UNIVERSITY OF CRETE
PHYSICS DEPARTMENT
Laboratory of Atmospheric and Ionospheric Physics
Attn. C. Haldoupis,
Physics Department, University of Crete,
Iraklion 710 03, Crete, Greece
tlf +30-81-394222, +30-81-394242, Fax : +30-81-394201
e-mail : chald@physics.uoc.gr
Iraklion, January 2000
SESCAT : A PROJECT for MIDLATITUDE IONOSPHERIC E REGION
BACKSCATTER STUDIES
SESCAT is an ionospheric plasma physics collaborative research project between the
Univeristy of Crete, Greece (Dr. C. Haldoupis) and Max-Planck Institut fuer Aeronomie, Germany (Dr. K. Schlegel). Its aim is the experimental and theoretical study of
very high frequency (VHF) radio wave coherent scattering phenomena which are known to occur in the midlatitude E region ionosphere. SESCAT, which
stands for Sporadic E SCATter experiment, refers to a continuous wave (CW) radar facility which has been operating in Crete since 1992. The
experiment is a state of the art bistatic CW Doppler radar operating at 50.52 MHz with the transmitting and receiving arrays beaming northward to a
region perpendicular to the earth's magnetic field at the E region peak. As shown in the following figure, the viewing area in SESCAT, determined by
the narrow beam intersecting patterns and the field-aligned, i.e., magnetic aspect sensitive, character of the scattering plasma irregularities, is
fixed at about 15 x 40 km2 and located over the southern Aegean at 30.8 degrees invariant magnetic latitude (L =
1.35).
Map showing the experimental configuration and SESCAT geometry with geographic and geomagnetic information.
The system can observe coherent backscatter from plasma waves propagating
perpendicular to the earth's magnetic field and along the bisector formed by the incident and received radio wave. The thick line across
the viewing area represents the locus of perpendicularity between the observing direction (i.e., the bisector of the angle between Tx-scatter region-Rx) and
the magnetic field. The transmiter and receiver sites are located in the northern coastline of Crete near the
city of Iraklion and Chanea, respectively. In each site The antenna systems are identical arrays, each consisting of four high-gain Yagis all
tuned at 50.5 MHz (lambda = 5.98 m). Each yagi is based on proven design rules having 11 elements, that is a folded dipole, reflector, and nine directors;
distributed along a boom of 2.5 lambdas (about 15 m) and resulting in a 12-dB gain; a 3-dB beamwidth of 35 degrees and a first sidelobe suppression
of -18 dB. The 4 Yagis were placed 8 m (1.35 lambda) apart to form a four-antenna array for each site with an overall gain of 18 dB and a +-
3-dB beamwidth of 8 degrees in the azimuthal plane. All antennas have their radiating dipole placed at about half wavelength above ground (about 3 m) and
are tilted upward at 30 degrees relative to the horizontal in order to deliver their radiation maximum perpendicular to B near 110-110 km altitudes
in the E region of the ionosphere. Since 1993, SESCAT operates automatically, using digital signal processor (DSP) technology for real time fast Fourier
transform processing, and is capable of recording high resolution Doppler spectra on a continuous basis and at a minimal operational cost. For more
information on SESCAT see Haldoupis and Schlegel, Radio Science, Vol. 28, p 959, 1993.
