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IGARSS_Brown_Aquarius_2011.pptx
IGARSS_Brown_Aquarius_2011.pptx
IGARSS_Brown_Aquarius_2011.pptx
IGARSS_Brown_Aquarius_2011.pptx
IGARSS_Brown_Aquarius_2011.pptx
IGARSS_Brown_Aquarius_2011.pptx
IGARSS_Brown_Aquarius_2011.pptx
IGARSS_Brown_Aquarius_2011.pptx
IGARSS_Brown_Aquarius_2011.pptx
IGARSS_Brown_Aquarius_2011.pptx
IGARSS_Brown_Aquarius_2011.pptx
IGARSS_Brown_Aquarius_2011.pptx
IGARSS_Brown_Aquarius_2011.pptx
IGARSS_Brown_Aquarius_2011.pptx
IGARSS_Brown_Aquarius_2011.pptx
IGARSS_Brown_Aquarius_2011.pptx
IGARSS_Brown_Aquarius_2011.pptx
IGARSS_Brown_Aquarius_2011.pptx
IGARSS_Brown_Aquarius_2011.pptx
IGARSS_Brown_Aquarius_2011.pptx
IGARSS_Brown_Aquarius_2011.pptx
IGARSS_Brown_Aquarius_2011.pptx
IGARSS_Brown_Aquarius_2011.pptx
IGARSS_Brown_Aquarius_2011.pptx
IGARSS_Brown_Aquarius_2011.pptx
IGARSS_Brown_Aquarius_2011.pptx
IGARSS_Brown_Aquarius_2011.pptx
IGARSS_Brown_Aquarius_2011.pptx
IGARSS_Brown_Aquarius_2011.pptx
IGARSS_Brown_Aquarius_2011.pptx
IGARSS_Brown_Aquarius_2011.pptx
IGARSS_Brown_Aquarius_2011.pptx
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IGARSS_Brown_Aquarius_2011.pptx

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  • 1. Development of a L-band On-orbit Calibration Reference Model for the Marie-Byrd Antarctic Region:
    Application to Aquarius, SMOS and SMAP
    Shannon Brown and Sidharth Misra
    Jet Propulsion Laboratory, California Institute of Technology
  • 2. L-band Radiometer Calibration
    Calibration at L-band has become an important issue: SMOS, Aquarius, SMAP
    These radiometers use an internal calibration approach; internal switches and noise diodes
    Requires external end-to-end calibration reference – pre-launch and on-orbit
    Calibration techniques developed for radiometers on-board satellite altimeter missions applicable
    Altimeter radiometers also employ internal calibration
    For Jason series radiometers, calibration referenced to stable on-Earth references
    2
  • 3. TBReferences 18-37 GHz
    Tune TB to hot and cold absolute brightness temperature references
    Vicarious Cold Reference (Ruf, 2000, TGARS)
    Stable, statistical lower bound on ocean surface brightness temperature
    Amazon pseudo-blackbody regions (18-40 GHz) (Brown and Ruf, 2005, JTECH)
    THOT(frequency, incidence angle, Local Time, Time of year)
    SSM/I 37.0 GHz V-pol – H-pol TB
    • Techniques recently used to generate 13-year climate data record from Topex radiometer data (Brown et al. 2009, JTECH)
    • 4. Used on-Earth references to remove long-term drift, instrument temperature dependence and antenna pattern correction errors
    Hot Reference Targets
  • 5. AMSR-E De-polarization
    Developing On-Earth TB Calibration References at L-band
    Natural targets for L-band radiometer calibration over on-Earth dynamic range
    Calm, flat ocean scenes – Cold reference
    Ice sheets: Antarctica (e.g. Dome-C), Greenland – Mid-range reference
    Land areas: flat, dry deserts; homogeneous heavily vegetated regions – Hot reference
    Use to assess absolute calibration, monitor stability and assess residual instrument calibration errors
    37 V-H
    23 V-H
    18 V-H
    10 V-H
    6 V-H
  • 6. Use match-ups between Aquarius and ocean altimeters to identify observations over calm seas
    Compare Aquarius to modeled TB
    Calm ocean surface reduces model uncertainty – nearly specular emission
    Model inputs (e.g. SST, SSS) from ancillary data sources
    Sort comparisons to identify residual errors in corrections (e.g. solar, galactic, ionosphere)
    Significant number of match-ups with minimal temporal and spatial difference (1 hr/100km)
