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The Ionosphere and its Impact on Communications and Navigation
Tim Fuller-RowellNOAA Space Environment Center and
CIRES, University of Colorado
Customers for Ionospheric Information
High Frequency (HF) Communication (3-30MHz) ground-to-ground or air-to-ground communication establish accurate maximum useable frequencies support automatic link establishment systems
e.g., civilian aviation, maritime, frequency managers
Single Frequency GPS Positioning and Navigation single frequency potential sub-meter accuracy positioning
e.g., civil aviation, advanced vehicle tracking, potential for E911improvements
Dual Frequency GPS Positioning and Navigation decimeter accuracy 10-50 cm
e.g., real-time kinematic (RTK), autonomous transportation, off-shoredrilling and exploration
rapid centimeter accuracy positioning 1-2 cm e.g., surveyors, possible InSAR (land radar) applications
Customers for Ionospheric Information Satellite Communication
specification and forecast of scintillation activity e.g., satellite operators, drilling companies
Situational Awareness Depressed maximum useable frequencies
Steep horizontal gradients
Unusual propagation paths
Larger positioning errors
High probability of loss of radio signals
The Thermosphere and Ionosphere
Electron Density Profile
Vertical profile of electron density from GPS/MET comparedwith Millstone Hill incoherent scatter radar observations
0
1 0 0
2 0 0
400
5 0 0
6 0 0
7 0 0
1.0E+
3
1.0E+
4
1.0E+
5
1.0E+
6
Altit
ude (
km)
E le c tro n D e n s ity ( 1 /cm ^3 )
M ills t o n e ( P L = 4 4 8 ) , 4 2 . 6 N , 7 1 . 5 W , 1 3 : 2 8 : 0 0 U T C
G P S / M E T , # 0 0 0 3 , 4 6 . 9 N , 5 7 . 5 W , 1 3 : 2 9 : 3 2 U T C
P IM ( @ # 0 0 0 3 )
300
Courtesy:Chris Rocken
NCAR
Solar Flares
Coronal Mass Ejections
Solar Proton Events
Solar Flares Increased X-ray fluxD-region ionization
Arrival time: 8 minutesDuration: 1-2 hours
Effects:HF absorptionDisruption of low frequencynavigationGPS navigation
Users: mariners, coast guard,HF frequency managers,commercial aviation, military
Solar Proton EventsHigh energy particles
Arrival time: 15 mins to few hoursDuration: several days
Effects:Single event upsets (SEU)Deep dielectric chargingHF absorptionLow frequency navigation outageRadiation hazard
Users: satellite operators, HFfrequency managers, commercialaviation, mariners, astronauts, ..
Coronal Mass EjectionsGeomagnetic Storm
Arrival time: 1-3 daysDuration: 1-2 days
Effects:Spacecraft chargingSatellite dragHF CommunicationsGPS NavigationInduced currents
Users: Power companies,satellite operators, HF frequencymanagers, FAA, military, GPS,...
Effect of Solar X-rays on D-Region and HF Propagation.
D-Region Absorption Product based on GOES X-Ray Flux (SEC Product) The map shows regions affected by the increased D-region ionization resulting
from enhanced x-ray flux during magnitude X-1 Flare
Solar X-raysGOES
Dayside responseZenith angle dependenceTime scale follows source
SHORTWAVEFADE (SWF)
00 241812
MAXIMUMUSEABLEFREQUENCY
LOWESTUSEABLEFREQUENCY
X-RAY EVENT
06
TIME
FR
EQ
UE
NC
Y(M
Hz)
0
5
10
15
USEABLEFREQUENCYWINDOW
Solar Flares:HF AbsorptionRadio Blackout
Radio Wave PropagationFort Collins, CO to Cedar Rapids, ID
Signal Strengthat 10 MHz
00 241812060
5
10
15dusk dawn
night day
Radio Wave PropagationFort Collins, CO to Cedar Rapids, ID
Signal Strengthat 10 MHz
00 241812060
5
10
15dusk dawn
Flare
TEC GPS Differential Phase measurements
Equatorial African station, near noon
X17
Solar Protons
PCA depends on solar illuminationO2 - e- attachment process in the D-region
Combined X-ray and PCA
Coronal Mass Ejection
A single eruption can release a billion tons ofmaterial into the solar windSpeeds can exceed several million miles perhourEnergetic particles accelerated by shocks cause bright flashes inthe image (andin DNA!)
