity over the line.

A phenomena which results in not an increase in intensity but a decrease
may be caused by a solar X-ray flare. This results in a short wave
fadeout where the ionospherically propagated HF interference is seen to
be reduced in intensity for a time of a few minutes to hours.

Distant transmitters (eg FM stations) may occasionally reflect off the
ionised trail left when a meteoroid enters the Earth\'s atmosphere.
These will appear as bright points,

or in the case of reflection from multiple closely spaced transmitters,
groups of points.

*4.4 Solar Signals*

Solar radio emission are generally classified into one of six different
types.

Type I Solar noise storm - narrow band spikes (many vertical lines, each
of

which is limited in vertical (frequency) height, although wider than

man-made transmissions, and narrow in time (a few seconds).

Type II A slow drift burst which slopes from top left to bottom right.
Normally visible with both a fundamental and second harmonic band.

Type III A \'fast drift\' burst. One or more vertical patches of
emission over a

wide frequency range and a few seconds duration. Many individual

burst normally occur together to produce a much wider structure in

time.

Type IV Continuum emission with a wide frequency bandwidth, and lasting
for many minutes to hours. Normally only occurs in

conjunction with a large solar eruptive event.

Type V Only associated with and following type III emission, short
duration continuum at the lower frequencies attached to the type III
emission.

Unspecified Continuum. Wide frequency range and long lasting - may have

superimposed type III and type I emission.

Type I emission is usually cyclotron emission coming from electrons
spiralling around the magnetic field lines near an active region of the
Sun.

Type II is a plasma emission coming from different heights in the corona
as a shockwave (due to the passage of supersonic plasma) propagates
outward from the source.

Type III is also a plasma emission but the exciting cause is believed to
be a relativistic electron stream.

Type IV emission is synchrotron emission from relativistic electrons
ejected high into the solar corona. Type IV emission has been subdivided
into many categories by different authors.

Type V is a ringing of the plasma that occurs following the stimulation
of a type III shock.

Any other continuum may be synchrotron emission associated with high
speed electrons circling various magnetic structures, or it may be dense
type I or type III activity or a mixture of all three giving the
impression of a continuous wideband emission.

*4.5 Summary*

The SRS display will contain radio emissions from man-made and solar
sources, and other natural sources of radio signals. One very rough rule
of thumb is that man-made signals will appear as narrow horizontal
lines, either continuous or broken, whereas solar signals appear as
wider vertical or sloping structures. However, there are exceptions to
this rule, and only by experience and a knowledge of both solar radio
emissions, and the local radio environment will it be possible to
identify most traces.

It is worthwhile to point out that the SRS displays are useful not only
in the study of solar radio bursts, but may be also used in studies of
ionospheric radio propagation and other fields.

A powerpoint presentation showing graphic examples of typical SRS
signals is available. **\[SRSData.ppt\]**

**