GISMO Mission Options

1
GISMO Mission Options

• Decadal Survey did not call for a P-Band
  capability
• But did open up the idea of Venture Missions
  costing lt 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 missions timeline (in sat 2016) to
  acquiring GISMO data in repeat-pass mode
• Parallel development could be the Mars Science
  Orbiter payload

2
P-band Radar Instrument Concept(for Veg. 3-D
structure)
Instrument Features

• 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 lt 10 m
• Calibration 1 - 1.5 dB absolute,
• 0.5 - 1.0 relative
• Noise Equivalent ?0 lt -30 dB

9m Astromesh Reflector
Boom
Solar Array
Phased Array Feed
Stowed Reflector Support Towers
Technology
Airborne Simulation of P-band Polarimetric Data

• 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

3
Eagle Scout Mission
P-Band SAR
Combines Polarimetry and Repeat-pass
Interferometry to characterize Martian subsurface
4
Eagle Scout Mission
Received a Category I rating in the latest Mars
Scout proposal review - possible 2013 Orbiter
payload?
P-Band SAR
Combines Polarimetry and Repeat-pass
Interferometry to characterize Martian subsurface
5
Ionospheric Weather Specifications for InSAR
(IWSSAR)
Xiaoqing Pi Jet Propulsion Laboratory
JPL, November 14, 2006
6
Outline

• Ionospheric Effects on L-Band SAR InSAR at dusk
  
• TEC-induced near-to-far range phase ramp (??
  15200 rad) and suborbital Faraday rotation
  (520?)
• Ionospheric weather TEC variations (?TEC 50
  100, or 50100) and scintillation (?? 0.11
  rad)
• Effects on estimate of target displacement 510
  meters due to TEC, and a few 10s 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

7
Ionospheric Effects
Phase or Delay
Phase Amplitude Scintillation
?? and ?A are random fluctuations
Line-of-sight TEC
Faraday Rotation
Scintillation Statistics for Signal
Intensity and Phase

• ne - electron density
• B0 - ambien mag. field
• - angle between k and B0
• K 2.365?104 (in MKS units)

Frequency Dependence
8
Effects due to TEC
1 TECU ( 1016 electrons/m2) Corresponds to (one
way)
? The estimation of Faraday rotation (?) uses ?
45? and B0 0.4 gauss, which in general vary
with geographic location and radio geometry.
? (m) / f (GHz) ? (rad/?) ?? (?)
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 quality of radar data synthesis is sensitive
  to the ionospheric-induced effects of (two way)
• ?? ? 90? or 1.57 rad (suborbital TEC gt 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 )
• ? ? 10? (suborbital TEC gt 20 TECU, L-band 2.54
  TECU, P-band)
• Typical suborbital daytime TEC can reach 20 to
  100 TECU

9
Diurnal Variation of the Ionospherethe Concern
of Dusk Effect
Minimum at dawn a dawn orbit to avoid
ionospheric effects
Dusk
1980
Day to day variability at dusk a threat to InSAR
20 TECU
TEC
Dawn
Ascension Island
FRE
L
P
Suborbital slant path (45?) are considered
UT (tick mark 1 hour)
10
Latitudinal Variation of the IonosphereA Concern
at Low and Mid Latitudes
Locations where some detailed ionospheric
effects are assessed
FRE
L
P
Suborbital slant path (45?) are considered
A year similar to the target launch year - 2014
Dawn (ascending)
Dusk (descending)

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

11
TEC Reduces Significantly in Low Solar Activity
Years
L
FRE
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.
12
The Solar Cycle Phase of the Target Launch Year
Back Projection of 2014
Sunspot Maximum 1979 1990 2001 2012 2023
Sunspot Minimum 1985 1996 2007 2018 2029
13
Ionosphere-Induced Faraday Rotation at Dusk A
Concern in Tropical and Mid Lat Regions
(f 1.257 GHz h 510 km ? 45? Dsw 200 km)

• ? gt 10? will cause radar imaging degradation at
• Low latitudes due to large ne
• Middle Latitudes due to Smaller ?
  between k B0

14
Phase Ramp at Dusk Significant in Tropical and
Mid-Lat Regions
(f 1.257 GHz h 510 km ? 45? Dsw 200 km)

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

15
TEC-Induced Apparent Target Displacement at
Duskfor L-Band (24 cm) A Concern at Low
Latitudes
(f 1.257 GHz h 510 km ? 45? Dsw 200 km)

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

16
Ionospheric Storms A Threat to L- P-Band InSAR
Missions
TEC difference is relative to a quiet-time
average using data before the storm day.
17
Ionospheric Spatial Structures during Storms

• Quiet ionosphere
• Smooth
• Small gradient
• Disturbed ionosphere
• Large gradient
• Curvature
• Irregular structures
• Adjacent drop showing 50 TECU difference

18
20 of Orbit Passes May Encounter Stormy
Ionosphere in 2014
Year 2003 corresponds to the target launch year
2014.
19
GIM ROTI Ionospheric Irregularities
20
GPS L1 Scintillation in an Equatorial Region
0.1 rad
Threshold

• October 26, 2000, at Arequipa (Peru)
• ?t 50-Hz T 5-min
• S4 0.18 0.45 sf 0.22 0.45 radians (1
  cycle 2? radians)

21
GPS 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.
22
GPS Scintillations Measured at Low Latitudes

• Scintillation receiver
• JPL ISM
• Location
• Arequipa (Peru)
• Date
• 3/18/2000

23
L-Band Scintillation at Low LatitudesNot a
Concern for a Dawn-Dusk Orbit
Dawn
Dawn
Dusk
Dusk
24
Example of Ionospheric Scintillation Scalesat
High Latitudes during a Geomagnetic Storm
25
Scintillation Effects in the Auroral ZoneA
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

26
Occurrence of Azimuth Displacement due to
Scintillation Effects in the Auroral Zone
Nominal Azimuth Resolution 5 meters
27
Ionospheric Weather Specifications 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 (? 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

28
Global Assimilative Ionospheric Model

• 3-D grid in a
• magnetic frame

• Multiple
• ions
• O,
• H,
• He

Numerical Scheme - Finite volume on a fixed
Eulerian grid - Hybrid explicit-implicit time
integration scheme
Driving Forces
Physics Model
Obs. Operator

• Global and
• regional modeling
• by solving plasma
• hydrodynamic
• equations

Kalman Filter
4DVAR
TEC
Assimilative Modeling
29
GPS Observation System
30
LEOs Carrying GPS Occultation RCV
GPS/MET
ØERSTED
COSMIC (6 LEOs)
GRACE
IOX
31
Ionospheric Corrections to InSAR
Measure of Irregularities
Line of sight TEC

• 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

32
Conclusions

• 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

33
Acknowledgement

• 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.