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Glaciers and Ice Sheet Interferometric Radar

Glaciers and Ice Sheet Interferometric Radar

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Glaciers and Ice Sheet Interferometric Radar

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  1. Glaciers and Ice Sheet Interferometric Radar April 2007 Planning Meeting Wallops Flight Facility October 10, 2006

  2. October 10 - Agenda • Meeting to Begin at 10 AM • GISMO Introduction • 10:00  Meeting objectives Jezek • 10:10 GISMO Overview:  Jezek • May 2006 Experiment • 10:15 May 2006 Experiment Objectives Jezek • 10:30 May 2006 lessons learned for Radar:  Gogineni • 11:00 May 2006 lessons learned for navigation:  Sonntag • 11:30 Minutes data processing status:  Jezek • 11:45 break for lunch • April 2007 Experiment • 13:00 Experiment Overview – Jezek 10 min • 13:10 April 2007 Radar status (150 and 440 Mhz electronics, racks, cables, antennas):  Gogineni discussion of antenna mods, cable mods, rack layout, etc. • 13:40 April 2007 proposed flight tracks and navigation requirements Jezek • 14:10 April 2007 Wallops requirements on GISMO - eg. flight request paper work, Danish [Greenland Home Rule] approval, airworthiness approvals, costs:  Krabill, Guillory, Valliant • 14:50 Break • 15:00 Scheduling priority issues, leading to logic diagram for selecting flight profile for a given day – Krabill • 15:30 Schedule of events and milestons for April flights - Jezek • 1545 2007-2008 Plans and Meeting Action Items Jezek • 1700 Telecon with JPL and Vexcel

  3. Meeting Objectives • Review Project Goals and Status • Summary of May 2006 Experiment • Objectives of April 2007 Airborne Experiment • Aircraft Configuration • Airborne Experiment Design • Navigation and location • Proposed flight lines • Schedule • Flight Planning Guidance and Milestones • Costs

  4. GISMO Project Status K. Jezek

  5. Global Ice Sheet Interferometric Radar (GISIR) PI: Prof. Kenneth C. Jezek, The Ohio State University Objective Filtered basal inferogram InSAR Concept • Develop and test radars and algorithms for imaging the base of the polar ice sheets • Investigate interferometric and tomographic clutter rejection and basal imaging methods • 3-d topography of the glacial bed • Images of subglacial conditions • Develop multiphase center P-band and VHF radars • Capable of sounding 5 km of ice • Single and repeat pass interferometric operation • Assess the requirements for extension to continental scale campaigns Repeat pass tomography Approach Key Milestones • Use available topography data to simulate interferograms for testing the InSAR and tomographic concepts. • Modify the SAR simulator to include operating characteristics of several aircraft and several radar designs • Develop UHF and VHF radars and antenna systems • Test methodology by collecting data over the Greenland and Antarctic ice sheets • Algorithm validation and sensitivity assessment. 1/ 06 Phase History Simulations and Algorithm Testing 5/06 First flight test in Greenland (Twin Otter 150 MHz) 9/06 Radar and Antenna Development 7/06 InSAR and tomography algorithm refinement 5/07 Greenland Field Campaign (NASA P-3) 5/08 Second Greenland Campaign (NASA P-3) 6/08 Algorithm and methodology assessment 7/08 Requirements doc. for continental scale imaging Co-Is:E. Rodriguez, JPL; P. Gogineni, U. Kansas; J. Curlander, Vexcel Corp.; John Sonntag, EG&G; C. Allen, U. Kansas; P. Kanagaratnam, U. Kansas TRLin =3 http://esto.nasa.gov

  6. Project Accomplishments • Theoretical concept well defined • Phase history simulations confirm theoretical predictions • Radar design trade completed • Scaling study completed • Limited radar system deployed for May 06 test flight in Greenland • Data acquired and successfully processed to SAR images and interferograms

  7. Year 2 Project Goals • Radar Development : Build sub-system and assemble the complete system. Perform laboratory tests using delay lines to document loop sensitivity,radar waveforms and impulse response. • System Integration (KU, WFF, Aircraft Operator) a)Install the radar and navigational equipment on P-3 or similar aircraft and conduct flight tests over the ocean. • Algorithm Development. Develop a strip IFSAR processor and compare against the results of the exact time-domain processor. Iterate the clutter removal algorithm based on experimental results (JPL). Develop software and apply software to process multiple 2-D complex SAR images coherently (Vexcel). • Data acquistion and Analysis : Field experiments over the ice sheet; Finalize interferometric SAR processor and pre-processor and process data from first campaign (JPL). Extract basal topography from result.. Iterate interferometric filter design based on assessment of the results. • Science and Management : Participate in field measurements; Conduct design and performance review; assess quality of results in context of science requirements.

