1. Satellite Based Augmentation Systems Brazilian Ionosphere Group Training at Stanford University October 27-30, 2003

2. MODULE 1: CONUS VERSUS GLOBAL IONOSPHERE Part A: Midlatitudes

3. CONUS VERSUS GLOBAL IONOSPHERE Part A An introduction to the ionosphere Understanding ionospheric basics so that the concerned ionospheric phenomena can be understood Creation of the ionosphere, and the effects of solar zenith angle and ionospheric dynamics This module covers: Why?Topics

4. Introduction to the Ionosphere Introduction to the ionosphere  Upper atmosphere  Ion and electron production due to photoionization and particle precipitation  Chemical loss  Ionospheric dynamics under the control of the intrinsic geomagnetic field References  Introduction to Ionospheric Physics [Rishbeth and Garriott, 1969]  Geophysical Handbook [Air Force Research Laboratory, …]  The Earth’s Ionosphere [Kelley, 1989]  Ionospheres [Schunk 2000]

5. Earth’s Upper Atmosphere

6. Photoionization Photon from the Sun O+O+ e-e- O atomic (or molecular) gas electronion h oxygen Examples of Dissociative Ionozation Examples of Photoionozation Ionization Threshold Energies

7. Production Normalized Chapman production function versus reduced height z, parametric in solar zenith angle . [Rishbeth and Garriot, 1969] h 0 : reference height Optical Depth Chapman Production Function

8. Layers of Ionization Electron production profiles by solar irradiances at the EUV band Radiation at different wavelengths contributes to the creation of E - and F -layers For SSN = 60 –X(E), 8 – 140 Å –UV(E), 796 – 1027 Å –E = UV(E) + X(E) –F, 140 – 796 Å –E+F, 8 – 1027 Å

9. Ionization due to Aurora Precipitation Computed ionization rates for O +, O 2 +, and N 2 +, respectively, due to precipitating charged particles at various energy levels

10. Loss of Ions and Electrons Charge Exchange Radiative Recombination (slow) k f /k r  1.13 Airglow Emission (red line) k ~ 10 -12 (250/T e ) 0.7 K ~ 10 -7 (300/T e ) 0.5 Dissociative Recombination (k ~ 10 -10 )

11. Ionospheric Dynamics - C Ionospheric plasma motions under the control of the geomagnetic field – ExB drift – Neutral wind drag – Diffusion – Collision vs. gyro-rotation  Collision frequency  Gyro-frequency – F-region and E-region

12. Ionospheric Dynamics Dynamo Electric Fields Vertical Drift Zonal Drift

13. High Latitude Plasma Convection Electric Potential

14. Plasma E  B Drift Motions of electron and ion under an external electric field ( E ) –In the same or opposite direction of E Gyro-rotation –The direction of motion of a charged particle is under control of magnetic field ( B ) so that the particle gyro-rotates around the B field Motions under both E and B fields –Both electrons and ions move in the E  B direction In the ionosphere, ion-neutral (mostly) and electron-neutral collisions also affect motions of charged particles The effects due to the collisions compete with gyro-rotations, and the superior determines the motion directions Gyro-frequencies: At 180 km:  i (O+) ~ 220 Hz, in ~ 10 Hz

15. Ionospheric Dynamics - B Thermospheric wind – Tidal forces: solar heating – HWM model  Um and Uz in 2-D  Um and Uz in 1-D

16. Plasma Motions Controlled by B-Field In regions where  >> in ( F region), plasma move in directions either perpendicular to magnetic field B (in the E  B direction) driven by electric field E, or parallel to B driven by horizontal wind v n (gradient of pressure  p i is not included) B vnvn v i, ∥ v i,up I

17. Dynamical Effects Plasma move into different regions where the lifetime of the plasma changes due to the altitude-dependent chemical loss processes As the plasma move into a different region, dominant effects change –Example: F -layer rises, plasma on the bottom side leave from a chemical-dominant region and enter a region where diffusion dominates