The receiver SESCAT site in Akrotiri, Chanea, Crete
From radar and rocket observations it is well known that meter-scale
electron density inhomogeneities (plasma waves) do exist in the E region of the ionosphere in the altitude range from approximately 95 to 120 km with
maxima near 105 km. The basic underlying physical reason for these phenomena is the unique plasma properties at these ionospheric heights imposing
a different behavior for the opposite charge particles, that is the massive ions become unmagnetized because their motion is controlled by
collisions with neutrals, whereas the electrons become strongly magnetized because their gyrofrequency is much greater than the electron-neutral collision
frequency. This inherent E region plasma property leads to differential electron-ion motions in the presence of an ambient electric field and,
consequently, to the flow of electric currents. These currents alone, or in conjunction with electron density gradients, are believed to be the primary source of
energy that sustains, through plasma instability mechanisms and nonlinear interactions, the short-scale electrostatic
irregularities at these E region altitudes which propagate perpendicular to the magnetic field and can cause strong coherent backscatter of the
incident VHF radio waves. The most pronounced E-region coherent scatter phenomena occur in the magnetic equatorial
and high latitude (auroral) zones where favourable field geometries and relatively large electric fields combine in generating ExB currents known
as the equatorial and auroral electrojets. On the other hand, there is also lower- and mid-latitude E-region backscatter occurrence
from meter scale field-aligned irregularities, which, till recently, has received much less attention. The existing evidence suggests that this
scatter relates often to the commonly observed mid-latitude sporadic E layers, Es, which
are accompanied by sharp electron density gradients and large metallic ion concentrations.
It is believed that during Es conditions and local E-field intensifications a plasma
instability generates the field-aligned irregularities which strongly scatter HF and VHF
radio waves.
SESCAT was conceived and implemented in order to increase our understanding of
midlatitutde E region plasma physics. Its successful operation the last few years proved that Crete is an excellent location for the observation of midlatitude 50
MHz backscatter. Several interesting results were obtained and more are expected to come from the continuation of
research. For more information on the
SESCAT scientific output and resulst see below the list of listed references. Here, in this WWW page, we would like to refer and
emphasize only an important SESCAT observation, namely the detection for first time of
Type 1 plasma waves in the midlatitude E region ionosphere. Type 1 irregularities, which
occur regularly in the equatorial and auroral electrojets because electric fields there take up relatively large values, are generated
by the modified two stream, or Farley-Buneman, plasma instability. The observation for first time of Type 1 plasma waves at midlatitudes implied the
existence at times there of large electric fields, at least as large as 15 mV/m, i.e., an order of magnitude higher than the averaged ambient
ionospheric field. This is an important result for ionospheric science that needs to be investigated and understood. A typical midlatitude Farley-Buneman
event, as seen by SESCAT, is shown in the following figure.
The lower coloured plate shows a Doppler spectrogram during a period of
type 1 scatter occurrence. The upper pannel shows the mean and peak Doppler velocity changes with time. There are at least three cases of dominant type 1 plasma waves
seen in this period with phase velocities near 360 m/s that imply electrc fields as high as 16 mV/m
SESCAT was expanded recently into a dual receiver CW Doppler radar interferometer and the
first interferometric observations were recorded during two separate data collection
campaigns in the summer of 1998 and presently we are in the process of analysis and
interpretation. An example of interferometer recordings are shown in the following Figure:
At present, our aim is to keep SESCAT's operation going for the next few years and try a
number of new experiments in order to gain additional insight into the physics of the midtlatitude coherent backscatter phenomena.Among our
imminent research plans is the performance of joint experiements with additional instrumentation in collaboration with interested groups from Germany,
Canada, and the United States, the expansion of the receiver system into both, horizontal
and vertival radio interferometer, the interpretation of results, and the development of
theory.
Acknowledgements
Volkswagen Stiftung provided a grant (I/65808) that made this experiment possible.
Additional monetary support was made available by the Max-Planck Institut fuer Aeronomie and the University of Crete. Thanks go
also to several individuals for their help; these include V. Thiel and W. Butchek of
Max-Planck Institut fuer Aeronomie (for their help in the installation of antennas in
Crete), Tasos Kampurelis for his excellent work on developing software for SESCAT data
analysis, Vasilios Virvilis for real time DSP software processing, Dimitrios Zouridis for
continuous technical support, Christos Ragiadakos, Toula Grispolakis and George Siganakis.
