Martin G. Mlynczak Climate Science Branch NASA Langley Research Center

1. SAO ASIC3 Workshop Far-Infrared Spectroscopy of the Troposphere FIRST Martin G. Mlynczak Climate Science Branch NASA Langley Research Center 16 May 2006

2. FIRST Team and Sponsors Technology Development and Flight Demonstration Team Marty Mlynczak NASA Langley Dave Johnson NASA Langley Charlie Hyde NASA Langley Stan Wellard Utah State/SDL Gail Bingham Utah State/SDL Mike Watson Utah State/SDL Harri Latvakoski Utah State/SDL Ken Jucks Smithsonian Astrophysical Observatory Wes Traub Smithsonian Astrophysical Observatory Jess Landeros JPL Jim Margitan JPL Bill Stepp & Team Columbia Scientific Balloon Facility Science Advisory Team Dave Kratz NASA Langley Ping Yang Texas A & M University Bill Smith U. Wisconsin Lou Smith NIA Paul Stackhouse NASA Langley Chris Mertens NASA Langley Bob Ellingson Florida State University Rolando Garcia NCAR ACD Bill Collins NCAR CGD Brian Soden GFDL John Harries Imperial College, London Rolando Rizzi U. Bologna, Italy Sponsors and Supporters NASA Earth Science Technology Office Ken Anderson George Komar Carl Wagenfuehrer Brian Killough (LaRC) NASA Science Mission Directorate Hal Maring Jack Kaye Mike Kurylo Don Anderson Phil DeCola

3. Far-Infrared Spectroscopy of the Troposphere Outline • Science Motivation and Justification for far-IR • FIRST Sensor Overview • FIRST Flight Summary and Performance Assessment • Future plans and directions to spaceflight • FORGE and RHUBC campaigns • FIDTAP • Summary

4. Far-Infrared Spectroscopy of the Troposphere A Brief History of Earth Radiation Budget Measurements ERB measurements from space first proposed by V. Suomi in late 1950’s First quantitative measurement of Earth System from space was ERB in late 1950’s, early 1960’s Measurement is of 2 “classic” energy flows: 1. Total Radiation = Emitted Thermal + Reflected Solar 2. Reflected Solar Radiation Emitted thermal radiation obtained by subtraction of classic energy flows In the past 40 years these measurements have been refined in terms of: 1. Improved spatial resolution 2. Improved calibration 3. Improved angular sampling Two critical dimensions remain – temporal (GERB) and spectral

5. Far-Infrared Spectroscopy of the Troposphere Far-IR Mid-IR

6. Far-Infrared Spectroscopy of the Troposphere Compelling Science and Applications of the Far-Infrared • Up to 50% of OLR (surface + atmosphere) is beyond 15.4 mm • Between 50% and 75% of the atmosphere OLR is beyond 15.4 mm • Basic greenhouse effect (~50%) occurs in the far-IR • Clear sky cooling of the free troposphere occurs in the far-IR • - Potential to derive atmospheric cooling rates directly from the radiances • Upper Tropospheric H2O radiative feedbacks occur in far-IR • Cirrus radiative forcing has a major component in the far-IR • Longwave cloud forcing in tropical deep convection occurs in the far-IR • Improved water vapor sensing is possible by combining the far-IR and standard mid-IR emission measurements Direct Observation of Key Atmospheric Thermodynamics

7. Far-Infrared Spectroscopy of the Troposphere Annual mean TOA fluxes for all sky conditions from the NCAR CAM Reference: Collins and Mlynczak, Fall AGU, 2001

8. Far-Infrared Spectroscopy of the Troposphere Annual mean TOA fluxes for clear-sky conditions from the NCAR CAM. Reference: Collins and Mlynczak, Fall AGU, 2001

9. Far-Infrared Spectroscopy of the Troposphere Clear-Sky Spectral Cooling Rate Far-IR Mid-IR

10. Far-Infrared Spectroscopy of the Troposphere Unobserved Observed Spectrally Integrated Cooling – Mid-IR vs. Far-IR

11. FIRST – Sensitivity to Cirrus Clouds Brightness temperature difference between two channels n1=250.0 cm-1 and n2=559.5 cm-1 as a function of effective particle size for four cirrus optical thicknesses FIRST spectra can be used to derive optical thickness of thin cirrus clouds (t < 2). Reference: Yang et al., JGR, 2003

12. Far-IR Measurements in our Solar System Nimbus III/IV, 1969/70 Hanel et al., 2003 Far – IR least measured from space on Earth!

