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GISMO Mission Options

GISMO 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

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GISMO Mission Options

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  1. GISMO 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 XPI@JPL: IWSSAR Strategy

  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 • ReflectorWidth: 7 m • Geolocation Accuracy: < 10 m • Calibration: 1 - 1.5 dB absolute, • 0.5 - 1.0 relative • Noise Equivalent 0: < -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 XPI@JPL: IWSSAR Strategy

  3. Eagle Scout Mission P-Band SAR XPI@JPL: IWSSAR Strategy 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 XPI@JPL: IWSSAR Strategy 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 ( = 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 XPI@JPL: IWSSAR Strategy

  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 XPI@JPL: IWSSAR Strategy

  8. Effects due to TEC 1 TECU (= 1016 electrons/m2) Corresponds to (one way) • 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 ∆rbetween 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 > 20 TECU, L-band; 2.54 TECU, P-band) • Typical suborbital daytime TEC can reach 20 to ~100 TECU The estimation of Faraday rotation () uses  = 45 and B0 = 0.4 gauss, which in general vary with geographic location and radio geometry. XPI@JPL: IWSSAR Strategy

  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 FRE Ascension Island L P Suborbital & slant path (45) are considered UT (tick mark = 1 hour) XPI@JPL: IWSSAR Strategy

  10. Latitudinal Variation of the IonosphereA Concern at Low and Mid Latitudes Locations where some detailed ionospheric effects are assessed FRE L Most of blue areas are not a concern for the Faraday rotation effect at L-band P Suborbital & slant path (45) are considered A year similar to the target launch year - 2014 Dawn (ascending) Dusk (descending) XPI@JPL: IWSSAR Strategy

  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 smallerthan in high activity years, and the Faraday rotation effects on L-band SAR will be reduced to minimum. XPI@JPL: IWSSAR Strategy

  12. The Solar Cycle Phase of the Target Launch Year Back Projection of 2014 XPI@JPL: IWSSAR Strategy

  13. Ionosphere-Induced Faraday Rotation at DuskA Concern in Tropical and Mid Lat Regions (f = 1.257 GHz; h = 510 km;  = 45; Dsw = 200 km)  > 10 will cause radar imaging degradation at • Low latitudes: due to large ne • Middle Latitudes: due to Smaller  between k & B0 XPI@JPL: IWSSAR Strategy

  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) XPI@JPL: IWSSAR Strategy

  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. XPI@JPL: IWSSAR Strategy

  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. XPI@JPL: IWSSAR Strategy

  17. Ionospheric Spatial Structures during Storms • Quiet ionosphere • Smooth • Small gradient • Disturbed ionosphere • Large gradient • Curvature • Irregular structures • Adjacent drop showing 50 TECU difference XPI@JPL: IWSSAR Strategy

  18. 20% of Orbit Passes May Encounter Stormy Ionosphere in 2014 Year 2003 corresponds to the target launch year 2014. XPI@JPL: IWSSAR Strategy

  19. GIM – ROTI: Ionospheric Irregularities XPI@JPL: IWSSAR Strategy

  20. GPS L1 Scintillation in an Equatorial Region • October 26, 2000, at Arequipa (Peru) • t = 50-Hz T = 5-min • S4 = 0.18 ~ 0.45 sf= 0.22 ~ 0.45radians (1 cycle = 2 radians) ~0.1 rad Threshold XPI@JPL: IWSSAR Strategy

  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. XPI@JPL: IWSSAR Strategy

  22. GPS Scintillations Measured at Low Latitudes • Scintillation receiver • JPL ISM • Location • Arequipa (Peru) • Date • 3/18/2000 XPI@JPL: IWSSAR Strategy

  23. L-Band Scintillation at Low LatitudesNot a Concern for a Dawn-Dusk Orbit Dawn Dusk Dawn Dusk XPI@JPL: IWSSAR Strategy

  24. Example of Ionospheric Scintillation Scalesat High Latitudes during a Geomagnetic Storm XPI@JPL: IWSSAR Strategy

  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 XPI@JPL: IWSSAR Strategy

  26. Occurrence of Azimuth Displacement due to Scintillation Effects in the Auroral Zone Nominal Azimuth Resolution: 5 meters XPI@JPL: IWSSAR Strategy

  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 XPI@JPL: IWSSAR Strategy

  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 4DVAR Kalman Filter TEC Assimilative Modeling XPI@JPL: IWSSAR Strategy

  29. GPS Observation System XPI@JPL: IWSSAR Strategy

  30. LEO’s Carrying GPS Occultation RCV GPS/MET ØERSTED COSMIC (6 LEOs) GRACE IOX XPI@JPL: IWSSAR Strategy

  31. 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 Ionospheric Corrections to InSAR Measure of Irregularities Line of sight TEC XPI@JPL: IWSSAR Strategy

  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 XPI@JPL: IWSSAR Strategy

  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. XPI@JPL: IWSSAR Strategy

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