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.

Tracking ionospheric bubbles in the EIA

Tracking ionospheric bubbles in the EIA

Tracking ionospheric bubbles in the EIA

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.