13. FIRST System Performance Requirements • At present, no extant sensor in development for spaceflight with spectral sensing capability longer than 15 mm wavelength • FIRST developed technology needed to attain daily global coverage, from low-earth orbit, of the far-infrared spectrum (10 km IFOV from 900 km) • Spectral coverage: 10 to 100 mm (1000 to 100 cm-1) • Requires bilayer beamsplitter with > 92% efficiency 10-100 mm • Spectral Resolution: 0.625 cm-1 (unapodized), 0.8 cm OPD • Scan time 1.4 s • NEDT: 0.2 K (10 to 60 mm); 0.5 K (60 to 100 mm) • Optical throughput: • Sufficient to meet the NETD requirement for 100 fields in 1.4 s (10 x 10 array) • Technology to be demonstrated in space-like environment FIRST Developed under NASA’s Instrument Incubator Program (IIP)

14. FIRST Key Technology Requirements • Instrument Type: Fourier Transform Spectrometer • Gives greatest possible span of wavelengths in a single instrument • Beamsplitter: Germanium on polypropylene • Excellent response in far-IR, minimal absorption features • Detectors with kilohertz sampling frequencies • To record > 1000 samples in ~ 1 second from orbit • Single focal plane • To simplilfy the optical design and calibration • Complete system to be deployed on a high altitude balloon • To simulate the space environment

15. FIRST Interferometer Block Diagram Remote Alignment Tach/Torque motor Stationary mirror Beamsplitter Translating mirror Carriage Section Beam Splitter Section

16. FIRST Interferometer Cube and Mirror Drive Assembly Scene Radiance

17. FIRST Interferometer Cube

18. FIRST Broad Bandpass Beamsplitter 4 x RT Example FIRST beamsplitter performance curves FIRST beamsplitter in mounting ring at USU/SDL

19. Sample relative response curves (taken with SAO FIRS-2)

20. FIRST Focal Plane Layout Performance of Center (1, 10) and corner (4, 5) detectors will be used to demonstrate that FIRST has sufficient throughput to meet the NETD requirement for a 10 x 10 array

21. FIRST Balloon Payload System Interdewar Window Scatter Filter Polypropylene Vacuum Window Aft Optics Beamsplitter Scene Select Motor Interferometer Cube Remote Alignment Assembly Passive LN2 Heat Exchanger Active LN2 Heat Exchanger LN2 Volume Scene Select Mirror

22. In-flight Blackbody Space Earth FIRST Scene Select Assembly Mechanical Limit Switch (3) Scene Select Mirror Baffle Optical Encoder Scene Select Mirror Bearings Flex Coupling Stepper Motor

23. FIRST Balloon Payload System Interferometer Laser Box Sensor Dewar In-Flight Blackbody Dewar Interface Plate Plumbing / Vacuum Port Scene Select Assembly

24. FIRST – Calibration • FIRST designed with absolute calibration in mind, from the start • Instrument cooled to 180 K to simulate space environment and reduce instrument background • Full field external calibration sources • Multiple calibration sources (warm, cold) in laboratory • Multiple calibration sources in flight (warm, “space”) • Spectral range designed to cover 10 – 15 mm (+ far-IR) • Allows verification against “standard” instruments, e.g, AIRS, AERI, in mid-IR

25. Provide a cold source for calibration (<25K) Capable of operating while attached to any of the three scene select positions 2 hour hold time Silicon diode temperature detectors FIRST Space View Simulator LN2 Tank LHe Tank Specular Paint Diffuse Paint 77-95K Surface 6-12K Surface

26. FIRST 300K In-Flight Blackbody Cone Temperature Sensor Cylinder Heater Cone Heater G-10 Support / Thermal Leak Baffle Electrical Connectors MLI Blanketing

27. FIRST on the Flight Line June 7 2005

28. FIRST Flight Specifics • Launched on 11 M cu ft balloon June 7 2005 • Float altitude of 27 km • Recorded 5.5 hours of data • 1.2 km footprint of entire FPA; 0.2 km footprint per detector • 15,000 interferograms (total) recorded on 10 detectors • Overflight of AQUA at 2:25 pm local time – AIRS, CERES, MODIS • Essentially coincident footprints FIRST, AQUA instruments • FIRST met or exceeded technology development goals • FIRST, AIRS, CERES comparisons in window imply excellent calibration (better than 1 K agreement in skin temperature) FIRST records complete thermal emission spectrum of the Earth at high spatial and spectral resolution

