1 J July, 2000. 1 Ionospheric Calibration for the GFO AltimeterXiaoqing Pi @ JPL Review Ionospheric...

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Ionospheric Calibration for the GFO AltimeterXiaoqing Pi @ JPL

ReviewReview

Ionospheric Calibration for the GFO AltimeterIonospheric Calibration for the GFO Altimeter

Xiaoqing PiXiaoqing Pi

Byron A. IijimaByron A. Iijima

Anthony J. MannucciAnthony J. Mannucci

Mark J. ReyesMark J. Reyes

Jet Propulsion Laboratory, California Institute of TechnologyJet Propulsion Laboratory, California Institute of Technology

July 20, 2000.July 20, 2000.

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OutlineOutline

• Objectives: Ocean altimeter calibrations • Technology: Remotely sensing the Earth’s ionosphere

using GPS• Resources: GPS satellites and the IGS global GPS

network • Methodology: Global ionospheric mapping (GIM)

• Ionospheric calibration for the GFO mission:– An automated GIM processor for GFO altimeter calibrations

– Daily deliveries of calibration data

– Accuracy assessment

• Further development

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TEC Data Sources: The IGS Global GPS NetworkTEC Data Sources: The IGS Global GPS Network

• More than 300 permanent ground GPS stations are tracking 24~27 GPS satellites around the globe (the map shows selected sites) .

• Dual-frequency (L-band) GPS observables are recorded every 30-seconds.

• GPS data are collected in near real-time (NRT, hourly) or daily through Internet and phone lines, and archived at multiple centers.

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Global Ionospheric TEC MapGlobal Ionospheric TEC Map

• Global snapshot of ionospheric TEC with a sub-hourly resolution

• Driven by GPS data collected from the global network





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Automated GIM Processor for Altimeter CalibrationsAutomated GIM Processor for Altimeter Calibrations

JPLGDHFSIOGSFCCDDISCheck data coverageSelect GPS sitesEdit dataLevel phase to pseudorange

Kalman filterGPS datafinal filter state usedas apriori for next dayTopex comparisonClimatological modelcomparison

JPLPODAACTOPEX datamapsAltimetercalibrationMakeIONEXNOAADelftERS2ephem NAVOJPLGFOephem Archiveinternallyrcv / sat biasesstats Internalweb siteHP9000/780GSFCCDDISNAVOTopexPODmapsbiasesmailstatus to ops

CDROMarchive

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GFO DeliveriesGFO Deliveries

Schedules• Daily delivery during May - August, 1999. • Daily deliveries since the middle of February, 2000.

Destinations• The Naval Oceanographic Office • NOAA

Products• Vertical TEC obtained from the GIM process along the satellite tracks.• The TEC error estimate based on the statistics of TEC difference between

GIM and TOPEX data.• A backup (to be delivered if the GIM process fails): Vertical TEC obtained

from the IRI95 empirical model.

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ValidationValidation

Error Sources

• Coarse coverage above oceans

• Slant-to-vertical mapping

• Data noise– Ionospheric irregularities and scintillation

– Receiver malfunctioning

Challenge

• Geomagnetic and ionospheric storms

Accuracy Assessment

• Comparisons between GIM and independent ionospheric measurements (such as the TOPEX TEC) as well as empirical models

• Statistical analysis to assess the accuracy of GIM over the oceans

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TEC Comparisons between TOPEX and GIM/ModelsTEC Comparisons between TOPEX and GIM/Models

Date: 01/21/2000Date: 01/21/2000

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One-Day Histogram of Difference between Models and TOPEX

0

500

1000

1500

2000

2500

-100 -90 -80 -70 -60 -50 -40 -30 -20 -10 0 10 20 30 40 50

GIM - TOPEX: RMS = 6.3 ; MEAN = -1.85IRI95 - TOPEX: RMS = 17.2; MEAN = -7.8BENT - TOPEX: RMS = 18.8; MEAN = -15.2

Number of Data

TECU (1016 el/m3)

03/21/2000

Total # of data = 4181

For 13.5 GHz signals (GFO): 1 cm = 4.5 TECU (1 TECU = 0.222 cm)

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Daily Mean Difference between Models and TOPEXDaily Mean Difference between Models and TOPEX

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20

40

60

80

100

-26 -24 -22 -20 -18 -16 -14 -12 -10 -8 -6 -4 -2 0 2 4 6 8 10

02/15/00 - 07/09/00Total # of days = 130

GIM - TOPEX

IRI95 - TOPEX

BENT - TOPEX

Number of days

TECU (1016 el/m3)

MEAN (model - TOPEX)MEAN (model - TOPEX)

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Daily RMS of Difference between Models and TOPEXDaily RMS of Difference between Models and TOPEX

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20

30

40

50

60

70

0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30

02/15/00 - 07/09/00Total # of days = 130

GIM - TOPEXIRI95 - TOPEXBENT - TOPEX

Number of data

TECU (1016 el/m3)

RMS (model - TOPEX)RMS (model - TOPEX)

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Largest Daily Positive Difference between Models and TOPEXLargest Daily Positive Difference between Models and TOPEX

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5

10

15

20

25

30

35

0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90

02/15/00 - 07/09/00Total # of days = 130

GIM - TOPEX

IRI95 - TOPEX

BENT - TOPEX

Number of data

TECU (1016 el/m3)

MAX (model - TOPEX)MAX (model - TOPEX)

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Largest Daily Negative Difference between Models and TOPEXLargest Daily Negative Difference between Models and TOPEX

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10

15

20

25

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40

-120 -110 -100 -90 -80 -70 -60 -50 -40 -30 -20 -10 0

02/15/00 - 07/09/00Total # of days = 130

GIM - TOPEXIRI95 - TOPEXBENT - TOPEX

Number of Data

TECU (1016 el/m3)

MIN (model - TOPEX)MIN (model - TOPEX)

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Further DevelopmentFurther Development

• Measurements above oceans– GPS receivers on ships?

– GPS ocean reflections

– Other types of measurements?

• Global Assimilative Ionospheric Model (GAIM)– Assimilate ionospheric data into physics-based models

– Take ionospheric dynamics into account

– Overcome data coverage problems

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Ionospheric Data AssimilationIonospheric Data Assimilation

GPS - TECGPS - TEC

DMSP - UV, Ne, NnDMSP - UV, Ne, Nn

Ionospheric MappersTEC, Ne, E, Un, ...

Ionospheric MappersTEC, Ne, E, Un, ...

Data ProcessorData Processor

Forward ModelForward Model

IonosondeNe, hmF2, (v, Un)

IonosondeNe, hmF2, (v, Un)

OptimizationOptimization

Model DriversModel Drivers

StatePrediction

Observations

Adjustment of State and Drivers

Data Selection

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