18. Fluid Dynamic Equations for the Ionosphere Mass and Momentum Conservation

19. Ionization, chemical loss, and dynamics

20. Neutral, Ion, and Electron Densities Middle Latitudes

21. Seasonal Variations at Mid-Latitudes

22. Seasonal Variations at Low-Latitudes

23. 11 Year Solar Cycle Solar activity caries from minimum to maximum with a 11-year cycle During years of high sun-spot number years, solar radiation enhances at most of its spectrum, including solar flares and coronal mass ejections Increased solar activities directly affect ionospheric densities through photoionization and coupling of magnetosphere, ionosphere, and thermosphere, which gives rise to ionospheric disturbances

24. Global Ionosphere

25. CONUS VERSUS GLOBAL IONOSPHERE Part B The mid-latitude ionosphere and storms Context for understanding ionospheric algorithms applied to WAAS Understand why low-latitude algorithms will differ from WAAS algorithms Ionospheric structure and behavior over US Quiet versus storm-time behavior at mid- latitudes This module covers: Why?Topics

26. Electron Density Profiles at Mid-Latitudes Altitude profiles of the ion composition and n e measured using incoherent scatter radar at Arecibo Daytime: top panel Nighttime: bottom panel Peak at ~300 km

27. n e Diurnal and Latitudinal Variations n e profiles versus UT measured using incoherent scatter radar at Arecibo (Puteor Rico, LT = UT – 4 hrs) and Millstone Hill (Massachusetts: LT = UT – 4.7 hrs) Diurnal variations Peak at ~300 km Maximum in the afternoon at ~ 2 LT Minimum at dawn at ~5 LT Latitudinal variations

28. TEC in CONUS: Nominal Conditions A snapshot of TEC derived from GPS dual-frequency observations using a ground- based GPS receiver network under nominal ionospheric conditions Small TEC spatial gradient allows a planar fit to represent its nominal behavior

29. TEC in CONUS: Storm Conditions Under storm conditions, large gradient in ionospheric density and TEC can occur in the CONUS region Storm-time ionosphere may not be well represented by a planar fit A threat model must developed to provide warning and realistic error bound must be provided to WAAS to protect the system from the increased errors

30. Corona Mass Ejection Above: Helical structure in a CME observed with LASCO on June 2, 1998. Right: The August 11, 1999, eclipse.

31. Sun-Earth Connection and Living With a Star Interacting Magnetic fields, plasma, energetic particles Ionosphere and Atmosphere Varying Radiation, Energetic particles Solar wind

33. Magnetosphere-Ionosphere Coupling

34. Geomagnetic Storms During April 2002

35. Storm Effects Charged particle precipitation in the auroral zone Significant enhanced plasma convection at high latitudes Penetration of electric fields into middle and low latitudes –Steepened mid-latitude ionospheric trough –Storm-time Enhanced Density (SED) –Ionospheric Undulation and irregularities at subauroral latitudes –Enhanced equatorial anomaly –Triggering of equatorial “bubbles” or irregularities and causing scintillation Auroral electron jet –Joule heating and friction heating Heating in the high-latitude thermosphere –Traveling ionospheric disturbances (TID): positive storm effects –Enhanced equatorward wind  Positive storm effects  Possibly suppressing equatorial irregularities –Global thermospheric circulation change –Thermospheric composition change: negative storm effects Erosion of the plasmasphere

36. SED

37. Storm Effects

38. Negative Storm Effects

39. Positive and Negative Storm Effects Storm-time positive and negative TEC changes as well as large TEC gradient at mid-latitudes present a great challenge to WAAS

40. Mid-Latitude Irregularities during a Storm

41. MODULE 1: CONUS VERSUS GLOBAL IONOSPHERE Part B: Low Latitudes

42. CONUS VERSUS GLOBAL IONOSPHERE, Part B The low latitude ionosphere Understand why low-latitude SBAS is challenging The Equatorial Ionization Anomaly (EIA) Local time behavior of the EIA Plasma depletions (bubbles) Scintillation Storm versus quiet time behavior This module covers: Why?Topics

43. [Placeholders] Global TEC map pointing out equatorial feature Overlay geomag equator if possible Classic picture of EIA formation with arrows TOPEX plot showing anomaly Statistics relative to planar fit Picture of E with pre-reversal enhancement Post-sunset plasma instability Picture of depletion size/scale TEC plots of depletions –– Dehel Depletions and scintillation Plot of amplitude scintillation Some statistics of scintillation Attila storm versus quiet statistics Summary

