Joel T. Johnson, K. C. Jezek , L. Tsang, C. C. Chen, M. Durand, G. Macelloni

1. UWBRAD: Ultra-Wideband Software-Defined Microwave Radiometer for Ice Sheet Subsurface Temperature Sensing Joel T. Johnson, K. C. Jezek, L. Tsang, C. C. Chen, M. Durand, G. Macelloni Year 1 Interim Review Meeting 24th October 2014 Columbus, OH

2. Review Goals The PI must provide a presentation summarizing the work accomplished and results leading up to this Interim Review and must: 1. Describe the primary findings, technology development results, and technical status, e.g., status of design, construction of breadboards or prototype implementations, results of tests and/or proof-of-concept demonstrations, etc.; 2. Describe the work planned for the remainder of the project and critical issues that need to be resolved to successfully complete the remaining planned work; 3. Summarize the cost and schedule status of the project, including any schedule slippage/acceleration. A schedule milestone chart of all major task activities shall be created and maintained and shown at all reviews. A cost data sheet shall be created and maintained, showing total project costs obligated and costed, along with a graphical representation of the project cost profile to completion; 4. Provide a summary of anticipated results at the end of the task; and 5. At the second review and subsequent reviews, address the comments and recommendations prepared by the reviewers participating in the most recent review.

3. Agenda 0930-0950 Overview of project status 0950-1010 Forward modeling/retrieval investigations 1010-1025 Radiometer front end design status 1025-1045 Digital backend and software status 1045-1105 Antenna design status 1105-1115 Experiment planning 1115-1130 Discussion

4. UWBRAD: Ultra-Wideband Software-Defined Microwave Radiometer for Ice Sheet Subsurface Temperature Sensing Objectives: • Design, develop, test & validate an ultra-wide band, 0.5-2.0 GHz software defined microwave radiometer for sensing ice sheet internal temperature at depth • Develop software defined algorithms for real time RFI mitigation enabling operation outside protected bands • Design, develop, test & validate a new aircraft 0.5-2 GHz antenna • Conduct ground based & airborne demonstrations of UWBRAD; flights on a Twin Otter in Greenland • Conduct science demonstration/validation of UWBRAD results • Develop an experiment plan for deployment of UWBRAD to support future science observations of ice sheet temperatures • Assess adaptation of instrument to other air and space platforms • Address key NASA climate variability and change issues (left) 1.4 GHz SMOS Antarctic brightness temperatures showing cold anomaly at Lake Vostok (black outline)(right) Pure ice penetration depth vs. frequency and temperature Approach: Key Milestones: • UWBRAD is a .5-2 GHz nadir observing radiometer having 15 x 100 MHz fully digitized channels for RFI detection and mitigation • Design, construct and demonstrate two channel system in year 1 • Design, construct, and test scale model of antenna in year 1 • After initial tests, expand radiometer to 15 channels and test radiometer performance, software defined algorithms, cognitive radiometry, and full scale antenna in lab environment • Develop and apply multi-frequency, model based retrieval algorithms to determine internal ice sheet temperatures • Conduct flight demonstration in 2016 to validate technologies and science capabilities • Assess science and technical data to develop a plan for integration of UWBRAD into NASA science mission • Co-Is/Partners: K. Jezek (OSU), C. Chen (OSU), M. Durand (OSU), L. Tsang (University of Washington) • Complete Detailed System Design 10/2014 • Complete Dual Channel Implementation/Test 4/2015 • Complete Antenna Scale Model Fabrication/Test 4/2015 • Complete 15 Channel Implementation/Test 10/2015 • Complete Antenna Implementation/Test 10/2015 • Complete Laboratory Tests of Full System 4/2016 • Conduct Airborne Experiments 12/2016 • Complete Data Analysis 4/2017 TRLin= 3 , TRLout= 5

