May 23, 2003

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Hyperspectral Data Compression Workshop
Spectral Considerations for the Measurement of
Carbon
Janette C. Gervin, Robert G. Knox, Elizabeth M.
Middleton, Antonio Mannino, Watson W.
Gregg, Charles R. McClain, Forrest G. Hall, and
Jaime Esper NASA Goddard Space Flight
Center Greenbelt, MD 20771

May 23, 2003
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Greenhouse Gases and Warming

• Weather station records and ship-based
  observations indicate that global mean surface
  air temperature warmed between about 0.4 and 0.8
  o C (0.7 and 1.5 o F) during the 20th century.

• A major contributor to climate warming is the
  steady increase in atmospheric greenhouse gases.

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Uncertain Futures
As CO2 emissions have increased, the land and
oceans have absorbed more and more carbon.
Projections of future CO2 levels depend on our
knowledge of the biosphere and how it interacts
with climate Given identical human emissions,
different models project dramatically different
futures. Which is correct? How can we know?
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GCCP Technology Activities Roadmap
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Project Description Global Carbon Cycle Plan

• Mission Objective multi-year mission to
  determine the Geographic Distribution and the
  Seasonal and Interannual Variation of Global
  Carbon Exchange between the Earths Atmosphere,
  its Land Masses and Oceans to determine the
  Effect of Climate Variation and Secular Trends on
  the Geographic and Temporal Dynamics of the
  Global Carbon Cycle and to provide Information
  Supportive of Policy Decisions and Mitigation
  Approaches
• Organizations Lead Goddard Space Flight Center
  designated lead by HQ Partners Other NASA
  Centers, other federal agencies, and university
  scientists
• Mission Description Five to seven missions in
  (primarily) sun-synchronous orbits measure
  atmospheric carbon dioxide, aerosols, ocean and
  coastal carbon productivity, and low and high
  density land biomass.
• Launch To be launched on two-year centers
  starting in 2008
• Pathfinder CO2 Ocean Carbon Low Density
  Biomass High Density Biomass Advanced CO2

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Table 1 Assumed measurement requirements  
Assumed Measurement Requirements (2001)
  Note Sun synchronous (unless otherwise
stated), low earth orbits, and mission duration
of at least 3 years (technology permitting),
assumed.
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Nominal Set of GCCP Missions
Pathfinder CO2
Description A small satellite mission that makes
high-precision (1 to 2 ppmv) global measurements
of atmospheric column CO2 abundance
Advanced CO2
Ocean Carbon
Low Density Biomass Coastal Ocean
High Density Biomass
Description A satellite mission that provides
improved regional and global estimates of
vegetation biomass and carbon stocks, studies the
response of terrestrial ecosystems to major
disturbances, and measures the rate of recovery
Description A small satellite mission that makes
those ocean color measurements critical to the
determination of ocean biomass, primary
productivity, and dissolved organic matter
Description A small satellite mission that
measures the global concentration of carbon
dioxide and oxygen in the lower troposphere
Description A satellite mission that provides a
synoptic view of the Earths ecosystems, their
spatial distribution, and temporal dynamics with
global measurements of land cover, land cover
change, and ocean surface chlorophyll
Instrument A passive spectrometer with a 10 km
spatial resolution that provides high
signal-to-noise ratio detection of atmospheric
CO2 and O2 during the day time portion of the
orbit
Instruments A pulsed, dual frequency, tunable
laser sounder operating in the 1570 nm band for
carbon dioxide detection and in the 770 nm band
for oxygen detection, coupled with a lightweight
passive spectrometer for measuring absorption of
reflected sunlight in the same spectral regions
Instrument A scanning telescope equipped with an
on-board solar calibrator that makes irradiance
measurements in 10 spectral bands from the
ultraviolet to the near infrared additional
bands or complementary hyper-spectral instrument
to obtain coastal ocean data
Instrument A hyperspectral imager providing high
signal-to-noise ratios and covering a frequency
range from 450 to 2350 nm with a SWIR bandwidth
of 10 nm and a VNIR bandwidth of 5 nm
Instruments A P-band SAR operating at 0.44 GHz
and a multi-track, 1.064 micron, imaging laser
altimeter with a capability of resolving 0.5 m
differences in vegetation height
Mission Life 3-5 years Orbit Sun synchronous,
705 km for passive inst., 400-590 km for
lidars Spacecraft Small, low- cost, three-axis
stabilized, nadir pointing
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Ocean Carbon