The valuable cooperation of the Technical College of Iraklion (TEI) and the Polytechnic
University of Chanea, Crete for allowing the use of their land for the SESCAT sites, is
also acknowledged. SESCAT is run jointly by the University of Crete and the
Max-Planck-Institut fuer Aeronomie.
DATA AVAILABILITY NOTE: In principle, SESCAT data can be made available to any scientist
in the world who maintains a research interest on the subject. If interested please contact: C. Haldoupis (chald@talos.cc.uoc.gr) or K. Schlegel (schlegel@linmpi.mpg.de).
SESCAT: Scientific output: PUBLICATIONS and
PRESENTATIONS
1) A Bistatic 50 MHz radio system for coherent backscatter studies of mid-latitude
sporadic Es layers: A proposal, C. Haldoupis and K. Schlegel, Max-Planck Institut fuer Aeronomie, Research report, MPAE-W-05-91, 17, Aug. 1989
2) SESCAT - A new 50 MHz Radio Doppler System for Coherent Backscatter Studies of
Mid-Latitude Sporadic E-Layers, K. Schlegel and C. Haldoupis, Extended Abstract, Paper presented at the Workshop on Coupling, Energetics and Dynamics of
Atmospheric Regions, Boulder, Colorado, June 18-20, 1992.
3) Ionospheric E Region Plasma Instabilities: A review of the linearized theory and
derivation of the general dispersion relation, N. Christakis, student thesis, Physics Department, University of Crete, Iraklion, March, 1992.
4) A new radio Doppler experiment for mid-latitude E-region coherent backscatter studies,
C. Haldoupis and K. Schlegel, 1st Panhellenic Astronomical Conference, Athens, Sept 21-24, 1992 (in Conference
Proceedings, p. 346-352, 1993)
5) Ein neues 50 MHz Doppler radar zur Untersuchung Kohaerenter Rueckstreuung in
Sporadischen E-Schchten Mittlerer Breiten, K. Schlegel and C. Haldoupis, FRG, 1992.
6) A 50 MHz radio Doppler experiment for mid-latitude E-region coherent backscatter
studies. System description and first results, C. Haldoupis and K. Schlegel, Radio Sci., 28, 959-978, 1993.
7) Scattering phenomena of radio waves from plasma irregularities in the E-region of the
earth's ionosphere, (invited paper) C. Haldoupis, 2nd Panhellenic Conference on Solar and Space Physics, Xanthi, April 26-29,
1993 (in Conference Proceedings, p. 216-240, 1994).
8) Observations of coherent backscatter from mid latitude sporadic E layers with a new
coherent 50 MHz radar, K. Schlegel and C. Haldoupis, XVIII General Assembly, European Geophysical Society, Wiesbaden, Germany,
May 3-7, 1993.
9) 50 MHz observations of mid-latitude ionospheric E-region coherent backscatter, K.
Schlegel and C. Haldoupis, XXIV General Assembly of the International Union of Radio Science,Kyoto, Japan, Aug. 25 -
Sept. 2, 1993.
10) Observation of the modified two-stream plasma instability in the midlatitude E region
ionosphere, K. Schlegel and C. Haldoupis, J. Geophys. Res., 99, 6219-6226, 1994.
11) Evidence of Farley-Buneman plasma instability occuring at midlatitudes, K. Schlegel
and C. Haldoupis, IXX General Assembly, European Geophysical Society, Grenoble, France, April 25-29, 1994.
12) Electrical currents and Farley-Buneman turbulence in midlatitude sporadic E-layers, V.
A, Liperovsky, C.-V. Meister, C. Haldoupis, and K. Schlegel, XIX General Assembly, European Geophysical
Society, Grenoble, France, May, 1994.
13) Application of a Digital Signal Processor (DSP) in a PC based system for automatic
Doppler spectrum recordings of an ionospheric scatter radar experiment, V. Virvilis, Student Thesis, Physics Department, Universisty of Crete,
Iraklion, October 1994.
14) Characteristics of midlatitude E region coherent backscatter obtained with SESCAT, C.