5. Project Team • OSU ElectroScience Laboratory, Department of Electrical and Computer Eng. • PI Prof. Joel T. Johnson • Co-PI Prof. Chi-Chih Chen (Antenna) • Research Associate: Mark Andrews (Radiometer Hardware/Software) • Postdoctoral Researcher: Alexandra Bringer (Modeling/Retrieval) • Research Scientists: Dr. CaglarYardim (Modeling/Retrieval) and Dr. Brian Dupaix (Digital subsystem) • Graduate Student: Mustafa Aksoy (RFI algorithms) • Graduate Student: Domenic Belgiovane (Antenna) • Technician: Jim Moncrief (Radiometer build/test) • OSU Byrd Polar Research Center, School of Earth Sciences • Science PI Prof. Ken C. Jezek (RT modeling/science/campaign planning) • Co-PI Prof. Michael C. Durand (Retrieval algorithms/science) • Graduate Student: YunaDuan (Retrieval algorithms/science) • University of Washington, Department of Electrical and Computer Eng. • Co-PI Prof. Leung Tsang (Advanced RT modeling) • Graduate Students:ShurunTan, Tian-Lin Wang (Advanced RT modeling)

6. Project Team (cont’d) and Status • Independent Contractor: Dr. Vladimir Leuski (Radiometer Front end design/build) • Collaborators: Drs. Giovanni Macelloni and Marco Brogioni (CNR-IFAC, Italy) • (Science/RT modeling/campaign planning) • Collaborators (not official): Drs. Mark Drinkwater, ESA, LudovicBrucker, GSFC • Status: • Start date 4/1/14, but project not in place officially at OSU until 5/1/14 • Spending rate will increase in remainder of year 1 due to: • - full team now in place • - parts and hardware purchases • Expect to be back on track (to • within 1 month of budget) by year end • Still progressing to milestones on schedule

7. Milestones and Timeline

8. Milestones and Timeline

9. Milestones and Timeline 8/15: Delivery to Italy needed for potential participation in FY16 ESA DOME-C Tower measurements

10. TRL Status

11. Motivation • Understanding dynamics of Earth’s ice sheets important for future prediction of ice coverage and sea level rise • Extensive past studies have developed a variety of sensing techniques for ice sheet properties, e.g. thickness, topography, velocity, mass, accumulation rate,… • Limited capabilities for determining ice sheet internal temperatures at present • Available from small number of bore holes • Internal temperature influences stiffness, which influences stress-strain relationship and therefore ice deformation and motion • Can ice sheet internal temperaturesbe determined using microwave radiometry?

12. Ultra-wideband software defined radiometer (UWBRAD) We propose design of a radiometer operating 0.5 – 2 GHz for internal ice sheet temperature sensing Requires operating in unprotected bands, so interference a major concern Address by sampling entire bandwidth (in 100 MHz channels) and implement real-time detection/mitigation/use of unoccupied spectrum Supported under NASA 2013 Instrument Incubator Program Goal: deploy in Greenlandin 2016 Retrieve internal ice sheettemperatures andcompare with in-situcore sites

13. UWBRAD Science Goals • Measurement of ice sheet physical temperature at 10 m depth to 1 K accuracy at minimum 10 km spatial resolution • 10 m temperatures approximate the mean annual temperature, an important climate parameter. • Measurement of depth-averaged physical temperature from 200 m to maximum 4 km ice sheet thickness to 1 K accuracy at minimum 10 km spatial resolution • Spatial variations in average temperature can be used as a proxy for improving temperature dependent ice-flow models. • Measurement of ice sheet physical temperature profile at 100 m depth intervals to 1 K accuracy at minimum 10 km spatial resolution • Remote sensing measurements of temperature-depth profiles can substantially improve ice flow models. • Measurements time coded and geolocated by latitude and longitude.

