Formosat3 / COSMIC The Ionosphere as Signal and Noise
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Formosat3 / COSMICThe Ionosphere as Signal and Noise
Christian Rocken, Bill Schreiner, Sergey Sokolovskiy, Doug Hunt, Stig Syndergard
UCAR COSMIC Project
FORMOSAT-3
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Status of Constellation April 23, 2008
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Radio Occultation
Ionosphere as signal
Ionosphere is noise
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Over 1 Million Profiles 4/21/06-4/15/08
Neutral Atmosphere Ionosphere
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Ionospheric CalibrationWe estimate systematic ionospheric error by computing the “mean of the iono-free bending angle minus neutral bending angle (from climatology) in the 60-80 km height bin”.
We compare this quantity “smean” for daytime vs. nighttime soundings.
COSMIC Days 0-120, 2007
-20 < Lat. < 20
DAY (11<LT<15) smean= -1.19 e-7 rad
NIGHT (2<LT<6) smean=-0.37e-7 rad
We can see the day vs. night iono bias change we expect that we can monitor the change of this bias to better than 0.5e-7 rad during the 11-year solar cycle.
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Relationship of F10.7 / Bending Bias/ Temperature
F10.7
BA Bias
The bending angle change of +3 e-7 rad due to change in solar activity would cause a apparent stratospheric warming of:
0.6 / 0.4 / 0.2 deg K at 30 / 25 / 20 km.
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Ionosphere as “Noise” Summary In RO the ionosphere is corrected by forming the “standard” dual
frequency linear combination of L1 and L2 bending angles This correction does not completely eliminate the ionospheric
effect– Significant random noise remains which can affect profiles for weather
forecasting down to 25 km altitude – The residual ionosphere also introduces a bias, which - if left uncorrected -
could introduce a significant spurious “warming with decreasing solar activity” signal at 30 km in the stratosphere of ~ 0.6 deg K with the 11 year solar cycle.
Methods have been developed to minimize the “ionosphere as noise” so that it becomes largely insignificant below 25 km.
At altitudes 25-40 km the ionosphere remains the most significant noise source for RO
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COSMIC trans-ionospheric radio links for a 100-min period, June 29, 2007
Amount of COSMIC-observed Trans Ionospheric TEC Data
Quality of abs. TEC ~2 TECU
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Current Latency of COSMIC TEC Data
Location of Low-Latency TEC Arcs
Most data are downloaded from Satellites < 100 mProcessing at CDAAC takes ~ 20 minutes
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Comparisons with ground-based data
Courtesy of Jiuhou Lei
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COSMIC - Ionosonde ComparisonJan. 2008, distance < 500 km, time difference < 15 min, colors indicate ionosondes
HMF2rms=57 km
F0F2rms=0.60 MHz
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Scintillation Sensing with COSMIC
No scintillationS4=0.005
ScintillationS4=0.113
GPS/MET SNR data
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Amplitude scintillations (S4 index based on 50-Hz observations)
E-Layer scintillation:
Occurs at all local times except near sun-rise (3-7 LT), strongest near sun-set (14-19 LT).
Most active between 20-60 deg north and south latitude
More pronounced in NH than SH
Stronger S4 than F-layer scintillation
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F-Layer scintillation:
Occurs sunset to sunrise (19 - 5 LT).
Most active in equatorial region (+/- 30 degrees).
Weaker S4 than E-layer scintillation
Amplitude scintillations (S4 index based on 50-Hz observations)
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What comes after COSMIC? Several Options for a follow - on mission are discussed and
considered by US agencies– Participation in a Taiwan 6+ satellite follow on mission (2012)– Iridium has proposed to use (some of) its 64 future communication satellites
as a platform for RO observations (2013 ?) – CICERO plans to launch 24 satellites (starting in 2011) and to sell data
Planned improvements compared to COSMIC – Plan for lower data latency. Goal of 10-15 minutes (more ground stations,
or real-time satellite to satellite downlink) – Observations of GPS and Galileo (Glonass?, Compass?)– More TEC arcs and soundings
Community feedback on requirements and secondary space weather payloads for future mission should be provided to UCAR
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Summary In the 2 years since launch COSMIC has generated and distributed
over 1.3 million ionospheric profiles and TEC arcs COSMIC is now also generating a large amount of scintillation
observations COSMIC ionospheric observations are of high quality and most
products are available within < 120 minutes of on-orbit collection, some within < 30 minutes
All data are available from www.ucar.cosmic.edu Follow on missions for COSMIC are now in planning stages and
input from the space weather community is needed
UCAR COSMIC program is presently looking for a scientist to take charge of our ionospheric processing
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