44. Equatorial Ionization Anomaly (EIA)

45. TOPEX Altimeter TOPEX/Poseidon satellite carries a dual-frequency radar measuring the height of sea level Ionospheric vertical TEC is derived from the differential delay of the signals Vertical TEC is measured above oceans at mid- and low-latitudes for many years

46. Equatorial Anomaly Shown in TEC Low latitude ionospheric structures under nominal conditions Large gradient and curvature: Equatorial anomaly

47. Dynamical Effects at Low-Latitudes

48. Dynamical Processes in the Equatorial Ionosphere

49. Ionospheric Plasma Vertical Drift In the Equatorial Region Averaged patterns of vertical plasma drift in the equatorial region Plasma move upward during daytime and downward at nighttime A pre-reversal enhancement occurs around dusk

50. Equatorial Anomaly Shown in n e Calculated electron contours (log 10 n e ) as a function of altitude and latitude at 2015 LT for equinox conditions

51. Equatorial Anomaly Shown in TEC EIA primarily appear in daytime and evening The peak-to-trough ratio becomes large around the dusk due to the pre-reversal enhancement in the plasma vertical drift

52. Seasonal Variations at Low-Latitudes

53. Plasma Bubbles and Plumes Electron Density and TEC Depletion Low-Latitude Ionospheric Irregularities

54. Plasma Plumes at the Equator Coherent scatter echoes recorded in a range-time-intensity map using the Jicamarca ISR Signals are backscattered by 3-meter ionospheric density irregularities

55. Fluid Rayleigh-Taylor Instability

56. n e Bubbles and Depletion at Low Latitudes Back scattered UHF ISR signal power indicates plasma irregularities The AE satellite flew through the plasma bubbles – depleted region – in the Pacific low-latitude ionosphere Bubbles and depletions shown in satellite n i profiles

57. TEC Depletion at Low Latitudes Plasma depletion or “bubbles” were captured in GPS dual-frequency phase measurements at a equatorial site in a solar maximum year Large values of the rate of TEC (ROT) and rate of TEC index (ROTI, standard deviation of ROT over a time interval), derived from the same GPS phase data, indicate ionospheric irregularities The measurements show that the irregularities are closely associated with the plasma depletion The irregularities cause scintillation in GPS signals Curtsey: FAA Plasma depletion or bubbles Random fluctuations in rate of TEC change

58. Longitudinal Extension of Plasma Bubbles Incoherent scatter radar measurements of electron densities and coherent scatter echoes due to irregularities Multiple bubbles can occur on a single night, separated by a few hundreds of kilometers in the E-W direction

59. Low-Latitude n e Depletion Shown in Airglow Emission Depleted region is elongated along the magnetic flux tubes The extension of the depleted region in the north- south direction is in the order of 10 3 of kilometers The width (in longitude direction of depleted region can be in a few hundreds of kilometers There can be multiple depletion strips in longitude dimension on a single night Depleted regions move eastward in a speed of ~100 m/s

60. Low-Latitude Magnetic Field Configuration Latitude extension between 400 and 800 km

61. Plasma R-T Instability g  gravitational acceleration L -1  gradient parameter or scale length in  ion-neutral collision frequency   F-region loss coefficient v p  plasma vertical drift Linear growth rate of plasma R-T instability

62. Rise of the F-Layer at Dusk Altitude profiles of the n e measured using ALTAIR incoherent scatter radar at Kwajalein The n e profiles were measured during evening hours and showed rise of the F - layer The F -layer peak now is at ~470 km (instead of ~300 km) The rise of the layer continues for some time

63. Electron Density Profiles at Low Latitudes Measured n e profiles at Kwajalein were used to the rise of the F -layer which approximately indicates the plasma vertical drift Top panel: ISR measurements Middle and bottom panels: ionosonde data

64. Plasma R-T Instability Growth Rate The growth rates of plasma R-T instability were computed using the ALTAIR ISR measurements of n e profiles and MSIS neutral atmospheric model

65. Ionospheric Scintillation

66. GPS Lab Tests without Scintillation March of 1999 at JPL.  t = 50-HzT = 5-min S 4 = 0.027 ~ 0.035   = 0.11 ~ 0.13 radians (1 cycle = 2  radians)