14. MODELING/ RETRIEVAL STUDIES

15. Ice Sheet Temperature Properties A simple model of ice sheet internal temperatures is (assumes homogeneous ice driven by geothermal heat flux, no lateral advection) Temperature increases with depth; more rapid increase for lower M Can reach melting point in some cases 15

16. Ice Sheet Properties • Upper layer of ice sheet comprised of snow: high volume fraction of ice crystals in air • “Dense medium” from electromagnetic point of view • Mass density of snow determines volume fraction of ice • Medium typically represented as air containing spherical ice particles • Particle radius typically characterized by the “grain size” parameter • Density on average increases with depth • Volume fraction of ice increases and passes 50% at ~ several m depth • Medium is now air inhomogeneities in ice background • Inhomogeneity volume fraction on average decreases with depth past this point • Grain size increases with depth • Medium on average approaches homogeneous ice at depths ~ 100 m • “Random” variations in density and composition with depth on top of the average trends can appear as “layering” effects

17. Emission Physics • In absence of scattering, thermal emission from ice sheet could be treated as a 0th order radiative transfer process • Similar to emission from the atmosphere: temperature profiling possible if strong variations in extinction with frequency (i.e. absorption line resonance) • Ice sheet has no absorption line but extinction does vary with frequency • Motivates investigating brightness temperatures as function of frequency • Inhomogeneities causing scattering or other layering effects are additional complication • Need models that can captureeffect of scatterers

18. DMRT-ML Model TB varieswith internalT(z) Scatterersless importantat lower frequencies Lower frequencies“see” warmer iceat greater depths • DMRT-ML model (Picard et al, 2012) widely used to model emission from ice sheets (Brucker et al, 2011a) and snowpacks (Brucker et al, 2011b) • Uses QCA/Percus-Yevickpair distribution for sticky or non-sticky spheres • RT equation solved using discrete ordinate method • Need layer thickness, temperature, density, and grain size for multiple layers • Recommended grain size is 3 X in-situ measured grain sizes • DMRT-ML computed results for DOME-C density/grain size profiles vs. frequency

19. Progress to Date • Expanded assessment of forward models • Intercomparison of “cloud”, DMRT-ML, MEMLS, and coherent codes to understand importance of coherent effects • Incorporation of effects of density fluctuations • Incorporation of effects of UWBRAD antenna pattern • Consideration of geophysical cases similar to Greenland in addition to Antarctica • Initial retrieval study for Greenland cases • Initial expansion of retrieval framework • Formulation in terms of desired and nuisance parameters • Formulation of CRLB • Investigation of ancillary data sources and their impact

20. Forward Model Assessment Cloud DMRT/MEMLS Coherent • Used “Dome-C”-type physical parameters • Including density fluctuations with correlation length parameter • Results show: • Coherent effects can be significant if density correlation length << wavelength; otherwise good agreement between models • No significant differences between DMRT/MEMLS • Paper submitted to TGRS

21. Comparison with SMOS • Model predictions compared with SMOS observations of Dome-C • Fixed frequency (1.4 GHz), multi-angle and dual polarization • Ground truth data from Dome-C on density properties incorporated (upper layers only) and temperature profile • Including density fluctuations important to reproduce data; coherence has only small impact • Larger errors at H-polat larger angles possiblydue to interface roughnesseffects • UWBRAD willemphasize near nadiralobservations wherematch is better • Similar results reported by M. Brogioni and G. Macelloni at IGARSS14

22. Initial Retrieval Studies for Greenland • Past retrieval study focused on Antarctic geophysical cases • Low accumulation rates resultin temp profiles that increase withdepth • Strong changes in TB vs. frequency • Higher accumulation rates in Greenland (at leastfor GISP site)result in moreuniform temp profilevs. depth • Smaller changes inTB vs. frequency • Still observableby UWBRAD Antarctica Greenland(GISP) Greenland(GISP)

23. Greenland Retrieval Studies • Generated simulated UWBRAD observations “GISP-like” ice sheets for varying physical properties (480 “truth” cases) • Including averaging over density fluctuations • For each truth case, generate 100 simulated retrievals with UWBRAD expected noise levels (i.e. ~ 1 K measurement noise per ~ 100 MHz bandwidth) • Select profile “closest” to simulated data as the retrieved profile, and examine temperature retrieval error • Errors in this simulation meet science requirements • Additional simulations needed with wider range of Greenland cases • Currently examining Operation IceBridge Greenland ground truth data along expected flight path