Haldoupis and K. Schlegel, XX General Assembly, Hamburg, 3-7 April, 1995.
15) New results from midlatitude E-region coherent backscatter observed with SESCAT, K.
Schlegel and C. Haldoupis, Workshop on E-region plasma instabilities, MPAE-EGS, Lindau, Germany 24-27 October, 1995.
16) On midlatitude ionosphere E region type 1 echoes. Observational characteristics and a
possible interpretation, C. Haldoupis, K. Schlegel, D. T. Farley, Workshop on E-region plasma instabilities, MPAE-EGS, Lindau, Germany
24-27 October, 1995.
17) Coherent backscatter from the E-region/mesosphere over Crete, Greece. K. Schlegel and
C. Haldoupis, 7th Workshop on Technical and Scientific Aspects of MST/ST radar, South Carolina, USA, Nov. 7-11, 1995.
18) SESCAT: A 50-MHz radio Doppler experiment for midlatitude E-region Coherent
backscatter studies, K. Schlegel and C. Haldoupis, 7th Workshop on Technical and Scientific Aspects of MST/ST radar, South Carolina, USA, Nov. 7-11, 1995.
19) An explanation for type 1 radar echoes from the midlatitude E region ionosphere, C.
Haldoupis, K. Schlegel, and D. T. Farley, Geophys. Res. Lett., 23, 97-100, 1996.
20) Characteristics of midlatitude coherent backscatter from the ionospheric E region
obtained with SESCAT, C. Haldoupis, and K. Schlegel, J. Geophys. Res., 101, 13,3387-13,397, 1996.
21) Observations of coherent scattering at 50 MHz from electrostatic plasma waves in the E
region of the midlatitude ionosphere, C. Haldoupis and K. Schlegel, 6th National meeting of the Union of Greek Physicists, Iraklion, Crete, April 4-7, 1996.
22) New results from mid latitude E-region coherent backscatter observed with SESCAT, K.
Schlegel and C. Haldoupis, Proceedings of Workshop on E-region plasma instabilities, Cuvillier Verlag, p 27-30,
Goettingen, Germany, 1996.
23) On midlatitude ionosphere E region type 1 echoes. Observational characteristics and a
possible interpretation, C. Haldoupis, K. Schlegel, D. T. Farley, Proceedings of Workshop on E-region plasma instabilities, Cuvillier Verlag,
p 39-42, Goettingen, Germany, 1996.
24) Currents and turbulence in and near mid-latitude sporadic E layers caused by strong
acoustic impulses, V. A. Liperovsky, C.-V. Meister, K. Schlegel, and C. Haldoupis, Ann.
Geophysicae, 767-773, 1997.
25) Type 1 radar echoes from the midlatitude E region, C. Haldoupis,D.T. Farley, and K.
Schlegel, Ann. Geophysicae, 908-917, 1997.
26) Simultaneous observations of E region coherent radar echoes at 2m and 6m radio
wavelengths at midlatitude, J. A. Koehler, C. Haldoupis, K. Schlegel, and V. Virvilis, J.
Geophys. Res, 17,255-17,265, 1997.
27) Simultaneous coherent backscatter and digisonde observations in the midlatitude E
region, G. Hussey, K. Schlegel, and C. Haldoupis, European Geophysical Society annual meeting, Vienna, Austria, April 21-26, 1997.
28)Mid-latitude E region coherent backscatter and digital ionosonde simultaneous
observations, G. Hussey, K. Schlegel and C. Haldoupis, Canadian Association of Physicists, University of Calgary, Calgary, Alberta, June 8-11,
1997.
29) A review on radio studies of midlatitude E region ionospheric irregularities,
(invited), C. Haldoupis, 8th Scientific Assembly of IAGA (International Association of Geomagnetism and Aeronomy), Uppsala, Sweeden, Aug 5 to
Aug 13, 1998.
