The Swedish Ionosondes.
Lecture notes 12.08.2005
http://www.irf.se/~ionogram
Christer Juren (IRF)
Ionogram data from Kiruna, Lycksele and Uppsala, 1976 - 1989
One transmitter pulse and its return from the Ionosphere as two pulses!
Keywords: Ionosphere, Magnetosphere, Radio waves(short waves), Ionograms,
Computer Graphics, Objectoriented programming, parallel programming, Interactive
whatever.
The Ionosphere.
They found when transmitting radio waves at the beginning of the 20th Century that
the waves could reach far behind the horizon. From their knowledge of how waves in
general propagate, several people suggested diffraction – that waves may bend
around corners. After lot of thinking one understood that was not the case. O.
Heaviside and others suggested instead that up in the sky there was an electrical layer
like a conducting plate, which simply reflected the waves. Electrical currents, which
were equal to a conductivity times the electric field in the wave, generated the
reflection. Later it was understood that this was not the case either for high frequency
waves (some MHz. “ordinary short waves”) but it could explain the reflections for
low frequency waves.
With some experiments one found that free electrons at heights between 100 km and
600 km could reflect waves with a frequency equal the electrons plasma frequency at
the place where the reflection occurred. The plasma frequency is proportional to the
square root of the free electron density, and 400 kilometres up in the sky it is around 5
MHz.
One found two types of reflected waves different in polarization, O- and XO-modes.
The famous physicist Lorentz had a theory about radio waves propagating along a
magnetic field where free electrons existed. He discussed two wave modes, but it was
only one of these two that was detected from the ionosphere, but together with a third
one.
Lorentz’s second wave mode was detected when one started to use ionosondes up in
the north in Kiruna during the 1940th. It is about a singularity and to appear it has to
be a very special situation. Where the plasma frequency is equal to the wave
frequency the wave has to go strictly along the magnetic field. In north the magnetic
field has an almost vertical direction so for an almost vertical propagation it can
happen.
Today we talk about three types of reflections from the ionosphere, O, XO and Z. I
connect the O-mode to the mode Lorentz missed and the other two to the Lorentz
modes! One should be careful about nomenclatures and always try to get one’s view,
which one can explain.
The name “Ionosphere” appeared first officially in 1926 in an article by Gardiner as
an analogy to “stratosphere” and ”troposphere”, but had been suggested by Appleton
in a letter to Ratcliff 6 days before. The term Ionosphere started to be generally
accepted and used first in the beginning of the 1930s.
The Ionograms.
An ionogram from Lycksele recorded during 1984. The three main parameters are
shown. A summer ionogram
An ionogram from lycksele recorded with transpusonde during 2003. A winter
ionogram. The white curve is the plasma frequency related to height.
The same transmitting as above in Lycksele but the ionogram has been recorded
in Kiruna. A typical nose appears to the right.
Illustration of the two modes described by Lorentz.
One ionogram:1958 march 22 08 09 from 16mm film
to the left (512*390) pixels (8 bits),
in the middle (256*145) pixels (8 bits) and
2% simple wavelet compression to the right. The wavelet coefficients to lower
right.
The necessary number of bits per pixel can be changed to 7.11 less than 8.
Transpusonde at IRF (Swedish Ionosondes)
Data to the database NGDC from Kiruna, the day 1995-07-14.
1116795071442025 022 014 011 010EE010EE010EE010 010 010 011 011
1116795071434 B B125 120 G G G100 115 115 105 105
1116795071430025EB022EB019 021 023EG026EG028EG029EG057 039 053 052
1116795071436
L CL
CL C CL CL
1116795071432025EB022EB018 021 023EG026EG028EG029EG030 G033 036 037
1116795071424 B B B A100 100 100 100 100 105 100 100
1116795071420 B B A A230 260 H280 H285 300 305 305DA285DA
1116795071426
1116795071422
1116795071416265EB275EB250 240 225 230 215 215 215 245 A A
1116795071410
L L350 350 380 395 405 410 425 425
1116795071404
L L350 360 340 430 410 405 345 405
1116795071452
1116795071402
1116795071400044DR036 039 039 043 045 046 045 048 048 050 050
1116795071451 R043 X046 X046 X050 X052 X053 X052 X055 X055 X057 X057 X
1116795071403 R310 315 320 310 315 325 270 290 290 315 285
1216795071442013 010 010 014 012 024 022 016ES018 020 025 018
1216795071434095 095 105 G G145 125 135 135 105 130 130
1216795071430056 053 032 027EG027EG031 034 032 035 056 056 032
1216795071436L L L
H C R R RL RR R
1216795071432037 035 031 027EG027EG025 G031 023 027 056AA056AA032AA
1216795071424100 A100 100 110 B A A B B B B
1216795071420270DA A230DA265 265 255 A A B B B B
1216795071426
1216795071422
1216795071416 A A215 H215 200 H240 A A310 A A A
1216795071410425 420 410 405 385 360 355 315
1216795071404370 375 405 390 350 335 325 340
1216795071452
1216795071402
1216795071400048 048 047 045 047 043 044 043 042 A A A
1216795071451055 X055 X054 X052 X054 X050 X051 X050 X049 X A A A
1216795071403300 305 295 300 320 310 315 310 315 A A A
http://www.iono.noa.gr/DIAS
Dynagram and Dynasonde
Dynagram with direction
Dynagram together with the directions for the received pulses in stereo
Dynasonde in Lycksele, two receivers and one transmittercontroller.
Crossed dipoles for detection of wave polarization.