6/21/10 ionospheric mitigation schemes and their consequences for biomass product quality o. french...

6/21/10

Ionospheric mitigation schemes and their consequences for BIOMASS product quality

O. French & S. Quegan, University of Sheffield, UK

J. Chen, Beihang University, China

ESA, Holland, 4th March 2010

Task 100: Database of Ionospheric Scenarios

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Overview

1. Limitations of initial strategy2. Modified strategy3. Deliverables

a. database;b. simulation codes;c. technical note 1;

4. Technical issues and scope of software5. Further work6. Effect of orbit local time upon ionospheric scintillation7. Relation of TEC fluctuations to FR8. Use of GPS TEC database

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Limitations of Initial Strategy

• Original proposed approach was to generate database of ionospheric phase screens

• Limitations:a. Computationally onerousb. Large data storage requirementsc. Inflexibled. Redundancye. Can only be performed at UoS

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Modified Strategy

• To generate a database of the WBMOD output• To provide codes that can run simulations using the above database

• Advantages over previous methodologya. More flexibleb. Reduced data storage requirementsc. Time savingsd. Reduced redundancye. ESA can run on site

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Deliverables: Database

• Database entries for the following scenarios:

Parameter Values contained within database Parameter type

Satellite altitude (km) 650 Satellite

Antenna length (m) 20.16 SatelliteOrital inclination (°) 98 SatelliteFrequency (MHz) 435 SatelliteOrbital node type dawn dusk SatelliteLook angle (°) +30 (night) -30 (day) SatellitePlanetary index, Kp 1.0 3.0 7.0 IonosphereCk confidence interval (%) 99.0 Ionosphere

Date 1995 - 2005 inclusive at 10 day intervals

Temporal

Satellite latitude (°) -80 to 80 inclusive SpatialSatellite longitude (°) -180 to 180 inclusive Spatial

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Deliverables: Database

• Each entry comprises the WBMOD output for:a. Satellite locations between ±80°N at 1° resolution in

latitude and longitude.b. Fixed equatorial local time throughout a single datec. A specific set of ionospheric and satellite parameters

• See Technical note 1 for full list and definitions of WBMOD parameters.

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Gro

und

Latit

ude

Ground Longitude

log1

0 {C

kL}

Global map for 99th percentile of log10 CkL

Night-looking dawn node on 1/1/1995 and Kp = 1

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Deliverables: Simulation codes

• Runs simulations of ionospheric phase screens for a particular scenario:

a. Locationb. Timec. Ionospheric conditionsd. Orbit configuration

• Codes draw the WBMOD data required for a given simulation from the database.

• See Technical note 1 for full description of simulation codes and their operation.

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Data outputs: • 2D phase screens • Range autocorrelation• Azimuth autocorrelation• 1D phase slices• Point spread functions• Metrics• Statistics

Phase screen geometry:

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Deliverables: Simulation codesLy

(k

m)

Lx (km)

Phase deviation

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Phas

e de

viati

on (r

ad)

Azimuth (km) Azimuth (m)

Nor

mal

ised

PSF

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Scope of codes

Run Times• On the University of Sheffield servers, 100 phase slice realisations for a given scenario takes approx. 30 minutes.• This can vary depending on the number of 1D phase slices extracted from each

Limitations• Memory constrains maximum side length of square phase screen to be twice synthetic aperture

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Further Work

Simulation of 1D phase screen• Length of simulation extended at expense of full 2D correlations (ongoing)

Full study of 2D correlation• 2D autocorrelation function given by Rino 1979• Can be calculated from WBMOD output• Extent of decorrelation will dictate retrieval algorithms

Click to edit Master subtitle style

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Effect of orbit local time

Locations covered:• Boreal (BO): Sweden• Temperate (TE): Austria• Equatorial (EQ): Borneo


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Orbital parameters used:• Altitude = 650km;• Inclination = 98°;• Look angle = 30° (night looking);• Frequency = 435 MHz;• Antenna length = 20.16m (Concept 2 of BIOMASS

RfA).

Ionospheric conditions:• date = 21/6/2000, close to solar maximum;• KP = 3 (electron precipitation boundary at

61.2°MagN);• log10CkL percentile = 99%;


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Satellite node is defined by its local time (LT) as it passes the equator

Orbital nodes considered:o Dawn ascending

• 05:00• 06:00• 07:00

o Dusk descending• 17:00• 18:00• 19:00

Away from equator LT deviates from its equatorial value


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Local Time

18:00

18:00

06:00

Later Later


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Boreal location: Sweden (17°E, 65°N)

• High disruption for all nodes; CkL ≈ 1033• Little variation with orbit local time

Ly

(km

)

Lx (km)

One-way phase deviation f

Azimuth distance (m)

Point spread function

06:00


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Equatorial location: Borneo (115°E, -2°N)

Little disruption to PSF for all dawn nodes, and 17:00 and 18:00 nodes. CkL ≈ 1031

Ly

(km

)

Lx (k m)

One-way phase deviation

Point spread

function


18:00


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Large disturbance for 19:00 node • post-dusk region → high fluctuations, CkL ≈ 3.6 x

1035

Ly

(km

)

Lx (km)

One-way phase deviation


Point spread function

19:00


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Satellite is night looking – looking into the region of high ionospheric fluctuation

Effect disappears for the 19:00 orbit when day looking configuration is used

• Looking away from region of high fluctuation

Temperate location: Austria (12.5°E, 47°N)

• Little disruption for all nodes; CkL ≈ 1031• Little variation with orbit local time


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Summary

General trends as LT moves from night to day:• Increase in mean TEC and FR;• Decrease in ionospheric fluctuations (CkL).

Post sunset equatorial zone:• Pronounced increase in CkL for 19:00 night-looking

node• Can be avoided by using day-looking setup

Boreal zone is a problem under all circumstances.


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TEC fluctutations & FR

Phase fluctuation, φ (rad), is related to TEC (TECU) via

and FR, Ω (rad) to TEC by [1]

Therefore

[1] Belcher, D.P. Theoretical limits on SAR imposed by the ionosphere, IET Radar Sonar Navig., 2, 435-448 (2008)


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TEC fluctutations & FR

For BIOMASS, f = 435 MHz and this reduces to

and for Bm = 3.5 x 10-5 T

Meaning that a phase fluctuation of at least 445° is required to achieve a fluctuation of 1° in FR.

Is this beyond measurement capabilities?


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Use of GPS data

Various sources of GPS TEC data:• Centre for Orbital Determination in Europe (CODE) http://www.aiub.unibe.ch/content/research/gnss/code___research/index_eng.html• International IGSS Service (IGS) - includes CODE http://igscb.jpl.nasa.gov/

Longitude• -180° to 180° E• 5° resolution

Latitude• -87.5° to 87.5° N• 2.5° resolution

Time• From 1992

onwards• 2 hours

resolution


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Use of GPS data

Centre for Orbital Determination Europe (CODE) data• Accuracy of ±3.5 TECU

Thorough statistical analysis ongoing

6/21/10 ionospheric mitigation schemes and their consequences for biomass product quality o. french...

Documents

database database entries

d phase slices

database advantages

given simulation

ionospheric scintillation7

wbmod data

length of square phase

d autocorrelation function