Electron density profile retrieval from RO data

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Electron density profile retrieval from RO data

• Abel inversion error of Ne
• Data Assimilation test

• Xinan Yue, Bill Schreiner

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Abel Ne Error Sources

• Assumptions used in CDAAC Abel
• 1. Straight-line signal propagation
• 2. Circular satellite orbit
• 3. First-order estimation of electron density at
  the orbit altitude
• 4. Spherical symmetry of electron density

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Orbit Ne estimation evaluation Comparing CHAMP
RO estimated with PLP observed Ne on the orbit
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Current CDAAC estimation method tends to
overestimate the orbit Ne.Since we use the
constant Ne assumption around top most points,
while the Ne decrease with the altitude increase
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Abel 1 First order estimation Abel 2 Given by
on orbit observation (here is the model
result) Abel 3 No orbit Ne
1, Different orbit Ne estimation method will
mainly influence the top most points. 2, Adding
an on orbit Ne observation seems like not
necessary for the Abel inversion.
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Abel Error distribution versus latitude and
altitude Modeling results
True Ne
Retrieved Ne
Noon timeLT13
Absolute Deviation
Relative Deviation
Unit 11011/m3
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COSMIC observations (same time/duration as
simulation)
110 km
220 km
COSMIC
Unit 11011/m3
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Artificial Wave Number 4 structure of Ne below F2
region made by the Abel inversion Simulation
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COSMIC Observations, 20-22 LT
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Conclusion

• The orbit Ne is overestimated by 10 in the
  current CDAAC method from CHAMP observations.
• The orbit altitude Ne only influences the topside
  of the EDP. Adding an on orbit observations has
  no positive effect on the EDP retrieval.
• The Abel inversion can result in some systematic
  errors. e. g. plasma cave, three peak of the E
  layer along the latitude, artificial wave number
  4 structure in the E and F1 layer.

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2.Data assimilation retrieval
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• Assimilation method and parameter choice

• Pijr1XibXjbe-dij/L r10.01
• Rijr2y2dij r20.001

• Grid division
• Latitude2.5 degree Longitude 5 degree
  Altitude 2.5 km
• For one occultation event, there are 6000 grid
  points that GPS rays pass through

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• Ionospheric Correlation Length

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• 2009.266 (very quiet) is chosen to do the test

Background F107
DA1 NeQuick real
DA2 IRI real
DA3 IRI Real40
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• Occultation event distribution during the
  selected day (2009.266). Also shown is the
  co-located Ionosondes and profile number(22
  stations, 72 profiles in total)

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Results1

• An example of DA retrieval of simulated TEC by
  three different backgrounds

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Results2

• Comparison of NmF2 hmF2 of 3 DA retrievals
  from simulated TEC

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Results3

• Comparison of all Ne and error statistical of
  Abel retrieval and DA2 retrieval from simulated
  TEC

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Validation1

• Comparison of EDP retrieved by Abel and DA method
  between two co-located cases in the same time.

data assimilation retrieval is less influenced
than Abel method by the ionospheric inhomogeneity
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Validation2 (Simulation)

• Comparison of the latitude and altitude Ne and
  its retrieval error from simulation
• LT13
• Manmade plasma cave disappears in DA retrieval.

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Cont.(real data)

• Comparison of Ne retrieved from real data by Abel
  and DALT13

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Validation3(Simulation)

• Comparison of Ne and its error from simulation

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Cont.(real data)

• LT-MLat variation of Ne from real data

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Validation4 (With Ionosonde)

• An example of retrieved EDPs in comparison with
  co-located Ionosonde EDP

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Cont.

• Statistical comparison with co-located Ionosonde
  data (below hmF2 Ne)

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Conclusion

• Data assimilation Retrieval has a better
  performance than Abel retrieval from simulation
  study
• DA method can improve the retrieval especially
  around and below F2 peak region.
• The climate features such as manmade plasma cave
  (also call 3 E layer peaks) are improved by Data
  assimilation retrieval.
• Comparison with Ionosonde data confirms the
  validation of DA retrieval methond.

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• Data assimilation retrieval can improve the
  retrieval by both the simulation and real data
  test, but it has following disadvantages
• 1, Big computation.
• 2,Include the model information.
• 3, If the relative TEC (which is very accurate)
  is assimilated, it assumes the background model
  is unbiased, which is not usually satisfied.
• 4, If the absolute TEC is assimilated, the
  uncertainty of the absolute TEC calculation will
  influence the retrieval quality.
• 5, Might have degraded performance during
  disturbed condition.

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World Map by COSMIC, for fun