    5
    Cold TB Reference
    Number of match-ups per 1o bin – all horns
  • 7. Cold Scene Stability Monitoring
    Used simulated data to assess resolution of method
    Compare TBs to model to look for jumps/drifts
    6
    TBV – Model : Horn 1
    Inter-channel double difference : Horn 1
    Over range of 0 < WS < 5 m/s
    Assumes 0.5C SST knowledge and 0.5psu SSS knowledge
  • 8. Antarctic Calibration Reference
    Recent work has shown Dome-C as suitable candidate for an on-Earth L-band reference (Floury et al., 2002; Macelloni et al. 2006 ; Macelloni et al. 2007)
    Region is heavily instrumented and studied, but small in size
    Particularly for Aquarius, larger site desired due to fixed independent radiometer beams
    Used AMSR-E to search for other suitable Antarctic calibration sites
    Identified other regions with low spatial and temporal variability of surface and deep ice temperature
    Aquarius 3-beams
  • 9. Temporal stability at 6 and 37 GHz
    6.9 GHz
    37 GHz
    • Regions below 0.5K std.dev chosen for 6GHz
    • 10. Regions below 4K std.dev chosen for 37GHz
    • 11. Spatial stability of region evaluated by searching for contiguous thermally stable sets within a 150km radius
  • Marie Byrd Region:
    • Marie-Byrd region identified as suitable site
    • 12. Approximate area of stable region ~160,000km2
    • 13. Two automated weather stations (AWS) in region
  • Characteristics of Marie-Byrd Region
    10
    Accumulation in Marie-Byrd region ~30cm/yr, higher than in East Antarctica
    Gentle upward slope from north to south across the region
    Surface density ~350kg/m-3 with firn-ice transition around 64 m (Gow 1968)
    Accumulation Rate
    Rubin and Giovinetto 1962
    Cuffey and Patterson 2010
  • 14. Characteristics of Marie-Byrd Region
    Warmer surface temperatures in Marie-Byrd region than East Antarctica
    11
    Mean Surface Temperature
    Cosimo2000
  • 15. 12
    6.9 GHz H-pol
    37 GHz H-pol
    6.9 GHz V-pol
    37 GHz V-pol
  • 16. 13
    37 GHz H-pol
    6.9 GHz H-pol
    37 GHz V-pol
    6.9 GHz V-pol
  • 17. Marie-Byrd vs. Dome C
    Marie-Byrd
    Dome-C
    Tb37_pp = 30K
    1Macelloni (2007)
    Tb37_pp = 15K
  • 18. 15
    AMSR-E V-pol Dome C
    AMSR-E V-pol MB
    AMSR-E H-pol Dome C
    AMSR-E H-pol MB
  • 19. `
    16
    AMSR-E 6 GHz H-pol
    AMSR-E 6 GHz V-pol
    AMSR-E 37 GHz H-pol
    AMSR-E 37 GHz V-pol
  • 20. Long Term Temperature Stability at Marie-Byrd
    • AMSR-E 6 GHz TB stable to ~0.2K from 2003 to 2011
    • 21. 6 GHz TB stable to <0.1K over last 5 years
    Annual averaged surface temperature from Byrd AWS stable to ~1C from 1980 – 2000
    17
  • 22. Development of Coupled Forward Model
    Use model to transfer calibration from higher frequencies radiometers to L-band
    Model couples an ice heat-transport equation and radiative-transfer equation
    Constrain model using AMSR-E and in situ AWS data
    constrain density profile, temperature profile and grain size
    Predicts brightness temperature at L-band
    Use as a calibration reference
    • Tracking calibration stability over time
    • 23. Sensitive to heat-transport model, but temporal variability small
    • 24. Lower uncertainty on monthly or longer time scales
    • 25. Inter-satellite calibration
    • 26. Use region to assess calibration between sensors – daily observations
    • 27. Model used to account for differences in incidence angle
    • 28. Assessing absolute calibration
    • 29. Uncertainty dependent on radiative transfer model
    • 30. Evaluate several models to estimate uncertainty