24. Expansion of Retrieval Framework • A variety of approaches are being examined and implemented by the retrieval team to improve retrieval performance • Estimating CRLB for given geophysical case • Consideration of ancillary information incorporation, e.g. surface temperature, ice sheet thickness, density profiles (couple with RACMO model?) • Reformulation of problem in terms of desired science products and nuisance parameters • Other retrieval methods are under investigation as well • MCMC method • Work will continue as part of task 2 effort • Greenland cases emphasize importance of robust retrieval process and careful instrument design

25. RADIOMETER DESIGN

26. Radiometer Design 15 channel“pseudo-correlation” designfrom proposal • Three major subsystems: front end, digital backend, antenna • Front end: • Low frequencies of interest enable board-level implementation • Traditional Dicke-switch design requires isolators to stabilize amp input impedance • Not easily available for 2:1 or more bandwidth • Recent “pseudo-correlation” designs eliminate need for isolator

27. Front End Progress • Review of radiometer frequency plan completed • Based on RFI considerations, 15 adjacent channel frequency plan revised to 13 separated channels in 2ndNyquist of ADC • Trade study of alternate radiometer front end design based on Dicke Switch architecture also completed • Baseline “hybrid” radiometer design updated to include RF filtering • Build of “Hybrid radiometer” LNA/hybrid block in progress to assess performance

28. Revised Front End Design (13 channels)

29. Initial LNA Tests LNA components (2 amplifier sequence) for use in UWBRAD ordered and tested to verify performance Found to meet factory specifications

30. Digital Subsystem • Digital Subsystem based around the ATS9625 card from AlazarTech, Inc. • 2 channel, 250 MSPS by 16 bit data acquisition card • Achieves high throughput to host PC • Team has past experience with similar AlazarTechboard and software interface • RFI processing to be performed on host PC • Each board can handle 2 100 MHz channels;8 boards used for 15 channels • One host PC can accommodate 2 ATS9625 boards • Need 4 PC’s • Early acquisition of 2 boards and host PC will be used for throughput and softwarestudies

31. Digital Subsystem Status • An RF hybrid that was planned to be used in the mixing stage immediately prior to the analog to digital converter (ADC) boards was obsolete and no suitable replacement could be found • Impact: Could no longer downconvertthe signals of interest to baseband • A trade was conducted to determine whether a wideband (12 bit/sample, 2 GS/s) ADC could be used without downconversion, or if it would be better to use a wider bandwidth version of the current board (16 bit/sample, 250 MS/s) at an IF in the first Nyquist zone (125-250 MHz) • Evaluation boards from both suppliers were procured and tested • Agilent U5303A for 2GS/s board, AlazarTech ATS9625 for 250 MS/s board • Results of testing showed that the AlazarTech board had superior performance for measuring radiometric signals • Impact: RF subsystem modified to use first Nyquist zone of AlazarTech boards

32. Radiometric Stability Testing – Amplified Noise Power

33. Radiometric Stability Testing – Free Running Noise Power

34. Digital Subsystem Summary • Still using the AlazarTech board from the proposal, but requires modification to increase the input bandwidth of the board to 250 MHz • AlazarTech board shows good radiometric performance at long averaging times • Two initial boards obtained, installed and tested • One channel of one board requires repair, other three channels working well • Software work proceeding with the AlazarTech boards

35. Software Status • Initial flow charts have been created to guide the structure and planning for software development • Currently two separate programs: Acquire and Process • Acquire focuses on interacting with the ADC boards and recording the data • First iteration of Acquire code complete • Process focuses on RFI mitigation and extracting power/brightness temperature information from data • First iteration of Process code in progress • May add a third Host program in the future for coordinating the system functions and presenting data to the user

36. Acquire Flow Chart

37. Acquire Program Output • Currently measures antenna two times for each calibration sequence • ~10% duty cycle for antenna data recording, ~5% duty cycle for full sequence • Possible paths for improvement: • Increase number of antenna measurements per calibration to increase duty cycle • Avoid writing calibration data to disk and just calculate coefficients • Use Solid State Drive for initial disk write (~0.5x write time), move from SSD to HDD when complete • Write data from different boards to different HDDs

