1 November 14, 2006 XPI@JPL: IWSSAR Strategy GISMO Mission Options Decadal Survey did not call for a...

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November 14, 2006 XPI@JPL: IWSSAR Strategy

GISMO Mission OptionsGISMO Mission Options

• Decadal Survey did not call for a P-Band capability

• But did open up the idea of Venture Missions costing < $200M

• First opportunity to do this is expected in Summer ‘08

• Recommend we propose providing an antenna, science team and ground system for the ESA Explorer Biomass mission and dedicating some of that mission’s timeline (in sat 2016) to acquiring GISMO data in repeat-pass mode

• Parallel development could be the Mars Science Orbiter payload

November 14, 2006 XPI@JPL: IWSSAR Strategy 2

P-band Radar Instrument Concept(for Veg. 3-D structure)

Instrument Features

Technology

• Pointing: 25° cross-track (right) of nadir• P-band (435 MHz), 6 MHz Bandwidth• Polarimetric (HH,HV,VH,VV)• 25° illumination angle• 62 km swath• 100 m resolution (20 looks)• Reflector Diameter: 9 m• Reflector Width: 7 m• Geolocation Accuracy: < 10 m• Calibration: 1 - 1.5 dB absolute, 0.5 - 1.0 relative• Noise Equivalent 0: < -30 dB

• No technology development required• Astromesh Antenna technology provides

10-15 year lifetime (TRL 9)• Phased Array Feed (TRL 6)• Heritage:

• MBSat 12-meter reflector• INMARSAT 9-meter reflector

Airborne Simulation of P-band Polarimetric Data

Phased Array FeedPhased Array Feed Stowed Reflector Support TowersStowed Reflector Support Towers

BoomBoom

Solar ArraySolar Array

9m Astromesh Reflector

9m Astromesh Reflector


Eagle Scout Mission

Radar Ground Illumination:

68 km

28 km

Illuminated Swath

Recorded Swath

Parameter Value

Imaging Geometry a) Look angle 37o (off-nadir) b) Nadir-pointing

Wavelength 63 cm Polarizations Full polarimetric capability Number of science modes 4 Spatial resolution 100 m/30 m Swath width 8 to 28 km Mass (CBE) 76.9 kg Stowed antenna dimensions 176 × 33 × 33 cm Electronics box dimensions 20 × 30 × 40 cm Power needs (ave )rage 93.3 W Data rates 0.75 to 2 Mbps Pointing accura cy requirement 0.75 o

P-Band SAR

Mission Characteristics Mission Element Characteristic

Length of Primary Mission 27 months Launch Vehicle Delta 2925 Trajectory Type Type II Launch Period 2011 Launch C3 (Max.) 17 km2/s2 Arrival Period 2011 Arrival V-infinity (Max.) 2.6 km/s Mapping Orbit Altitude 240 × 320 km Mapping Orbi t Eccentricity 0.011 Mapping Orbi t Period 112.0 min Mapping Orbi t Inclination 92.8 deg Mapping Orbi t Node Local Time 3:30-5:00 pm

Solar Array(6m x 2m)

xs

ys

FeedF

DeployableReflector

Boom

Spacecraft Bus(1.8 x 1.6 x 2.0 m)

6m

zr

3 m

0.5m

Projected Aperture

Combines Polarimetry and Repeat-pass Interferometry to characterize Martian subsurface


Eagle Scout Mission

Radar Ground Illumination:

68 km

28 km

Illuminated Swath

Recorded Swath

Parameter Value

Imaging Geometry a) Look angle 37o (off-nadir) b) Nadir-pointing

Wavelength 63 cm Polarizations Full polarimetric capability Number of science modes 4 Spatial resolution 100 m/30 m Swath width 8 to 28 km Mass (CBE) 76.9 kg Stowed antenna dimensions 176 × 33 × 33 cm Electronics box dimensions 20 × 30 × 40 cm Power needs (ave )rage 93.3 W Data rates 0.75 to 2 Mbps Pointing accura cy requirement 0.75 o

