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Transcript of 1 Receiving Ground-based VLF Transmissions with RPI on IMAGE Bodo W. Reinisch Environmental, Earth,...
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Receiving Ground-based VLF Transmissionswith RPI on IMAGE
Bodo W. ReinischEnvironmental, Earth, and Atmospheric Sciences Department
Center for Atmospheric ResearchUniversity of Massachusetts Lowell
AFRL Hanscom AFB
19 December 2002
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IMAGE Spacecraft
500-m dipoles in spin plane
20-m dipole along z
<10 W radiated power3 kHz – 3 MHz300 Hz bandwidth
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Cavity
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Overview of Radio Plasma Imager (RPI)
• RPI transmits coded EM waves and receives echoes at 3 kHz to 3 MHz
– Uses advanced digital processing techniques (pulse compression & spectral integration)
• RPI uses a tri-axial orthogonal antenna system– 500 meter tip-to-tip X and Y axis dipole antennas– 20 meters tip-to-tip Z axis dipole antenna– X axis antennas are used for transmissions– Echo reception on all three
• Basic RPI measurements of an echo at a selected frequency – Amplitude– Time delay (distance or range from target)– Direction of arrival– Wave polarization (ordinary or extra-ordinary)– Doppler Spectrum
• In situ density and resonances measurements
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Timing, Digitizer & Synth (DC1)
+Z De-ployer
CIDPMulticonductor Cable
RF Amp/Coupler
+Y Deployer
Oscillators, Exciters & Z Receiver (AN1)
RS-422
Secondary Power Distribution (SPD) (includes serial comm port)
RF Coax
Transmitter Power Distribution (TPD)
TMS320C30 DSP - based CPU (SC7)
Rcvr Preamp
+X Deployer
-Y Deployer
-X Deployer
VME Bus
X & Y Receivers (AN2)
Preamps
-Z De-ployer
Rcvr Preamp
RF Amp/Coupler
Rcvr PreampRcvr Preamp
RF Amp/Coupler RF Amp/Coupler
VME Bus
VME Bus
VME Bus
VME Bus
BeCu Wire
VME Chassis
10 mBoom
10 mBoom
250 mAntenna
250 mAntenna
250 mAntenna
250 mAntenna
RPI Block Diagram
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Transmission with Tuned Antennas
V a £ 1.5 kV rm s
T ra n sm itter C o u p ler
1 /2(R a + iX a)
A n ten n am o n o p o le
1 /2(R c - iX a)
6- 24 V
0 V
5 V
0 V
5 V
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RPI SpecificationsItem Specification Comments
Radiated power 10 W Tuned Antennas
Antennas 3 orthog. dipoles 2 x 500 m, 20 m
Frequencies 3 kHz - 3 MHz 10-1 - 105 e/cm-3
Bandwidth 300 Hz Matched
Pulse Width 3.2 ms Range resolution
Range Resolution 480 km
Range 20 RE SNR dependent
Angular Resolution 2o 500 km res. at 2 RE
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Local plasma resonances
X-mode echo trace
Sounding in the Polar Cap
S/CZ trace
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Field-Aligned Propagation Plasmagram
[Reinisch et al., GRL, 4521, 2001]
SX from southern HP
NX from northern HP
SX+NX double reflectionRecalculatedEcho traces
Plasma resonances
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Empirical Magnetospheric Density Distribution
Average2000-2001
L = 7
6
5
June 20010800 LT
March 20011200 LT
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05 Apr 2001
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20
30
40
50
60
70
210 240 270 300 330
Maine, NAA 44.5 N, 291 ESeattle, NLK 48.0 N, 238 EAustralia, NSW 32.0 S, 116 E
year 2001
0424 UT
0600 UT
0438 UT
March 26
1600 UT
1544 UT
1400 UT
IMAGE B-field projection
April 4
0056 UT
0034 UT
2300 UT
February 14/15
NLK
NAA
GEO Longitude, deg
GE
O L
atit
ud
e,
de
g
