Distributed Radar Networks

Ray Greenwald

JHU/APL

Importance of J, E, P , and H

• M-I coupling is all about the ionosphere acting as a dynamic boundary condition to magnetospheric processes

• Magnetospheric electric fields and pressure gradients drive FACs that close in the ionosphere in a self-consistent manner.

• Ionospheric conductances are variable and often highly time dependent.

• Seasonal variability

• Conjugate effects

• Auroral particle precipitation

• To understand the coupling process, we need to measure and understand the self consistency of J, E, P , and H

Importance of E

• E controls the circulation of magnetospheric plasma

• E affects auroral energization

• E controls the circulation of ionospheric plasma and affects the evolution of the ionosphere.

• Large-scale structuring

• Small-scale plasma instabilities

• E transfers momentum to the neutral atmosphere and affects global neutral wind patterns.

• E heats the neutral atmosphere and contributes to plasma outflow to the magnetosphere.

Measurement Techniques and Capabilities

Technique Quantity Measured Derived Parameter Coverage Meas./Instr.

Mags. Magnetic field Currents 100 km 1

ASI Optical emissions <U>, 800 km Many

Fabry-Perot Opt. line shift Neutral wind ???? Several

Ionosonde Reflection delay Ne profile 100-200 km 1

GPS Rx Propagation delay TEC 800 km ~9

HF Radar Irreg. backscatt.(F) Primarily Vd, E 3500 km Many

Others

Why Radars are Good Instruments

• Radars provide you with both range information and angular resolution.

• Range information is provided by the duration of the transmitted signal.

• Limited by sensitivity

• Angular resolution provided by the characteristics of the radar antenna.

• Limited by cost

• Radars can operate under all seeing conditions.

• Radars, particularly obliquely-directed radars have very large fields of view.

• E-region radar – pie section to ~1200 km

• F-region radar(direct backscatter) – pie section to ~2000 km

• HF F-region radar(multihop) – pie section to >3500 km

Importance of Antennas

• The most important element of a radar system is the antenna. Antennas provide:

• Spatial resolution through their directivity

• Sensitivity through their collecting area

• Spatial coverage through their scanning ability

• Modern radar systems often use one or two-dimensional arrays of antennas that are phased electronically to steer the radar beam in one or two dimensions.

• SuperDARN is an example of a one-dimensional phased array that uses horizontally-polarized log-periodic dipole antennas.

• For optimal performance the design criteria of the individual antennas should be compatible with the design requirements of the full phased array.

An ExampleSchematic View of SuperDARN Radar

16 antenna main array

Power AmpsSwitches

Power AmpsSwitches

Power AmpsSwitches

Power AmpsSwitches

Phasing MatrixControl Signals

RF Subsystems

Phasing Matrix

4 antenna interferometer array

Main Processing Computer

Timing Computer

Communications Computer

Internet

~250 m

100 m

Directive Characteristics of SuperDARN Radars

• Both antenna arrays are steered into 16 azimuthal beam directions using capacitive delay line phasing matrices.

• Phase shift between backscattered signals arriving at main and interferometer array used to determine elevation angle of returning signal.

• Combination of azimuth and elevation angles plus range and Doppler spectra characteristics used to specify the location of scattering region.

• Azimuthal beam spacing: 3.15°

• Two-way azimuthal beamwidth: 2.5° - 6°

• Accuracy of elevation angle determination: ~1°.

SuperDARNCurrent Northern Hemisphere Radars

King Salmon

Missing

Prince George

Missing

SuperDARN – An HF Radar NetworkToday and Tomorrow

Northern Hemisphere Southern Hemisphere

SuperDARN web site at Johns Hopkins Applied Physics Laboratory

superdarn.jhuapl.edu

Utilization of SuperDARN Data

SuperDARN Publications

0102030405060708090

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Year

Nu

mb

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More than 380 publications have included SuperDARN data since 1993!

Utilization of SuperDARN Data

S u p e r D A R N R e s e a r c h D i r e c t io n s

G l o b a l C o n ve c ti o n

1 6 %

C o n ve c ti o n D yn a m i c s

1 9 %

S W - M - I- A C o u p l i n g

2 8 %

Io n o s p h e r i c P r o c e s s e s

3 3 %

N e u tr a l W i n d s /W a ve s

4 %

SuperDARNA Homogeneous Global Facility

• All SuperDARN radars have the same basic design and use the same radar control software.

• All radars process the data in the same manner and produce data files with identical formats.

• All operations are preplanned with 70% of the operations performed in a coordinated manner. Operations are continuous (24X365).

• Data from the radars are combined onto DVDs and distributed to the entire SuperDARN community.

• Data from the northern hemisphere radars are collected in near real time to specify the state of the high-latitude convection and high-latitude propagation.

• Products are available on the Internet.

• Scientific data analysis utilizes common routines to assure uniformity of the science results.

Summary

• SuperDARN is a unique international network of HF radars that were developed to understand the large-scale dynamics of the high-latitude ionosphere and magnetosphere.

• Relatively few sites are required to cover very large spatial areas

• SuperDARN has been developed and operated by an enthusiastic group of scientists from 10 countries. Other countries are working to become members of SuperDARN.

• The primary data products from SuperDARN are plasma convection and the ionospheric electric field. Other secondary data products are also important, including gravity waves, planetary waves and mesospheric winds.

• Since 1993, there have been more than 380 scientific publications that have used SuperDARN data. These publications cover most aspects of high-latitude ionospheric physics and magnetosphere-ionosphere coupling.