30) Simultaneous observations of midlatitude E region coherent radar echoes at 50
MHz and 144 MHz, J. A. Koehler, C. Haldoupis, and K. Schlegel, 8th Scientific Assembly of
IAGA (International Association of Geomagnetism and Aeronomy), Uppsala, Sweeden, Aug 5 to
Aug 13, 1998.
31) Simulteneous 50 MHz coherent backscatter and digital ionosonde obsrvations in the
midlatitude E region, G. C. Hussey, K. Schlegel, and C. Haldoupis, J. Geophys. Res., 103,
6991-7001, 1998.
32) Large polarization electric fields associated with midlatitude sporadic E, S.
Shalimov, C. Haldoupis and K. Schlegel, J. Geophys. Res., 103, 11,617-11,625, 1998.
33) Coherent backscatter studies of ionospheric irregularities associated with sporadic E,
(invited), C. Haldoupis, Western Pacific Geophysics Meeting, July 21-24, Taipei, Taiwan,
1998.
34) Farley-Buneman plasma waves in the midlatitude E region ionosphere, C. Haldoupis, K.
Schlegel, D. T. Farley, J. A. Koehler, and S. Shalimov, Western Pacific Geophysics
Meeting, July 21-24, Taipei, Taiwan, 1998.
35) Coherent backscatter cross section ratio measurements in the midlatitude E region
ionosphere, J. A. Koehler, C. Haldoupis, and K. Schlegel, J. Geophys. Res., 104,
4351-4359, 1999.
36) Evidence for planetary wave effects on midlatitude backscatter and sporadic E layer occurrence, M. Voiculescu, C.
Haldoupis, and K. Schlegel, Geophys. Res.
Lett., Vol 26, No 8, 1105-1109, 1999.
37) Midlatitude E region plasma accumulation driven by planetary wave horizontal wind shears, S. Shalimov, C. Haldoupis, M. Voiculescu, and K. Schegel, J.
Geophys. Res.,104, 28,207, 1999.
38) Large polarization electric fields associated with midlatitude sporadic E, S.
Shalimov, C. Haldoupis, and K. Schlegel, 9th Scientific Assembly, International Union of
Geomagnetism and Aeronomy (IAGA), Birmingham, UK, July 19-30, 1999.
39) First 50 MHz continuous wave interferometry measurements of licalized backscatter
regions in the midlatitude E region ionosphere, C. Haldoupis, A. kamburelis, K. Schlegel,
and M. Voiculescu, 9th Scientific Assembly, International Union of Geomagnetism and
Aeronomy (IAGA), Birmingham, UK, July 19-30, 1999.
40) Evidence for planetary wave effects on midlatitude backscatter and sporadic E layer
occurrence, M. Voiculescu, C. Haldoupis and K. Schlegel, 9th Scientific Assembly,
International Union of Geomagnetism and Aeronomy (IAGA), Birmingham, UK, July 19-30, 1999.
41) Dual radar frequency (50 and 144 MHz) coheren backscatter observations from 3-meter
and 1-meter irregularities in the midlatitude E region ionosphere, C. Haldoupis, J. A.
Koehler, K. Schegel and G. C. Hussey, XXVI General Assembly, International Union of Radio
Science (URSI), Toronto, Canada, August 13-21, 1999.
42) Long-term variations in midlatitude E region coherent backscatter and a relation to
planetary wave activity in the lower thermosphere, C. Haldoupis, M. Voiculescu, K.
Schlegel, and D. Pancheva, XXVI General Assembly, International Union of Radio Science
(URSI), Toronto, Canada, August 13-21, 1999.
43) Evidence for planetary wave role in midlatitide backscatter and sporadic E occurrence, M. Voiculescu, C. Haldoupis, and K. Schlegel,
9th International EISCAT workshop, Wernigerode, Germany, September 6-10, 1999.
APPLIED RESEARCH ON WIND ENERGY
Studies of Wind Potential (under preparation)
Electronic WIND ATLAS of Crete