38. Process Flow Chart

39. Software Summary Interface to AlazarTechboards well understood and documented Software architecture plan has been created and guiding development First iteration of data acquisition program complete and provides solid base for future improvements Data processing code in initial stages of creation

40. Antenna Update

41. Conical Spiral Antenna Operations Base =7.2” Length=30” 20 turns GND=12” Dia. Constant Symmetric Gain Patterns <animation> <Animation> 0.6-2.0 GHz@0.1 GHz Steps 0.5-2.0 GHz@0.1 GHz Steps

42. Adjustable Gain and Beamwidth vs. Turns Base =7.2” Height=30” 20 turns GND=12” Dia. 0.5 GHz 0.5-2.0 GHz@0.1 GHz Steps 0.5 GHz Base =7.2” Height=30” 30 turns GND=12” Dia. 0.5-2.0 GHz@0.1 GHz Steps

43. Adjustable Gain and Beamwidth vs. Height Base =7.2” Height=36” 30 turns GND=12” Dia. 0.5 GHz 0.5-2.0 GHz@0.1 GHz Steps Base =7.2” Height=30” 30 turns GND=12” Dia. 0.5 GHz 0.5-2.0 GHz@0.1 GHz Steps

44. Field Program Update Antarctica, Greenland, Russian/Canadian ice caps are desirable sites Tentative priority of Greenland sites (based on known surface conditions and availability of ancillary data) 1)  GISP2/GRIP (dry snow zone and substantial ancillary data)2)  NGRIP  (dry snow zone, wet bed in area, some ancillary data)3)  Camp Century (dry snow zone, some data available- 1966 borehole)4)  NEEM (most recent site, dry snow zone but ancillary data are difficult to retrieve so far)5)  Dye 3  (experiences surface melt but substantial ancillary data)Canadian Ice Caps as contingency:1)  Devon Island (ancillary data available, surface conditions need to be investigated, Canadian Cryovexvalidation site)2)  Agassiz Ice Cap (ancillary data available, surface conditions need to be investigated)

45. Greenland Deep and Intermediate Drill Sites/ Flight Trajectories Deep and Intermediate Boreholes Expected Flightline

46. Devon and Aggasiz Ice Cap Secondary Sites/ OIB Trajectories

47. Aircraft Update • Continued discussions with Ken Borek Air, Ltd. for use of Bassleraircraft • Bassler is desired given the extended range and familiarity of Borek Ltd with conducting US science projects in Greenland • Plans compatible with Bassler capabilities • Budget for 5 days/ 40 flight hours consistent with project plan • Accommodation of UWBRAD antenna appears straight forward Bassler Twin Otter

48. Other Possibilities • IFAC-CNR will deploy their radiometer from the tower at DOME-C again in November 2014-January 2015 • This deployment will complete the current IFAC project with ESA • Too soon for UWBRAD • IFAC proposed to ESA to deploy the system again November 2015-January 2016 • Potential to include UWBRAD tower deployment at DOME-C as part ofthe proposal • ESA project could cover transport costs for UWBRAD to Antarctica if UWBRAD were to arrive at IFAC by August 2015 • Would be desirable to include full 15 channel system, but even a 2 or 4 channel system could provide valuable information • Costs for project personnel support of this effort likely manageable within baseline budget since “ground based tests of 15 channel unit” are part of baseline project plan • Team will continue to seek opportunities for work in the Antarctic with NSF and NASA

49. Milestones and Timeline

50. Next 6 months • Project progressing according to schedule • No major risks identified • Differing TB profiles versus frequency in Greenland will continue to be focus on retrieval analyses • RFI processing algorithms will be focus of software development • Trade of “hybrid” vs. Dicke switching architecture continuing • Should be final before next review • No major impact on development schedule since majority of front end design is common to two approaches