An In Situ ElectronDensity Database Derived from Passive RPI Observations

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An In Situ Electron-Density Database Derived from
Passive RPI Observations

• Phillip A. Webb
• Goddard Space Flight Center
• Greenbelt, MD

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Collaborators

• Robert Benson, NASA/GSFC.
• Richard Denton, Dartmouth College.
• Jerry Goldstein and Jillian Redfern, SwRI.
• Leonard Garcia, QSS Group Inc.
• Plus thanks to Dr. Bodo Reinisch (RPI PI),
  University of Massachusetts Lowell.

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The Plasmasphere
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Radio Plasma Imager (RPI) Instrument

• Operates from 3 kHz to 3 MHz.
• Range covers plasma resonance frequencies
  characteristic of the Earth's magnetosphere.
• Spin-plane X and Y antennas - 0.321 mm thick,
  500 m tip-to-tip length.
• Spin-axis Z antenna, 20 m lattice booms.
• IMAGE is spin-stabilized (2 minute).

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Active RPI Observations

• Pulsed transmissions from the X dipole.
• Received measurements on each antenna are
  displayed in "plasmagrams".
• Determine electron cyclotron frequency (fce) (to
  within 0.1) and electron plasma frequency
  (fpe) (to within 1) from the stimulated plasma
  resonances and the Z- and X-mode wave cutoffs
• Benson et al., 2003 JGR

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IMAGE/RPI Active Plasmagrams
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Passive RPI Observations

• Display signals from space-plasma emission
  processes.
• Measurements displayed in dynamic spectra
• Composed of spectral line scans ( 2 minute
  separation).
• Use combined signals from the X and Y dipoles -
  smoothes out antenna spin-modulation effects.

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Superimposed Active and Passive Observations
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The Upper-Hybrid Band Active- passive comparisons
Active
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Dynamic Spectra ExampleSeptember 2, 2002
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1) Set the Search Boundaries
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2) Locate n1/2 Emission Bands
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3) Search for Upper-Hybrid Peak
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4) Search for Continuum Band
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5) Refit Data Drop-outs
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6) Refit Peaks Previously Determined to be
Incorrect
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7) Refit Possible fpe Gradient Errors
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Example of Manually Corrected Fit
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Data Output

• Generates plots of fpe fits for each orbit.
• Generates ASCII formatted file that contains
• orbital parameters (e.g., UT, radial distance)
• fitted parameters (e.g., fpe, number of n1/2
  emission bands)
• fitting options used (e.g., maximum L-shell,
  dB/Hz0.5 drop used with flo/fup)
• Ne ? fpe2/80.6

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Plasmaspheric Features
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The Database is Released into the Wild!

• Alpha version.
• Covers period from January 2001 through to August
  2004.
• Contains 147,000 fpe data points.
• Represents 306 continuous days of data.
• Envisage use is from data on specific days
  through to climatological studies encompassing
  one or more years.

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Distribution of Data
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Electron Densities
C A Saturated Model
C A Plasmatrough Model
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Future Development Plans

• Complete the fitting of the RPI dynamic spectra
  from 2001 to 2005.
• Improve the fitting approach - an ongoing
  process!
• Look at applying the fitting technique to other
  dynamic spectra data bases such as Hawkeye, DE,
  Polar, CRRES, Wind, etc.
• Last week I won NASA NIP funding to do all of the
  above - so it will happen!