  8. May 2006 Experiment Summary

  9. May 2006 Experiment Summary and Objectives • Flight of opportunity to acquire early GISMO data • Data acquired using KU 140 MHz radar and WFF navigation equipment • Single pass and repeat pass data acquired • Objectives in priority order: • investigate whether data of suitable signal strength and with suitable knowledge of aircraft navigation parameters could be acquired for successful InSAR processing for measurements of basal topography and reflectivity; • evaluate phase filtering clutter rejection concept; • evaluate tomographic imaging concept for clutter rejection • Evaluate clutter rejection using multiple antenna elements

  10. May 06 Experiment • Twin otter flight from Thule: Camp Century; interior • 150 MHz Radar • 5 transmit and 5 receive elements (1 m spacing) • ~ 2 m baseline outbound (achieved 7 m) • Return flight offset 25 m to the south for larger baseline • Maximum comfortable altitude (achieved 3000 m) • Range window setting procedure

  11. May 06 flight route

  12. May 06 Data Processing Status

  13. Range and Azimuth Compressed Slant Range Images (log scale) Base Left Wing Right Wing Internal Layers Surface

  14. 140 MHz Interferogram Base surface noise layers

  15. May 06 Data ProcessingLessons Learned • 1) Single pass, across track SAR imaging from aircraft is possible even in areas where the base of the ice sheet appears to be relatively smooth. We will analyze the rest of the May 23 data set to investigate the range of relative backscatter values observable along this flight path. • 2) Across track interferometry is possible in the area where backscatter is relatively weak. This is consistent with theory. We will investigate whether the fringe rates we observe are reasonable for the short (7 m) baseline we achieved on the Twin Otter aircraft. • 3) Given the measured fringe rate patterns, we will investigate whether we can retrieve across track measurements of basal topography. • 4) Data processed so far steer the beam 20 degrees off nadir. Depending on the product of the beam pattern with the backscatter falloff, this may or may not be optimum. We will analyze the data with different degrees of beam steering. • 5) We did not observe fringes from the ice sheet surface in the most recently processed data. Yet we can clearly see internal layers, which should have a much lower backscatter value than the surface return. We will investigate how beam steering angle influences the measured backscatter from the ice sheet surface. Are there blanking signals or AGC cirucuits that reduce the surface return? • 6) We observe detailed internal layers in the range and azimuth compressed data. We also observed the frequently described internal layer free zone near the base of the ice sheet. Are the returns solely from nadir or are we imaging the layer surface? • 7) 140 MHz backscatter strength is sufficient to yield a measurable signal. We will test and compare 140 MHz and 440 MHz systems. • 8) The May 23 data collected observations along the same in and out bound track. We will investigate how longer baselines derived from repeat pass data effect data quality. • 9) We observed a systematic noise pattern in the amplitude and interferometric data. The noise artifacts in the InSAR data will be an additional complication for interferogram filtering. The noise source is not always on and we will attempt to identify the origin of the noise source.

  16. GISMO Flights 07-08 Plans and Objectives

  17. Technical Objectives for April ’07 Experiment • 1) Acquire data over the May 2006 flight line to compare high and low altitude observations and to compare interferometry acquired with different baselines. Are results consistent with theory? • 2) Acquire data at 140 MHz and 440 MHz along every flight line and compare backscatter and interferometric frequency response? Are the results consistent with theory? • 3) Acquire data over areas where we expect to find subglacial water. Is water detectable either from backscatter maps or from topography? • 4) Acquire data over regions of increasing surface roughness. This may require observations over heavily crevassed shear margins such as those found around Jacobshavn Glacier. Can we successfully implement interferogram phase filtering? • 5) Acquire data for tomographic analysis • 6) Investigate repeat pass interferometry over repeat periods of days. • 7) Verify volume clutter is weak (all snow zones) • 8) Collect data over thick and thin ice to test for absorption effects

  18. April 07 Experiment • P-3 flights from Thule and Kangerdlussuaq • 150 MHz and 440 MHz Radars • Define antenna spacing • Define outbound baseline • Return flight offset 25 m to the south for larger baseline • Maximum altitude allowable • Range window setting procedure

  19. Update to May 06 Experiment Plan

  20. Aircraft Configuration

  21. P-3 Modifications • Multiple conductors to antenna array (one conductor used in past experiments) • Additional antenna elements beneath wings • Additional element in the tail • GPS and Inertial navigation information on aircraft position and attitude

  22. Cable Spec’s SMA (2x) on BPE240, bundled With polyolefin jacket

  23. Airborne Experiment Design

  24. Single Pass Interferometry Maximize altitude Maximize antenna array separation 6 km swath

  25. Multi-Pass SAR Imaging Synthetic Aperture Synthetic Elevation Aperture Ground Reference Point

  26. Constraints on Flight Operations • Fly at maximum allowable altitude • Limit flight duration to allow for daily data Q/A and experiment modifications (about 6 hours assuming 150 Gb/hour and 3, 300 Gb disks) • Allow enough field time to repeat flight lines • Fly over high and low clutter areas • Fly over areas where some information on basal properties is known • VHF and UHF radars cannot operate simultaneously – P-band outbound; VHF inbound along same track to within 30 m • Schedule 2 to 4 repeat flights at 30 m horizontal offsets for tomography

  27. Aircraft NavigationExpected Performance • 20 m ground track repeatability • 0.02 degree post flight knowledge on aircraft roll and pitch • 1 degree post flight knowledge on yaw

  28. Proposed Flight Lines

  29. Flight Description • Inbound flight displaced 25 m from outbound flight • Each flight flown twice: 150 and 440 MHz • Flight 1 is highest priority at 440 Mhz • Each flight is between 2000 and 2500 km (roundtrip) • Flights 1 and 2 include segments over the ocean • Flight 3 should include a segment down the Sondrestrom Fjord

  30. Flight 1 and 2

  31. Flight 3

  32. Preliminary list of actions

  33. IPY Flight Request