29. window H2O O3 CO2 FIRST “First Light” Spectrum

30. FIRST Spectrum, Center Detector Mlynczak et al., GRL, 2006

31. FIRST Spectrum, Corner Detector Mlynczak et al., GRL, 2006

32. Comparison of AIRS, FIRST in Window Region Mlynczak et al., GRL, 2006

33. FIRST Spectra Compared with L-b-L SimulationDemonstration of FIRST Recovery of Spectral Structure Note: FIRST, LbL spectra offset by 0.05 radiance units

34. FIRST Measured, Calculated Radiance Mlynczak et al., GRL, 2006

35. FIRST Spectra Comparisons with L-B-L using AIRS Retrievals L-b-L does not yet include FIRST Instrument Response Functions

36. FIRST – Performance Assessment • Project finished on time and within budget • Spectra on Corner, Center detectors verify optical throughput requirement met (0.47 cm2 sr) • Spectral coverage (50 to 2000 cm-1) verify spectral response requirement exceeded • Calibration appears to be within 1-2 K of 3 NASA spaceflight sensors (MODIS, AIRS, CERES) – calibration met to first order • In-depth analysis of accuracy, precision, and noise underway • FIRST system now at TRL-6 and ready for science flights/campaigns

37. FIRST – Future Directions • Confirmation of far-IR calibration • RHUBC – Radiative Heating in Underexplored Bands Campaign • FORGE: Far-IR Observations of the Radiative Greenhouse Effect • Zenith view, ground based with multiple instruments • AERI, FIRST, TAFTS (UK) • Cold, dry conditions at altitude (few km) • See spectral development in far-IR to ~ 300 cm-1 • See blackbody spectrum at lower wavenumbers • Derive radiative cooling of mid-troposphere • Observe far-IR optical properties of cirrus in windows • Validate far-IR water vapor spectroscopy • Development of Far-IR Radiometric Standards • FIRST low-temp blackbodies • Detector development – FIDTAP – Achieve fast, broadband detectors capable of operation at temps > 10 K

38. FIRST Simulated Zenith Radiance

39. FIRST Simulated Zenith Radiance

40. FIRST – Status and Summary • FIRST successfully completed technology demonstration flight 6/2005 • Met or exceeded technology goals – now at TRL/6 • Combined “sounder” and “radiation budget” capabilities • Awaiting opportunity for spaceflight proposal • Continue to improve calibration and related technologies: • Develop improved radiometric standards • Compare extant far-IR spectral instruments • Develop remaining technology (detectors) • Validate cryo-cooler (> 10 K) technology for flight

41. FIRST Lands Safely after a Successful Flight

42. FIRST Bibliography Formal Publications • Mlynczak, M. G., D. G. Johnson, H. Latvakoski, K. Jucks, M. Watson, G. Bingham, D. P. Kratz, W. A. Traub, S. J. Wellard, and C. R. Hyde, First light from the Far-Infrared Spectroscopy of the Troposphere (FIRST) instrument, Geophys. Res. Lett., doi:10.1029/2005GL025114. Conference Proceedings and Presentations through Calendar Year 2005 • Mlynczak, M. G., D. G. Johnson, H. Latvakoski, K. Jucks, M. Watson, G. Bingham, W. Traub, S. Wellard, and C. R. Hyde, FIRST – Instrument description, performance, and results, Fall Meeting, American Geophysical Union, San Francisco, CA, paper IN13B-1084, 2005. • Liu, X., M. G. Mlynczak, D. G. Johnson, D. Kratz, H. Latvakoski, and G. Bingham, Atmospheric Remote Sensing using FIRST, World Scientific and Engineering Academy and Society (WSEAS) Meeting, Venice, Italy, 2005. • Bingham, G.E., H. Latvakoski, S. Wellard, D. Garlick, M. Mlynczak, D. Johnson, W. Traub, K. Jucks. 2005. Far-infrared spectroscopy of the troposphere (FIRST): sensor calibration performance. International Symposium on Remote Sensing of Environment. St. Petersburg, RU. June 20 – 24, 2005. • M. G. Mlynczak, D. G. Johnson, G. E. Bingham, K. W. Jucks, W. A. Traub, L. Gordley, P. Yang, The far-infrared spectroscopy of the troposphere project, SPIE Fourth International Asia-Pacific Environmental Remote Sensing Symposium, Honolulu, HI, 2004. • Kratz, D. P., Mlynczak, M. G., Johnson, D. G., Bingham, G. P., Traub, W. A., Jucks, K., Hyde, C. R., Wellard, S., FIRST, The Far-Infrared Spectroscopy of the Troposphere Project, Fall AGU Meeting, San Francisco, CA Paper SF43A-0782, 2004.