67. GPS L1 Scintillation in an Equatorial Region October 26, 2000, at Arequipa (Peru)  t = 50-HzT = 5-min S 4 = 0.18 ~ 0.45   = 0.22 ~ 0.45 radians (1 cycle = 2  radians)

68. Scintillation Morphology (Geophysical Handbook, 19xx)

69. Scintillation Indices L1-C/A L1-C/A sampled at 20-ms Detrended phase and intensity Signal-to-noise ratio 30-sec indices

70. GPS Scintillation in the Equatorial Region L1 Amplitude Phase Occurrence Rate

71. GPS Scintillation At the Equatorial Anomaly L1 Amplitude Phase Occurrence Rate

72. GPS Scintillation At High latitudes L1 Amplitude Phase Occurrence Rate

73. Simultaneous Strong Scintillation on Multiple Satellite Links Statistics of strong scintillation events observed at an equatorial anomaly site Bars show how many events were observed in which strong scintillation occurred simultaneously to multiple radio links (satellites) from a single receiver The information provides a reference to the possibility that the number of satellite links may be lost simultaneously to a receiver under scintillation conditions

74. GPS L1 Signal Power Fading Under Scintillation Conditions Recording of GPS L1 signals under ionospheric scintillation conditions has been made at low latitudes since 2000 Signal power fading and associated duration are obtained by processing the L1 amplitude data The deepest fading from an equatorial anomaly region (Santiago) reaches ~ -30 dB Power fading at -10 dB can last longer than 1 second Such data sets are a useful reference to innovative design of GPS receivers

75. Effects of Scintillation on GPS Strong amplitude and phase scintillations were measured at an equatorial anomaly site S 4,  , and ROTI characterize the scintillation activity The receiver lost lost at least L2 tracking of certain number of satellites Positioning using phase data is affected

76. MODULE 2: IONOSPHERE ESTIMATION USING GPS Part A: Measurements

77. IONOSPHERE ESTIMATION USING GPS, Part A Using GPS signals to measure the ionosphere Understand purpose and operation of SBAS reference stations Understand how ionospheric corrections are formed Forming ionospheric measurements from GPS observables Data quality and editing Calibration of GPS data This module covers: Why?Topics

78. [Placeholders] Material from Attila presentation on supertruth – leveling, editing, etc. Some plots of supertruth-based data for three levels Something showing phase vs range How biases are removed Leads naturally to GIM GIM algorithm and plots

79. MODULE 3: IONOSPHERIC THREAT MODEL

80. Design of a “threat model” for the ionosphere The threat model is used to prove the system is safe under all conditions, including when the ionosphere is disturbed Deals with the critical issue of “undersampling” The spatial threat model – augmenting GIVE because the ionosphere is not always nominal, and reference station sampling is limited Temporal threat model – augmenting GIVE due to ionospheric variability between transmitted updates This module covers: Why?Topics

81. [Placeholders] See Larry’s material Defer depletion discussion to Module 4

82. MODULE 4: RECENT WORK ON THE EQUATORIAL IONOSPHERE

83. Recent algorithm development and research needed to deploy a low-latitude SBAS New algorithms are needed for vertical guidance in a low-latitude SBAS New standards (EGOPS) must be proposed Low-latitude data sets New algorithms for estimating user ionospheric corrections Current understanding of plasma depletions and expected impact This module covers: Why?Topics

84. [Placeholders] Review issue of equatorial spatial gradients Show planar fit residuals, a map and other information (e.g. Raytheon?) that demonstrates low-latitude challenges Show some GIVE or vertical guidance numbers Review challenges associated with applying thin-shell planar fit to equatorial environment Descrive Conical domain method Review existence of plasma depletions Discuss characteristics of depletions with respect to solar cycle, local time Discuss characteristics of depletions, what is known and not known Discuss depletion characteristics: growth rates, lat/lon extent, bunching, etc. Mitigation by just setting large GIVEs, or possibly in-situ detection. USE DEHEL PRESENTATION Relationship of depletions and scintillation Recent progress on scintillation Spacing of GEOs Amplitude depth verus duration