Ionospheric HF radars Pasha Ponomarenko. Outline Conventional radars vs ionospheric radars...
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Ionospheric HF radarsPasha Ponomarenko
OutlineConventional radars vs ionospheric radarsCollective scatter processesAspect angle effectsHF propagation featuresSuperDARN
RadarsRAdio Detection And RangingRemote sensing tool based on EM wave emission and its reflection/scatter from a targetMain target parameters:range time of flightdirection antenna directivityvelocity Doppler shift
GroundNormal radarstargetThe target is usually smaller than the spatial pulse length.
Ionospherewith irregularitiesGround~300 kmIonospheric radarsThe scattering volume is larger than the spatial pulse length.
Collective scatter theory /2irregularitiesConstructive interference(Bragg condition)Spatial array with l = /2
Ionospheric turbulenceContinuous spatial spectrum of irregularities
Bragg scatter still works!/2Constructive interference condition(Bragg condition)
Anisotropic turbulenceE and F region irregularities are aligned with the background magnetic field
Dipole antenna with l >>
Aspect conditionsphase front
HF PropagationRadarHF: fN ~ f010-20 MHz
SuperDARNSuper Dual Auroral Radar Network
Dual Radar Network
Things to remeber:Backscatter signals are produced by plasma structures with Bragg scale sizes, l = /2Most of the backscatter power comes form areas where the radio wave propagates orthogonally to the geomagnetic field, k B0HF signals are capable of over-the-horizon propagation due to consecutive reflections from the ionosphere and the ground