P-Band SAR

Mission Characteristics Mission Element Characteristic

Length of Primary Mission 27 months Launch Vehicle Delta 2925 Trajectory Type Type II Launch Period 2011 Launch C3 (Max.) 17 km2/s2 Arrival Period 2011 Arrival V-infinity (Max.) 2.6 km/s Mapping Orbit Altitude 240 × 320 km Mapping Orbi t Eccentricity 0.011 Mapping Orbi t Period 112.0 min Mapping Orbi t Inclination 92.8 deg Mapping Orbi t Node Local Time 3:30-5:00 pm

Solar Array(6m x 2m)

xs

ys

FeedF

DeployableReflector

Boom

Spacecraft Bus(1.8 x 1.6 x 2.0 m)

6m

zr

3 m

0.5m

Projected Aperture

Received a Category I rating in the latest Mars Scout proposal review

- possible 2013 Orbiter payload?

Combines Polarimetry and Repeat-pass Interferometry to characterize Martian subsurface

Ionospheric Weather Specifications for InSAR Ionospheric Weather Specifications for InSAR (IWSSAR)(IWSSAR)

JPL, November 14, 2006

Xiaoqing Pi

Jet Propulsion Laboratory

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OutlineOutline

• Ionospheric Effects on L-Band SAR & InSAR at dusk ─ TEC-induced near-to-far range phase ramp ( = 15~200 rad)

and suborbital Faraday rotation (5~20) ─ Ionospheric weather: TEC variations (TEC = 50 ~ 100, or

50~100%) and scintillation ( = 0.1~1 rad)

─ Effects on estimate of target displacement: 5~10 meters due to TEC, and a few 10’s cm due to scintillation (needs more studies)

• Ionospheric Weather Specifications for InSAR─ GPS-based global ionospheric data assimilation to specify 3D

electron density and TEC

─ Mapping of irregularities causing phase scintillation

─ SAR itself; GPS occultation receiver and DORIS receiver on board spacecraft to support IWSSAR

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Ionospheric EffectsIonospheric Effects

STEC1045.8

3.402

7

f

dsnfc

r

t

e

−×=

⋅= ∫r

r

πφ

dsBnf

Kr

t

e θcos02 ∫=Ωr

r

Phase or Delay:

Faraday Rotation:

ne ─ electron densityB0 ─ ambien mag. fieldθ ─ angle between k and B0

K = 2.365104 (in MKS units)

Phase & Amplitude Scintillation:

),(),(),(

),(),(),(

rrr

rrr

tAtAtA

ttt

φφφ

+=

+=

and A are random fluctuations

22

2

22

4S

φφφ −=

−=

I

II

Scintillation Statistics for Signal Intensity and Phase

( )( ) 1

5.14S

−

−

∝

∝

ff

ff

φσ

Frequency Dependence

Line-of-sight TEC

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Effects due to TECEffects due to TEC

• The quality of radar data synthesis is sensitive to the ionospheric-induced effects of (two way)

─ ∆ 90 or 1.57 rad (suborbital TEC > 0.1 TECU, L-band; 0.04 TECU, P-band) between the two ends of radar aperture (500 m ~ a few km)

─ ∆ or ∆r between near and far range can lead to 2 to 25 m target displacement in the range direction

─ 5.7 or 0.1 rad (scintillation: 0.1 ~ 1 rad, L-band )

─ Ω 10 (suborbital TEC > 20 TECU, L-band; 2.54 TECU, P-band)

• Typical suborbital daytime TEC can reach 20 to ~100 TECU

1 TECU (= 1016 electrons/m2) Corresponds to (one way)

(m) / f (GHz) (rad/) Ω ()

C-band: 0.06 / 5.00 1.69 / 96.8 0.0154

L-band: 0.24 / 1.25 6.76 / 387.6 0.25

P-band: 0.68 / 0.44 19.16 / 1097.8 1.97

The estimation of Faraday rotation (Ω) uses θ = 45 and B0 = 0.4 gauss, which in general vary with geographic location and radio geometry.

