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© The Aerospace Corporation 2010
Radio Occultation Sensor Observations of Ionospheric Scintillation
P. R. Straus1, C. Carrano2, R. Caton3, K. Groves3 , and
R.L. Bishop 1The Aerospace Corporation2Boston College3Air Force Research Laboratory
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Overview
• CORISS-Radar-Theory evaluation of RO scintillation observation
• Calculation of S4
• “Proxy” S4 indices
• Ground UHF/RO scintillation comparison
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Tangent Point Track
Apex Altitude 300-400 km
C/NOFS Orbital Track
21 Apr 2009 10:09 UT
CORISS/ALTAIR Geometry
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Coherent Returns from ALTAIR & CORISS SNR
•ALTAIR indicates location of small-scale (40cm) irregularities relative to the CORISS tangent point track. CORISS detects ionospheric irregularities only within F region, while high sensitivity of ALTAIR reveals structure at slightly lower altitudes.•Mean scattering location is slightly westward of the CORISS tangent point track.
CORISS occultation tangent points
CORISS SNR
Bottomside
Max Height
10
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• Assume weak scattering:
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2scan
sb
Vd
f
Break frequency
Fresnel null frequencies
• Given propagation orthogonal to B, then/ /C NOFS GPS C NOFSs
scan
dV V V V
d
• Yields ds ~ 630 km (t.p. is ~500 km)
• Determine irregularity strength, region size, spectral slope, & BG density profile from ALTAIR, SCINDA & CORISS measurements
where d is C/NOFS-GPS distance
PRN 16
CORISS Observations & Simulation
CORISS
Multiple Phase Screen Simulation
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MPS Simulation CORISS
Multiple Phase Screen Simulation of CORISS Data
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Proper Calculation of the S4 Index
• What sample rate should be employed?
• How long a data segment should be analyzed?
• The answer depends on the Fresnel frequency– Optimally, one should observe at a frequency substantially above fFresnel
and calculate S4 over a sample interval 10 longer than 1/fFresnel
– For occultation data 50 Hz observations are adequate with a 10 second sample interval
• RO data does not support calculation of S4 over a 1-second interval
• Data must also be detrended prior to calculating S4
2
22
4i
ii
P
PPS
2)(SNRwhere Pi is the receiver power
zv
f zFresnel
2
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“Proxies” for S4: SRO (1s)
• Calculated from MR (1 Hz) C/A SNR observations
1 Hz Data50 Hz Data
PRN27 @2009/03/30 05:10:00
SRO(1s) (31 s)S4 (10 s)
C/A
SN
R
SR
O(1
s)
S4 (10 s)
All profiles with max(SRO(1s)) > 0.5
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Summary of CORISS (L-Band)/SCINDA (UHF) Comparisons
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“Proxies” for S4: UCAR S4 (COSMIC)
• Calculated from on-board 50 Hz SNR variance collected at 1 s cadence
S4 (1s) UCARS4 (10s)
C/A
SN
R S4
(1 s
)
PRN27 @2009/03/30 05:10:00
S4
(10
s)
S4 (10s) UCARS4 (10s)
All profiles with max(SRO(1s)) > 0.5
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Summary
• CORISS high rate observations of scintillation are in the process of being validated through ground/theory comparisons
• SRO(1s) calculated from 1 Hz SNRs generally under-predicts S4, but is fairly representative of S4 characteristics most of the time
– The lower noise floor is useful for certain types of analysis
• UCAR (COSMIC) 1-second S4 index is not valid, but the UCAR approach to S4 determination can be made to work quite well if calculations are extend over a larger time interval (10 s)
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Simulation of Scintillation in a Limb Viewing Geometry
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Single Bubble Simulation
zv
f zFresnel
2
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Multi-Bubble Simulation