Increased energy input to the upperatmosphere: auroral particleprecipitation and magnetosphericconvection electric field
Epc 10 - 300 kV in minutes
Large temperature and circulation changesin the upper atmosphere
Oxygen Depletions Imaged from Space
wipe out ionosphere
Strong correlation betweenO/N2 and ionospheric
depletions
STORM product
The geomagnetic storm onMonday August 18th 2003wiped out the normaldaytime peak in TEC andelectron density over NorthAmerica
Normal quiet-day maximumon August 17th
Ionospheric depletion onthe 18th during the storm
Ionospheric TEC using data assimilation techniques
Electrodynamics
Penetration and dynamoelectric fields can strengthenthe EIA and deepen equatorialholes.
Ring current polarizationelectric fields can transportionospheric plasma andproduce troughs
Huge gradients in plasmadensity ensue.
CHAMP (400 km) OSEC: HalloweenMannucci et al. 2005
One of the challenges:
October 29th, 2003stationary walls of TECcompromise integrity of
LAAS
TEC walls:130 TEC units over 50 km
20 m of GPS delay;walls move 100 to 500 m/s
SED?wall
Courtesy: Tom Dehel, FAA
Steep TEC gradients increaseGPS positioning errors
5m
High correlation betweendisruption of WAASavailability and TEC gradients
The Kalman Filter andextracting information
Primary Product: Vertical TECReal-time ionospheric maps of total electron
content every 15 minutes
Slant-Path TEC Maps2-D maps of of slant path TEC over the CONUSfor each GPS satellite in view updated every 15minutes
Applications:1. Ionospheric correction for single frequency GPS and NDGPS positioning2. Dual-frequency integer ambiguity resolution for rapid centimeter accuracypositioning
Sat. 1
Sat. 5
Sat. 14
Sat. 29
.etc
A
A
A
A B
B
B
B
C
C
C
C
C
Scintillations
Distribution of high scintillation events
Courtesy:Paul Straus
Aerospace Corporation
and Maps
Signal-to-noise ratio
Electron Density [log/m3]
Storm
Quiet
4.4LT
Basu et al. 2001
Bite-outs
HeavyFluid
LightFluid
Ionosphere
Steep bottomside densitygradient during / after sunset
Fluid instability analog(Rayleigh-Taylor instability)
ScintillationsHeavyFluid
LightFluid
Plasma Bubbles
WBMOD: empirical model
physicalmodeling
GUVI Nighttime FUV IonosphereObservations
I = ne2 dse + O+ O* (135 nm)
Longitude
Latit
ude
Depleted Flux Tubes
App
leto
n A
nom
aly
Magnetic Equator
CourtesyAPL
Motivation: Planetary wave periodicities in daysideionosphere? H inferred Drifts using a Neural Network algorithm between March 13 (73) and April 14 (105), 2004
-30
-20
-10
0
10
20
30
40
50
0 4 8 12 16 20 24
Local Time (hours)
Dri
fts
(m/s
)
DOY = 73DOY = 74
DOY = 75
DOY = 76
DOY = 77DOY = 78
DOY = 79
DOY = 80DOY = 81
DOY = 82
DOY = 83DOY = 84
DOY = 85
DOY = 86DOY = 87
DOY = 88
DOY = 89
DOY = 90DOY = 91
DOY = 92
DOY = 93DOY = 94
DOY = 95
DOY = 96DOY = 97
DOY = 98
DOY = 99DOY = 100
DOY = 101
DOY = 102DOY = 103
DOY = 104
DOY = 105
Avg.Avg._IFM
Dayside electrodynamics during 2001
Possible PW signaturesElectrodynamics drives plasma transport
Courtesy D. Anderson & A. Anghel (2006)
Mid-latitude day-to-day variability inionospheric total electron content
El Nio
GW
PW
Tides
QBOSA
O
Electrodynamics
Scintillations
Ionospheric Bubbles
Courtesy of Rashid Akmaev
Tidal signatures in nightside EquatorialIonospheric Anomaly
IMAGE composite of 135.6-nm O airglow (350-400 km) for March-April 2002 andmagnitude of tidal temperature oscillations at 115 km (Immel et al., 2006).
Many of the space weather effectson communication and navigationare a consequence of the responseof the upper atmosphere to solarflares, coronal mass ejections, andsolar proton events
Day-to-day variability can alsoarise from the connectionsbetween terrestrial and spaceweather
Conclusion