Retrieval of Dynamical Ionospheric Parameters through High-Latitude and Geosynchronous FUV Imaging T...
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Transcript of Retrieval of Dynamical Ionospheric Parameters through High-Latitude and Geosynchronous FUV Imaging T...
Retrieval of Dynamical Ionospheric Parameters through High-Latitude and Geosynchronous
FUV Imaging
T J Immel, S L England, S-H Park Space Sciences Laboratory, University of California Berkeley
R Eastes Florida Space Institute, University of Central Florida
W McClintock Laboratory for Atmospheric and Space Physics, University of Colorado
R Daniell Ionospheric Physics dot com
Highly Inclined LEO Orbit
Fixed/slowly precessing Local Time.
~25º longitudinal separation of passes.
24 hours to obtain full longitudinal coverage.
Locations on Earth imaged exactly once per day.
Polar HEO Orbit
1º per day change in Local Time.
180º longitudinal separation of passes.
Instantaneous coverage of a large range of longitudes, local times.
5-7 hours of dwell time on particular local times.
Drift Speed Determination Challenges
Fairly low per pixel counting rates (2-6 cts/pixel/image)
Keograms method co-adds pixels in 0-25º magnetic latitude range, ignoring lat/height velocity shear.
By-hand determination of bubble location suffers from subjectivity, is time-intensive.
Least-squares fit (linear through cubic based on CHISQ test of all fits) to bubble longitude vs. time presumes regular drifts.
New Drift Speed Determination Approach
Treatment of all FUV data in separate 1/2º latitude bins.
Keograms method used, but cross-correlations are used to determine location of bubble in successive images.
Individual bubbles identified by comparison of results of tracking attempts in each latitude bin.
Instantaneous velocities determined in sliding 1/2 hour window.
TOAD: TTracking OOf AAirglow DDepletions
Latitudinal shear is implicitly determined
Non-subjective determination of speed
2 x number of bubbles tracked by TOM
Exhaustive, CPU hungry search
New Drift Speed Determination Approach
Treatment of all FUV data in separate 1/2º latitude bins.
Keograms method used, but cross-correlations are used to determine location of bubble in successive images.
Individual bubbles identified by comparison of results of tracking attempts in each latitude bin.
Instantaneous velocities determined in sliding 1/2 hour window.
TOAD in action, 12-12.5º latitude bin
1) Brightness variation vs. LT is normalized.
2) 2.5 degree longitude smoothing function applied.
3) High-pass filter is applied.
After initial processing, eastward drifting forms are clearly visible. Tracking of depletions can begin.
TOAD in action, 12-12.5º latitude bin
1) Three UTs are picked to provide 10º wide samples for cross-correlation with neighboring UTs.
2) Tracks are saved for each latitude bin and compared with neighboring latitudes for identification of bubbles.
TOAD in action
With the application of a fill algorithm, 5 bubbles are automatically identified
1) Three UTs are picked to provide 10º wide samples for cross-correlation with neighboring UTs.
2) Tracks are saved for each latitude bin and compared with neighboring latitudes for identification of bubbles.
TOAD vs. TOMVelocities in EIA now lower
than Jicamarca (0º Lat)Latitude/Altitude Shear now
clearly measured
Previously identified longitude dependence in drift has latitude component as well. (!?!)
TOAD has a Future
GOLD (RBSP/MO) will offer an excellent opportunity for the observation and tracking of ionospheric bubbles in the low-latitude ionosphere.
Simulations show that TOAD would retrieve drift speeds with high confidence at ± 25º Magnetic Latitude
ConclusionA new automated technique for tracking large-scale irregularities in the low latitude ionosphere offers significant improvements over earlier techniques that are both time-consuming and subjective.
These techniques can be applied to ANY space-based imaging database that has significant dwell time at low latitude, including polar HEO, geosynchronous, and any orbit in-between.