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Diurnal Variation of the IonosphereDiurnal Variation of the Ionospherethe Concern of the Concern of Dusk EffectDusk Effect

UT (tick mark = 1 hour)

TE

C

Ascension Island

1980Day to day variability at dusk – a threat to InSAR

20 TECU

Dawn

DuskMinimum at dawn – a dawn orbit to avoid ionospheric effects

P

L

Suborbital & slant path (45) are considered

FRE

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Latitudinal Variation of the IonosphereLatitudinal Variation of the IonosphereA Concern at A Concern at Low and Mid LatitudesLow and Mid Latitudes

Most of blue areas are not a concern for the Faraday rotation effect at L-band

Dawn (ascending) Dusk (descending)

P

L

Suborbital& slant path (45) are considered

Locations where some detailed ionospheric effects are assessed

A year similar to the target launch year - 2014

FRE

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TEC Reduces Significantly TEC Reduces Significantly in Low Solar Activity Yearsin Low Solar Activity Years

P

Suborbital& slant path (45) are considered

In low solar activity years (e.g., 2006), ionospheric TEC can be a factor of 5 smaller than in high activity years, and the Faraday rotation effects on L-band SAR will be reduced to minimum.

L

FRE

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The Solar Cycle Phase of the Target Launch YearThe Solar Cycle Phase of the Target Launch Year

Sunspot Maximum

1979 1990 2001 2012 2023

Sunspot Minimum

1985 1996 2007 2018 2029

Back Projection of 2014

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Ionosphere-Induced Faraday Rotation Ionosphere-Induced Faraday Rotation at Duskat Dusk A Concern in A Concern in Tropical and Mid Lat RegionsTropical and Mid Lat Regions

Ω > 10 will cause radar imaging degradation at• Low latitudes: due to large ne

• Middle Latitudes: due to Smaller θ between k & B0 dsBn

f

Kr

t

e θcos02 ∫=Ωr

r

(f = 1.257 GHz; h = 510 km; = 45; Dsw = 200 km)

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Phase Ramp at Dusk Phase Ramp at Dusk Significant in Significant in Tropical and Mid-Lat RegionsTropical and Mid-Lat Regions

• The ionospheric TEC causes phase ramp in the SAR data due to far-near range difference (200 km)

(f = 1.257 GHz; h = 510 km; = 45; Dsw = 200 km)

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TEC-Induced Apparent Target Displacement at DuskTEC-Induced Apparent Target Displacement at Duskfor L-Band (24 cm): A Concern at for L-Band (24 cm): A Concern at Low LatitudesLow Latitudes

• Target displacement of SAR images in the range direction are considerable in tropical and low latitude regions, where ionospheric TEC peaks in latitude perspective.

(f = 1.257 GHz; h = 510 km; = 45; Dsw = 200 km)

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Ionospheric Storms Ionospheric Storms A Threat to L- & P-Band InSAR MissionsA Threat to L- & P-Band InSAR Missions

TEC difference is relative to a quiet-time average using data before the storm day.

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Ionospheric Spatial Structures Ionospheric Spatial Structures during Stormsduring Storms

• Quiet ionosphere• Smooth• Small gradient

• Disturbed ionosphere• Large gradient• Curvature• Irregular structures

• Adjacent drop showing 50 TECU difference

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20% of Orbit Passes May Encounter 20% of Orbit Passes May Encounter Stormy Ionosphere in 2014Stormy Ionosphere in 2014

Year 2003 corresponds to the target launch year 2014.

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GIM – ROTI: Ionospheric IrregularitiesGIM – ROTI: Ionospheric Irregularities

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GPS L1 Scintillation in an Equatorial RegionGPS L1 Scintillation in an Equatorial Region

• October 26, 2000, at Arequipa (Peru) t = 50-Hz T = 5-min

• S4 = 0.18 ~ 0.45 = 0.22 ~ 0.45 radians (1 cycle = 2π radians)

~0.1 rad

Threshold

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GPS L1 Amplitude Scintillation and FadingGPS L1 Amplitude Scintillation and Fading

An example of detrended GPS L1 (1.57 GHz) signal power scintillation measured using a modified Turbo Rogue receiver at Santiago.

