Using the Tiny Ionospheric Photometer TIP on the COSMIC Satellites to Characterize the Ionosphere

1
Using the Tiny Ionospheric Photometer (TIP) on
the COSMIC Satellites to Characterize the
Ionosphere

• K. F. Dymond, S. A. Budzien, and C. Coker
• Naval Research Laboratory
• Washington, DC

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Overview

• What Is the Ionosphere?
• What Is the Tiny Ionospheric Photometer?
• What Does Tiny Ionospheric Photometer Measure?
• How Will the Tiny Ionospheric Photometer
  Measurements Be Used?

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What Is the Ionosphere?

• The Ionosphere Is the Section of the Earths
  Atmosphere Where Ions Electrons Naturally Occur
• Altitude Range 60 km Higher
• Produced by Photoionization of the Neutral
  Atmosphere by Solar Radiation
• Balanced by Recombination (Loss Process)

• Most Variable Component In The Atmosphere
• Highest Amplitude to Solar ( Other) Forcing
• Varies With Local Time 10X
• Varies With Latitude 10X
• Varies With Season Solar Cycle 10X
• Spatial Variations
• Global, Regional, Local

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What is Tiny Ionospheric Photometer?

• TIP Sensor Assembly (TSA) TIP Interface/Control
  Electronics (TICE) Module

• Internal Layout of Sensor Head

UV Light
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What Does Tiny Ionospheric Photometer Measure?

• Measures Intensity of Naturally Occurring Airglow
• Caused by Decay of Nighttime Ionosphere
• Produces Light at 135.6 nm Atomic Oxygen
• Why Only at Night?
• Daytime Signals Are Contaminated by Other
  Signatures
• COSMIC Requires a Simple, Very High Sensitivity
  Instrument
• Simple Low Cost, Low Weight, Low Power
• High Sensitivity
• Required to Produce Data of a Quality Comparable
  to GPS Occultation Measurements
• Measure Gradients When Signals Are Weak

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TIP / GPS Occultation Concept
COSMIC Orbit Track
TIP Line-of-Sight
GPS Occultation Ray Path
COSMIC
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Photometer Characteristics

• Sensitivity Is gt300 Counts s-1 Rayleigh-1 (15
  Times Sensitivity of SNOE Aurora Photometer)
• Nightglow Signals Range from 0.1 10 Rayleighs
  (Peak Electron Density 1105 cm-3 1106 cm-3
  for These Intensities)
• Greater Than 3 s Detection for nmax gt 5104 cm-3
  During a 1 s Exposure (gt 3 s Detection for nmax gt
  3104 cm-3 During a 10 s Exposure)
• Field-of-View 4 (Circular)
• 60 Km Diameter (At Earths Surface) from a
  Vehicle at 700 Km Altitude
• 30 Km Diameter At 300 Km Peak Altitude (Typical
  Ionospheric Peak Height) from a Vehicle at 700 Km
  Altitude

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How Will the Tiny Ionospheric Photometer
Measurements Be Used?

• Primary Goal Provide Accurate Characterization
  of Ionospheric Electron Density Gradients
• GPS Occultation Measurements of Electron Density
  Can Be Inaccurate Due to Gradients
• TIP Measurements Can Be Used to Correct for
  Gradients
• Secondary Goals
• Location of Auroral Oval TIP Measured 1356 Å
  Emission That Is Produced by Aurorae
• Location of Appelton Peaks Position of Peaks
  Related to Ionospheric Dynamics
• Add to Ionospheric Climatology Database

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TIP Products
Level 1 Product Nadir Radiance

• Level 0 Product
• Number of Photons Detected Each Second
• Proportional to the Line-of -Sight Integral of
  the Square of the Electron Density
• Level 1 Product
• Along-Track Radiance at 135.6 nm
• Level 2 Products
• Location of Auroral Oval
• Location of Appelton Peaks
• Provisional Peak Electron Density
• Vertically Integrated Square of the Electron
  Density
• Level 3 Products
• Electron Density Maps

Level 3 Product Global Electron Density
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COSMIC Ionospheric Measurements
GOX
TIP
TEC Total Electron Content (cm-2) S(GPS)
Distance From COSMIC to GPS ne Electron
Density s Distance Along Line-of-Sight
4pI Radiance in Rayleighs a Recombination
Rate Coefficient ne Electron Density nO O
Density z Altitude
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Gradient Accuracy (1 of 3)

• How Accurate Are the TIP Gradient Measurements?
• There Are Three Factors Affecting the TIP
  Measurements
• Peak Density
• Peak Height (Very Weak Dependence, Ignored)
• Thickness of the Ionosphere
• We Have Assessed the Effect of All Three
• Generated an Ionosphere Using IRI-90 Simulated
  TIP Measurements
• Following Results are for Equinox Conditions at
  Solar Maximum
• Results Applicable for Solar Minimum, Appropriate
  to Expected COSMIC Flight Conditions

