Solar Radiophysics with HF Radar

Solar Radiophysics with HF Radar
Workshop on Solar Radiophysics
With the Frequency Agile Solar
Radiotelescope (FASR)
23-25 May 2002
Green Bank, WV
Paul Rodriguez
Information Technology Division
Naval Research Laboratory
Washington, DC
The Solar & Lunar HAARP
Radial
Distance
1 AU
0.5 AU
Range of Space Experiments with HF Radiowaves
Solar Corona
Detection of CMEs & prediction of geomagnetic storms
Densities, temperatures of solar corona
Large scale structure, dynamics, wave spectrum
Planetary Surfaces
Detection of near earth asteroids, comets
60 Re
30 Re
Selenosphere
Lunar surface penetration by HF radiowaves
Charged lunar dust atmosphere?
Lunar wake structure
Solar Wind
Solar wind large scale density structures
Bow shock irregularities and dynamics
15 Re
Magnetosphere
0.05 Re
Ionosphere
Boundary and global scale dynamics
Response to geomagnetic storms
Magnetospheric wave-particle interactions
Modification (growth and decay scales of irregularities)
Long distance radiowave propagation
Density irregularity spectrum
Meteor showers (Leonids; dusty plasmas)
0.1 MW
1 MW
10 MW
100 MW
Effective
Radiated
Power
1000 MW
El Campo, Texas Solar Radar Antenna Array
Operated by
MIT/Lincoln Laboratory
1961-1969
S
E
W
N
Operating Frequency:
Transmitting Dipoles:
Receiving Dipoles:
38.25 MHz
128 x 8 EW
128 x 8 EW
128 x 4 NS
Total Area:
18,000 m2
Antenna Gain:
32-36 dB
Beam Size (NS x EW):
1o x 6 o
Total Power:
500 kW
Effect. Radiated Power: 1300 MW
Motivation for initial solar radar experiments
•
to determine radar cross section of the solar corona
(however, it was recognized there was no ‘hard surface’ )
•
to investigate dynamics of solar corona
Present scientific motivation
•
profile of corona electron density
•
backscatter from a hot, magnetized plasma
•
remote sensing of wave-particle interactions in the corona
(small scale dynamics)
•
measurement of large scale MHD (i.e., CMEs)
•
understanding of nonthermal development of various
spectra (density fluctuations, waves, radio, etc)
•
direct measurements of stellar plasma and how it affects
planetary environment
Solar Radar Performance
The radar equation is
Pt Gt
Pr =
where:
4πR
Pr
Pt
Gt
Ar
-
Ar σ p
2
4πR
received power (watts)
transmitted power (watts)
transmitting antenna gain
receiving antenna area (m2)
2
σ - scattering cross-section (m2)
p - polarization fraction
R - range to scattering cross-section (m)
Ro - solar radius (m)
R = 1.5 x 1011 m (1 AU)
Ro = 7 x 108 m (solar radius)
σ ~ 1 π Ro2 = 1.54 x 1018 m2 ( typical value obtained by El Campo)
p = 0.5 (one of two polarizations)
N = kB T(f) B (noise power of sun), where
kB = 1.38 x 10-23 watt-s °K-1 (Boltzman’s constant)
T(f) = noise equivalent temperature of sun (°K)
B = receiver bandwidth (Hz)
El Campo Solar Radar (38.25 MHz)
40
o
2
Cross Section (πR )
50
30
20
10
0
21000
21500
22000
22500
23000
23500
24000
30 Jun 61
12 Nov 62
26 Mar 64
8 Aug 65
21 Dec 66
4 May 68
16 Sep 69
Serial Day
Day Month Year
El Campo Corona Echo Signal Spectrum
Typical RDA spectrum.
Among spectral types
observed were
“high corona echoes,”
which may have been
CME signatures.
However, CMEs were
unknown in the 1960s.