  • Surface temperature values obtained from AWS stations used as top boundary condition, with its mean as the bottom boundary condition
    Only considered annual harmonic
    Used simple radiative transfer model assuming layered ice to estimate L-band and C-band V-pol TB annual signal
    summer
    winter
    autumn
    spring
  • 31. 20
    6.9 GHz H-pol
    SMOS 55o H-pol
    df
    SMOS 55o V-pol
    6.9 GHz V-pol
  • 32. Time Series Comparison
    Monthly averaged SMOS TB at 55o incidence angle compared to AMSR-E 6.9 GHz channel for June 2010 to June 2011
    Observed annual signal at L-band higher than expected
    21
    AMSR-E 6.9 GHz and SMOS V-pol
    AMSR-E 6.9 GHz and SMOS H-pol
  • 33. Conclusions and Future Work
    Marie-Byrd region identified as a candidate L-band calibration site in West Antarctica
    Large in extent, thermally stable
    Complementary to Dome-C site
    Analysis of AMSR-E indicates good long term stability of region
    Developing model to transfer calibration from higher frequency radiometers (e.g. AMSR-E, WindSat) to L-band over region
    Next steps
    Evaluate several radiative transfer models, constrain using AMSR-E
    Inter-compare Aquarius and SMOS over region
  • 34. backup
    23
  • 35. TB References
    Tune TB to hot and cold absolute brightness temperature references
    Vicarious Cold Reference (Ruf, 2000, TGARS)
    Stable, statistical lower bound on ocean surface brightness temperature
    Amazon pseudo-blackbody regions (18-40 GHz) (Brown and Ruf, 2005, JTECH)
    THOT(frequency, incidence angle, Local Time, Time of year)
    • Sample references over various instrument temperature states
    • 36. Multiple independent estimates
    • 37. Additionally, constrain solution to minimize slope of RMS error vs. instrument temperature
    SSM/I 37.0 GHz V-pol – H-pol TB
    Hot Reference Targets
  • 38. Salinity Retrieval Validation
    Form database of Aquarius co-locations with in situ data
    Argo float array, the Shipboard Sensor Database (SSD) and the Global Temperature-Salinity Profile Program (GTSPP).
    Analyze global mean differences between Aquarius retrieved salinity and in-situ measurements
    Assess over time and instrument temperature
    Analyze regional differences
    Assess antenna pattern correction, faraday rotation correction and atmospheric and roughness corrections
    25
  • 39. Faraday Rotation Correction
    Dual-frequency altimeter match-ups also useful for assessing Faraday rotation correction
    Match-ups cover large range of TEC values
    26
  • 40. 27
  • 41. Aquarius orbit overlap
  • 42. Calibration Approach for Aquarius
    Monitor instrument level parameters and diagnostics
    Objective is to identify the cause of any observed calibration or retrieval error or instability in order to apply a suitable correction at the appropriate level of processing
    Compare retrievals to in situ ground truth or models
    Compare brightness temperatures to natural on-Earth reference targets
  • 43. AMSR-E vs AWS: Yearly Temperatures (2008)
    • Data curve fit to the following equation, with a period of 365 days
  • Annual Temperature Variations
    Annual amplitude decreases and phase lag increases with decreasing frequency
    Penetration depth near 10 m at 6 GHz
    Nearly 50 m at 1.4 GHz
  • 44. Radiative Transfer Model
    Used simple radiative transfer model to estimate L-band TB from estimated temperature vs depth
    Snow is assumed to be dry and pure
    Density was varied from 0.3g/cm3 to 0.916 g/cm3 to fit with AMSR-E values
    Simple empirical scattering correction
    0.17 K peak to peak
    1.4 GHz
    6.8 GHz
    10.7 GHz
    18.7 GHz
    36.5 GHz

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