© 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

Tangent Point Track

Apex Altitude 300-400 km

C/NOFS Orbital Track

21 Apr 2009 10:09 UT

CORISS/ALTAIR Geometry

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

• 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

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

“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

Summary of CORISS (L-Band)/SCINDA (UHF) Comparisons

“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