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• Scintillation receiver JPL ISM

• Location Arequipa

(Peru)

• Date 3/18/2000

GPS Scintillations Measured at Low LatitudesGPS Scintillations Measured at Low Latitudes

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L-Band Scintillation at Low LatitudesL-Band Scintillation at Low LatitudesNot a Concern for a Dawn-Dusk OrbitNot a Concern for a Dawn-Dusk Orbit

Dawn DawnDusk Dusk

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Example of Ionospheric Scintillation ScalesExample of Ionospheric Scintillation Scalesat High Latitudes during a Geomagnetic Stormat High Latitudes during a Geomagnetic Storm

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Scintillation Effects in the Auroral ZoneScintillation Effects in the Auroral ZoneA Concern to Dawn PassesA Concern to Dawn Passes

• Occurrence patterns of L-band ionospheric scintillation at Fairbanks, Alaska

• The two-way scintillation statistics is obtained by processing GPS data (50-Hz L1 signal intensity and phase, f = 1.57542 GHz) collected during 2000

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Occurrence of Azimuth Displacement due to Occurrence of Azimuth Displacement due to Scintillation Effects in the Auroral ZoneScintillation Effects in the Auroral Zone

Nominal Azimuth Resolution: 5 meters

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Ionospheric Weather Specifications Ionospheric Weather Specifications for InSAR (IWSSAR)for InSAR (IWSSAR)

• Ionospheric TEC maps using ground-based measurements It is non-trivial to obtain accurate suborbital TEC (~70% of GPS-derived

TEC) Slant-to-vertical-slant conversion error

• An ionospheric data assimilation system Dynamical modeling in space and time with assimilation of space and

ground GPS data 3-dimensional modeling to obtain integrated suborbital line-of-sight

quantities (Ω and TEC)• International Geomagnetic Reference Model (IGRF)

Empirical model to specify ambient magnetic field Perturbations generated by ionospheric currents can be neglected

(0.002% ~ a few %)• ROTI maps to specify irregularity/scintillation conditions

2-D maps of rate of TEC changes to detect ionospheric irregularities • Space-borne instruments to support IWSSAR

GPS occultation receiver and DORIS receiver; SAR itself

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Global Assimilative Ionospheric ModelGlobal Assimilative Ionospheric Model

• 3-D grid in a magnetic frame

• Global and regional modeling by solving plasma hydrodynamic equations

Numerical Scheme- Finite volume on a fixed Eulerian grid- Hybrid explicit-implicit time integration scheme

• Multiple ions: O+, H+, He+

DrivingForces

PhysicsModel

Obs. Operator

Kalman Filter

4DVAR

Assimilative Modeling TEC

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GPS Observation SystemGPS Observation System

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LEO’s Carrying GPS Occultation RCVLEO’s Carrying GPS Occultation RCV

GPS/MET

ØERSTED

GRACECOSMIC (6 LEOs)

IOX

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Ionospheric Corrections to InSARIonospheric Corrections to InSAR

• Ionospheric-induced phase variations can be obtained by integrating 4D GAIM Ne solution along radio path

• Faraday rotation can be obtained by integration of the Ne solution and an ambient magnetic field

• Modeling issue: accuracy at higher time and spatial resolutions

• Scintillation can be detected and mapped using GPS measurements

• ROTI maps can help identify contaminated InSAR data

• Modeling and measurement issues: unified irregularity maps with measurements sampled at various rates – multiple scales

Line of sight TEC

Measure of Irregularities

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ConclusionsConclusions

• Ionospheric TEC and scintillation have non-negligible effects on L-band and P-band InSAR missions

• The effects include Signal phase/delay difference due to far-near range difference in radio

ray paths Polarization changes due to Faraday rotation Target displacement or resolution degradation in range and azimuth

directions due to both TEC and scintillation TEC-induced effects in dusk passes at low and middle latitudes Scintillation-induced effects in dawn passes in auroral regions

• For an L-band mission, most of effects can be avoided by taking measurements in the dawn passes, except for scintillation in auroral regions

• For L-band dusk passes, or a P-band mission, mitigation techniques are required

• IWSSAR is an ionospheric data assimilation system that can provide the needed mitigation

• GPS occultation receiver and DORIS receiver on board spacecraft can enhance IWSSAR; using SAR itself

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AcknowledgementAcknowledgement

• This report is partially contributed by an analysis of ionospheric effects on space-based radar made by a JPL team including

Samuel Chan,

Elaine Chapin,

Bruce Chapman,

Curtis Chen,

Yunjin Kim,

Jan Martin,

Thierry Michel,

Ron Muellerschoen,

Xiaoqing Pi,

Paul Rosen,

and Mike Spencer.

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