43. FIRST Bibliography • G. E. Bingham, Harri M. Latvakoski, Stanley J. Wellard, MartinG. Mlynczak, David G. Johnson, Wesley A. Traub, and Kenneth W. Jucks, Far-infrared spectroscopy of the troposphere (FIRST): sensor calibration performance. SPIE Fourth International Asia-Pacific Environmental Remote Sensing Symposium. Multispectral and Hyperspectral Remote Sensing Instruments and Applications II. Paper 5655-25. Honolulu, HI, USA, 2004. • Bingham, G.E.,, H.M. Latvakoski, S.J. Wellard, M.G. Mlynczak, D.G. Johnson, W.A. Traub, and K.W. Jucks, Far-infrared spectroscopy of the troposphere (FIRST): sensor development and performance drivers. Optical Spectroscopic Techniques and Instrumentation for Atmospheric and Space Research V. International Symposium on Optical Science and Technology, SPIE, v. 5157, San Diego, CA. August 7-8, 2003. • Mlynczak, M., D. Johnson, G. Bingham, K. Jucks, W. Traub, L. Gordley, and J. Harries, The far-infrared spectroscopy of the troposphere (FIRST) project, IGARSS 2003, Toulouse, France. Invited, July 2003. • Bingham, G.E., and H. M. Latvakoski, Far Infrared Technology Development for Space Surveillance, Space Based EO/IR Surveillance Technology Conference Kirtland Air Force Base, Albuquerque, NM. May 13-15, 2003. • Bingham, G.E., S.J. Wellard, M.G. Mlynczak, D.G. Johnson, W.A. Traub, and K.W. Jucks, Far InfraRed Spectroscopy of the Troposphere (FIRST): Sensor Concept, Asia-Pacific SPIE 02, Hangzhou, China, Paper 4897-23, 2002. • Mlynczak, M. G., D. Johnson, E. Kist, D. Kratz, C. Mertens, and W. Collins, Far-Infrared Spectroscopy of the Troposphere, Fall Meeting, American Geophysical Union, San Francisco, December 2001. • Collins, W. D., and M. G. Mlynczak, Prospects for measurement of far-infrared tropospheric spectra: Implications for climate modeling, Fall Meeting, American Geophysical Union, San Francisco, December, 2001.

44. FIRST Bibliography • Mlynczak, M. G., J.E. Harries, R. Rizzi, P. W. Stackhouse, D. P. Kratz, D. G. Johnson, C. J. Mertens, R. R. Garcia, and B. Soden, The far-infrared: A frontier in remote sensing of Earth’s climate and energy balance, in Optical Spectroscopic Techniques, Remote Sensing, and Instrumentation for Atmospheric and Space Research IV, Allen M. Larar and Martin G. Mlynczak, Editors, Proceedings of SPIE, Vol 4485, 150-158, 2001. • Mertens, C. J., Feasibility of retrieving upper tropospheric water vapor from observations of far-infrared radiation, in Optical Spectroscopic Techniques, Remote Sensing, and Instrumentation for Atmospheric and Space Research IV, Allen M. Larar and Martin G. Mlynczak, Editors, Proceedings of SPIE, Vol 4485, 191-201, 2001. • Kratz, D. P., High resolution modeling of the far-infrared, in Optical Spectroscopic Techniques, Remote Sensing, and Instrumentation for Atmospheric and Space Research IV, Allen M. Larar and Martin G. Mlynczak, Editors, Proceedings of SPIE, Vol 4485, 171-180, 2001. • Johnson, D. G., Design of a far-infrared spectrometer for atmospheric thermal emission measurements, in Optical Spectroscopic Techniques, Remote Sensing, and Instrumentation for Atmospheric and Space Research IV, Allen M. Larar and Martin G. Mlynczak, Editors, Proceedings of SPIE, Vol 4485, 220-224, 2001.