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Gradient Accuracy (2 of 3)

• The Integral Can Be Evaluated to Yield (Where nm
  Is the Peak Electron Density H is the Plasma
  Scale Height)
• Density Gradient Can Be Expressed as Follows

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Gradient Accuracy (3 of 3)
Derivative of the Intensity Gradient

• The Electron Density Gradient Is Well
  Approximated by the Intensity Gradient!
• Can Estimate nm if H Can Be Determined
• Can Accurately Correct GPS Occultation Electron
  Densities for Density Gradients

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TIP Assessment

• Gradient Accuracy Compared the Accuracy of the
  Simulated Gradients With the Variations in the
  F-Region Peak Density
• Demonstrated Use of TIP Data Simulated GPS
  TIP Data Inverted the Data Sets Using Three
  Techniques
• Abel Inversion of GPS Data (Spherical Symmetry
  Assumed)
• Iterative Inversion of GPS Data (Spherical
  Symmetry Assumed)
• Full Two-Dimensional Inversion (Spherical
  Symmetry NOT Assumed)

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Simulation of Electron Density Determination

• Simulated GPS TEC Nadir Photometer Intensities
• Included All Known Physical Effects
• IRI-90 for Ionosphere
• MSIS-86 for Neutral Oxygen Density
• Simulated Occultation Occurred Near 28 N
  Fairly High Gradient
• TIP Simulation Assumed 100 ct/s/Rayleigh
  Sensitivity (Lower Than Predicted)
• GPS Simulation Assumed GPS Uncertainties
  Consistent With Hajj et al. (International
  Journal of Imaging Systems Technology, Vol. 5,
  174-184, 1994.)
• Inverted the Data Using Discrete Inverse Theory

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Inversion Results Comparison
Two-D Retrieval
Input Ionosphere
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Inversion Results (Arcs, Density)
Two-D Inversion Produces a More Accurate Electron
Density Profile Than Spherically Symmetric
Inversions Using GOX TEC Data Alone!
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Concluding Remarks

• Use of TIP Data Can Significantly Improve
  Determination of Nighttime Ionospheric Electron
  Density
• Instruments Are Low Cost, Low Mass, Low Power,
  Low Data Rate, High Sensitivity, and Inexpensive
• TIPs Design Technology Are Mature
  Well-Understood
• Use of TIP, TBB, GPS Occultation Will Provide
  Very High Quality Ionospheric Data
  Significantly Enhance State of Ionospheric
  Science

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Supplementary Slides
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Inversion Results (Arcs, TEC)
Input TEC Retrieved TEC
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Inversion Results (Arcs, Nadir Intensity)
Input Intensity Retrieved Intensity
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Data Inversion

• Full Two-Dimensional Inversion
• Parameterized the Ionosphere Using 5 Parameter
  Chapman Layers
• 4 Parameters to Describe Variation With Altitude
  (Shape)
• Altitude Variation Was Assumed to Be Constant
  Along Satellite Track (Consistent With Gradient
  Plots)
• 56 Parameters Scale the Peak Electron Density at
  Every Degree of Latitude Along the S/V Track
• GPS TIP Data Are Inverted Simultaneously
• Compared the Results to 1 - D Inversions
  (Spherical Symmetry)
• Abel Type (Direct Inversion)
• DIT With 5 Parameter Chapman Layer (Iterative
  Inversion)

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How the Upper Atmosphere Affects Us

• Two Most Obvious Ways
• Ionosphere ? Free Electrons ? E-M Propagation
• Thermosphere ? Gas Density ? Satellite Drag
• Less Obvious Ways
• Auroral Current Systems
• Reactive Ions/atoms and Space Hardware
• Spacecraft Charging

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The Big Picture

• Earth Is in a Stormy Environment
• Solar Particles (Solar Wind, Coronal Mass
  Ejections)
• Solar Radiation (X-rays, Ultraviolet, Visible
  Light, Etc.)
• Space Weather Directly Affects Our Atmosphere
• High-energy Solar Emissions Highly Variable

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Thermosphere Composition

• Homosphere, Well-mixed
• Same Basic Composition As Ground-level
• Heterosphere, No Mixing
• Densities Too Low
• Too Few Collisions
• Composition Varies With Altitude
• Composition of Neutral Atmosphere Affects Ion
  Composition

Heterosphere
Homosphere
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Inversion Results (Arcs, LOS)
Every 10th Photometer Integration (Vertical
Lines) Occultation (Curves) Are Shown