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Seattle, NLK 24.8
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Seattle, NLK 24.8
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Seattle, NLK 24.8
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Maine, NAA 24.0
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Australia NSW19.8
Maine NAA 24.0
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Backup
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Antenna Coordinates and Wave Polarizations
y
x
z
z'
e-wavei-wave
B0
y'x'
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Quadrature Samplesy'
x'
E Q = E R (w t=p/2 ) E I= E R (w t= 0 )
a0R
a
b
Reinisch et al., Radio Sci. 34, 1513-1524, 1999
Reinisch et al., Space Sci. Rev. 91, 319-359, 2000
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The Wave Normal
Reinisch et al., Radio Sci. 34, 1513-1524, 1999
Reinisch et al., Space Sci. Rev. 91, 319-359, 2000
I Q
I Q
x
x
Ε Ε
Ε Εn
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Wind – RPI
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Signal Transmitted byRPI
Signal Received byWBD
IMAGE to Cluster Radio Wave Transmission Experiment, 23 April 2002
Received Waveform with Fitted Pulse and Background Levels
04:44:37 04:44:39 04:44:41 04:44:43
E (
mic
rovo
lts
/ m
)
-1.0
-0.5
0.0
0.5
1.0
E (
mic
rovo
lts
/ m
)
-1.0
-0.5
0.0
0.5
1.0
-1.5
1.5
SC
2 S
als
aS
C3
Sam
ba
Spectrograms of Received Signal at Each Spacecraft
04:41:00 04:41:30 04:42:00 04:42:30 04:43:00 04:43:30 04:44:00 04:44:30
Ez
Fre
q [
kH
z]
502
504
506
508
510
Ez
Fre
q [
kH
z]
502
504
506
508
510
Ez
Fre
q [
kH
z]
502
504
506
508
510
Ey
Fre
q [
kH
z]
502
504
506
508
510
10-16
10-15
10-14
10-13
10-16
10-15
10-14
10-13
10-16
10-15
10-14
10-13
10-16
10-15
10-14
10-13
V2m-2Hz-1
SC
4 T
an
go
SC
3 S
amb
aS
C2
Sal
sa
SC
1 R
um
ba
Relative positions roughly to scale
University of Iowa
Funding for this experimentprovided by NASA
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System Parameter Nominal Limits RationaleRadiated Power 10 W @ 5% to
20% duty cycle10 W per antennaelement
Required for adequate SNR
Frequency Range 3 kHz – 3 MHz Covers expected range of plasmadensities.
Freq. Accuracy1x10
-5 Accurately measures observed plasmadensities
Freq. Steps 5% steps 100 Hz 5% in frequency gives 10% in plasmadensity resolution.
Measurement Duration 1 s to minutes 50 ms Different spatial and temporalrequirements along orbit
Maximum VirtualRange
120,000 km 300,000 km Extent of expected magnetosphericecho ranges
Minimum VirtualRange
980 km w. 3.2 msshort pulses
0 km for passivemodes
Pulse width + receiver recovery time is7 ms
Range increments 240 km 240 or 480 km Required sampling resolutionPulse Rep Rate 1 s-1 0.5 to 20 s-1 Sets unambiguous rangePulse Width 3.2 ms 3.2 ms to 1.9 s Provide 480 km range resolution
Receiver Bandwidth 312 Hz Consistent with 3.2ms pulse widthReceiver Sensitivity 25 nV/Hz (X&Y);
8nV/Hz (Z)Keeps receiver noise below cosmicnoise
Coherent IntegrationTime
8 s 125 ms to 64 sec Provides both processing gain &Doppler resolution
Doppler Resolution 125 mHz Determined by coherent integrationtime
Receiver saturationrecovery
6 ms Specially designed monostatic radarreceiver
Doppler range ±2 Hz 150 Hz To measure expected plasma velocitiesAmplitude resolution 3 dB 3/8 dB Data format allows 3/8 dB, but typical
display is 3 dBAngle-of-Arrivalresolution
2
1 when SNR is
40 dB or better
Identify echo direction with requiredaccuracy
Antenna Length 10 m & 250 m SNR required
Processing Gain 21 dB 0 to 33 dB To enhance weak echoes
Mass incl. Antennas 56 kg
Average Power 32 W
Table 1. RPI Specifications
RPI Specs