1. SSAEM Sensors
Paul R Straus
October 14, 2011

2. SSAEM KPPs, KSAs, and Programmatic Focus
Ionospheric Scintillation: Communication/Navigation Outages
Electron Density Profile: Ionospheric Specification/Forecasting
KPPs directly drove SSAEM program’s focus on equatorial region
Where ionospheric scintillation is most significant
Where ionospheric densities are highest and have significant variability
KSAs: Chosen to support “KPP areas” based on C/NOFS heritage
In-Situ Plasma Fluctuations: indirectly helps specification of scintillating regions
Electric Fields: driving forces relevant to both specification and forecast of scintillation/ionospheric structure (especially with Full Physics GAIM)
In-Situ Plasma Temperatures: relevant to ionospheric models

3. SSAEM/COSMIC-2 Sensors & EDRs
TriG GNSS Radio Occultation Sensor
TEC, EDPs, L-Band scintillation
RF Beacon
400/~960*/~2200* MHz beacon utilizing SCINDA ground sites
Local TEC, UHF/L-band scintillation
Velocity, Ion Density & Irregularities (VIDI) Sensor
In-Situ Plasma Fluctuations, Electric Fields & Plasma Temperatures
TriG will be on all COSMIC-2 satellites
RF Beacon & VIDI will be on the low inclination COSMIC-2 satellites
*Frequencies TBD

4. SSAEM Approach to Addressing Operational Scintillation/Ionospheric Specification Issues
Measure it
UHF/L-Band/S-Band: RF Beacon/Upgraded SCINDA
L-Band: TriG
Infer it
In-Situ Plasma Fluctuations & Depletions: VIDI
Models incorporating the deriving forces (PBMOD): VIDI
Ionospheric Structures
TriG & RF Beacon/SCINDA
In-track Plasma Density: VIDI
Models incorporating driving forces (e.g., Full Physics GAIM): VIDI
Primary approach for KPP

5. VIDI Instrument Objectives & Approach
Measure in-situ plasma parameters related to ionospheric specification and scintillation
3D plasma drifts (used to infer Electric Fields)
Cross-track drifts to ±5 m/s accuracy
In-track drifts to ±10 m/s accuracy
Electron/ion density & composition (both to 5% accuracy)
Electron/ion temperature (to 10% accuracy)
Plasma density fluctuations (to 10% accuracy at 15 m horizontal resolution – 512 Hz sample rate)
Approach: Gridded sensor apertures on the ram face of the spacecraft collect and analyze electron/ion (dependent on grid potentials) currents from the ambient plasma environment to enable determination of environmental parameters

6. VIDI/IVM Sensor Electronics and Aperture Plate

7. VIDI/SPLP Sensor Electronics and Aperture Plate

8. Density fluctuations observed by PLP
VIDI In-Situ Sensor
Observe/characterize in-situ structures associated with scintillation
Horizontal measurement of density fluctuations can be used to estimate S4 scintillation parameter
Observations of plasma drifts (Electric Fields) can be used to drive ionospheric models
SatCom/GPS
Satellite
Density fluctuations observed by PLP
Irregularities
in Ionosphere
A Planar Langmuir Probe (PLP) will directly address the two KPPs of scintillation and Electron Density Profiles (EDPs) in a simple affordable manner.
Scintillation: Scintillation is caused by chaotic fluctuations in the index of refraction along a path between a satellite and a ground receiver produced by turbulent plasma. It is not practical to directly measure the plasma density along a vertical path, but it is easy to measure the plasma density along a horizontal satellite track. The horizontal density structures observed by PLP can be translated into a vertical distribution of density fluctuations and used to calculate the level of scintillation that an observer on the ground would see. This measurement would provide global equatorial coverage of the presence of scintillation ever 90 minutes.
EDPs: PLP does not directly measure vertical electron density profiles but provides a point of truth that can be used to guarantee that model outputs of the ionosphere are correct.
Scintillation,
comm dropouts,
GPS loss of lock
In-Situ observation
Climo
Receiver
Model w/ E-field