Solar Radar Detection of Earthward-Directed
Coronal Mass Ejections
CME
Solar
Radar
Transmitted
Power
Received
Corona
CME
Frequency Shift
HF Doppler Shift from Earthward Motion
of Coronal Mass Ejection
400
Frequency Shift (kHz)
f Dp (9 MHz)
f Dp (25 MHz)
f Dp (38 MHz)
300
200
100
0
0
200
400
600
800 1000 1200 1400 1600
CME Velocity (km/s)
The Doppler shifts expected for HF radar
frequencies of 9, 25, and 38 MHz, for the range
of CME velocities observed with coronagraphs.
Solar Radar Experiment 21 July 1996
8.920 MHz
Full
Power
ON/
OFF
10
SURA Transmitted Signal UT 0911-0927
20
30
40
50
60
seconds
40
50
60
seconds
8.880 MHz
0
10
20
30
UTR-2 Return Signal Spectra UT 0927-0943
44
Frequency
Shift (kHz)
8.925 MHz
0
-10
OFF
0
ON
10
-10
ON
0
OFF
10
44
Frequency
Shift (kHz)
8.885 MHz
0
Time (sec) Relative to Transition
Integrated Return Signal Time Profiles and Spectra
SURA / UTR-2
10
8.885 MHz
Relative Intensity
21 July 1996
Transmission
Patterns
8.925 MHz
ON
8
OFF
6
4
ON
OFF
2
0
-10
-5
SURA / UTR-2
Relative Spectral Intensity
Solar Radar
0
Time (sec)
Solar Radar
5
10
21 July 1996
6500
8.925 spec
8.885 spec
6000
5500
5000
4500
0
5
Receiver
Frequency
10
15
20
25
30
35
Frequency Shift (kHz)
40
HAARP Research Facility
Gakona, Alaska
Operated by Advanced Power Technologies, Inc.
under contract from U. S. Air Force/ Navy
Current
Radiating x-dipoles:
48
Total area (m2):
20,000
Transmitters:
96
Power (kW):
960
ERP (MW):
190
Frequencies (MHz):
2.8 to 8
Design
180
124,000
360
3600
3200
2.8 to 10
Sun As Seen From HAARP at
UT 2000 (o), 2100 (◊), 2200 (∆), 2300 (x)
LT 1100 (o), 1200 (◊), 1300 (∆), 1400 (x)
90
80
Altitude (deg)
70
Solar Radar Window
60
50
40
30
20
10
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
0
30
61
91
122 152 182 213 243 274 304 335 365
Day of Year (2000)
LOFAR: CONCEPTUAL
LAYOUT
LOFAR will be:
~ 1 meter
Active dipole
• ≥ 40 stations
Los Alamos
• ≥ 10,000 dipoles
• ≥ 1 km2 collecting area
– 20x Arecibo
Ground Screen
VLA
Each
LOFAR Station
consists of
256 Active Dipoles
above their ground
screens
~ 160 m (5 acres)
• ∆ν ~ 10-250 MHz
• ≥ 2 independent beams
New Mexico
Possible LOFAR
Station sites
HALO Solar Radar
30
HAARP Frequency = 10 MHz
Net Signal/Noise Ratio (dB)
25
LOFAR Effective Area ~ 106 m 2
Solar Radar X-Section = 1
20
Total
Power
(MW)
15
10
3.2
5-dB
Threshold
5
0
0.9
-5
Initial HAARP
Power
0.3
-10
0.
1
Present HAARP Power
Design HAARP Power
10
100
Integration Time (s)
1000
10000
Summary and Conclusions
•
Solar radar experiments will ‘open’ a new window on
plasma physics of the sun and magnetosphere.
•
Solar radar has applications to many other phenomena of
local astrophysics.
•
HAARP is capable of being a solar radar, in bistatic
configuration with existing and planned receiving arrays.
•
The CME detection problem and geomagnetic storm
effects at earth is a practical motivating issue.

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