9. RF Beacon Instrument Objectives & Approach
Enable measurement of equatorial scintillation (in concert with a network of ground receivers) throughout the UHF/L-band frequency range
Separate UHF & L-band frequencies required
S-band frequency to provide stable reference for phase scintillation measurements under strong scintillation conditions
S4 & σφ measurements required to 0.1 & 0.1 radians uncertainty, respectively
Enable measurement of slant-path TEC using ground receivers
Measurement Accuracy of 0.01 TECu for relative TEC (threshold)
Measurement Accuracy of 3 TECu for absolute TEC (objective)

10. RF Beacon
Ground-based measurements of scintillation using SSAEM Beacon signals will enhance probability of scintillation detection and improve temporal and spatial resolution relative to current SCINDA products
Beacon TEC measurements provide ancillary data for GAIM
Beacon Data
SCINDA RADAR MAP
2+ hour forecast for scintillation downstream
Current Product
Improved Product
A satellite beacon/receiver pair provides an observation of what is below the satellite. However it requires ground assets (either ground-based receivers or transmitters).
This was a single example of how addition structures were detected when a beacon passed over a SCINDA site.
SCINDA SPECIFICATION MAP
Single look direction to GEO satellite
Increased spatial coverage with beacon
Current Product
With Beacon

11. Coverage/Refresh Analysis for Scintillation Specification/Prediction
Analysis performed to assess performance of COSMIC-2 (equatorial component) relative to single free flyer & scintillation development time scales
Mapping of irregularity regions along geomagnetic field lines results in excellent performance

12. Scintillation Coverage vs. Refresh
COSMIC-2
Free-Flyer
RF Beacon
SCINDA Ground Stations
COSMIC-2
30N
30S
Existing Sites
UN IHY Sites
Other/collaboration
COSMIC-2
Scintillation Evolution
Time Scale: minutes
Free-Flyer
TriG
COSMIC-2
SSAEM Will Completely Characterize the Equatorial Scintillation Environment
Free-Flyer
VIDI (Fluctuations)

13. CORISS/ALTAIR Geometry
21 Apr :09 UT
Tangent Point Track
C/NOFS Orbital Track
Apex Altitude km 13

14. Coherent Returns from ALTAIR & CORISS SNR
CORISS occultation
tangent points
CORISS SNR
Bottomside
Max Height
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. 10

15. CORISS Observations & Simulation
Assume weak scattering:
PRN 16
Given propagation orthogonal to B, then
where d is C/NOFS-GPS distance
Yields ds ~ 630 km (t.p. is ~500 km)
Determine irregularity strength, region size, spectral slope, & BG density profile from ALTAIR, SCINDA & CORISS measurements
Fresnel null frequencies
Multiple Phase Screen Simulation
CORISS
Break frequency 15

16. Multiple Phase Screen Simulation of CORISS Data
MPS Simulation
CORISS 15

17. Coverage/Refresh Analysis for Ionospheric Specification/Prediction
Analysis assumptions:
Evaluation of ability to “populate” a GAIM-like model
1°×2.5°×20-50 km voxel granularity
In-situ density observations provide exact specification of voxel density
TriG TEC observations provide data for tomographic-like reconstruction
Require two observations through a voxel to be considered fully specified
Analysis region: ±30° geomagnetic latitude range over km altitude range, bounded by 300 km field lines at ±30°

18. Ionospheric Specification Coverage vs. Refresh
COSMIC-2 will cover 50% of the equatorial region every hour
Only includes equatorial component of COSMIC-2 constellation: actual performance will be better
If Electric Fields can be utilized in operational model, performance may improve due to leveraging of physics of magnetic field mapping
COSMIC-2
Free-Flyer
TriG+VIDI (In-Situ Density)
Bulk Ionosphere Evolution
Time Scale: ~60 minutes
COSMIC-2
SSAEM Will Measure Both the Background Ionosphere and the Most Significant Driving Force Relevant to Low Latitude Ionospheric Modeling
Free-Flyer
VIDI (E-Fields)