• Description A small satellite mission that makes
  those ocean color measurements critical to the
  determination of ocean biomass, primary
  productivity, and dissolved organic matter
• Instrument A rotating, scanning telescope
  equipped with an on-board solar calibrator that
  makes irradiance measurements in 10 spectral
  bands from the ultraviolet to the near infrared
  additional bands or complementary hyperspectral
  instrument to obtain coastal ocean data
• Spacecraft A small, low-cost, three-axis
  stabilized, nadir pointing spacecraft from the
  RSDO catalog with a propulsion system for orbit
  raising, maintenance, and maneuvers

Launch Date FY 2010 Mission Life 5 Years Orbit
705 km polar, sun-synchronous, with a 1200 noon
crossing time Space Access Pegasus XL or
equivalent class launch vehicle Mission Options
A single instrument mission
Key Technologies selection of bands not
generally used in land applications, improvements
in sensor design, and the use of onboard data
processing to optimize data retrieval
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Low Density Biomass/Coastal Ocean

• Description A satellite mission that provides a
  synoptic view of the Earths ecosystems, their
  spatial distribution, and temporal dynamics with
  global measurements of land cover, land cover
  change, and ocean surface chlorophyll
• Instrument A hyperspectral imager providing high
  signal-to-noise ratios and covering a frequency
  range from 450 to 2350 nm with a SWIR bandwidth
  of 10 nm and a VNIR bandwidth of 5 nm
• Spacecraft A low-cost, three-axis stabilized,
  nadir pointing spacecraft from the RSDO catalog
  with a propulsion system sized to allow formation
  flying with other land imaging platforms

Launch Date FY 2012 Mission Life5 Years Orbit
705 km circular sun-synchronous with a 1030 a.m.
descending node Space Access Taurus or
equivalent class launch vehicle
Key Technologies Large area focal plane arrays,
large capacity on-board recorders, and high rate
downlink systems for improved mission performance


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Coastal Ocean Bands
Coastal Ocean band width center (nm) 360 10 380 1
0 412 10 443 10 490 10 510 10 555 10 660 10 670 10
680 10
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Low Density Biomass Bands
Terrestrial Biomass band width center (nm) 531 6
570 3 665 10 680 5 697.5 2 750 5 780 10
Band positions plotted over 6S modeled nadir
reflectance from a vegetated pixel, using a US
standard atmosphere (1962) and continental-type
aerosols. Top-of-atmosphere reflectance direct
beam is the signal from the land-surface pixel -
attenuated by absorption and scattering, total
includes path radiance from molecular scattering
and aerosols.
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Atmospheric Transmission
.Atmospheric transmission after 2-way gaseous
line absorption by H2O and O2, calculated from
the HITRAN 2000 database, using the GENSPECT
Matlab toolbox. (Water vapor mixing ratios from
1976 U.S. standard atmosphere.) UV and visible
wavelengths are also attenuated by broad ozone
features (not shown).
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A Fork in the Road

• Narrow Bands in atmospheric windows, with
  broadband
• aerosol/atmospheric correction
• (e.g., MODIS surface reflectance products)
• Hyperspectral with enough fidelity to both
• -do atmospheric correction and
• -resolve vegetation spectral features
• (e.g., derivative spectra)

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Ongoing GSFC Study of a Combined GEO
Hyperspectral Mission

• Address the original science requirements, while
  increasing the scientific return of a single
  spacecraft
• Renewed interest in advanced measurement
  capabilities from geostationary altitudes,
  particularly hyperspectral measurements.
• New emphasis on light-use efficiency and
  ecosystem carbon exchange
• Full diurnal coverage, hemispheric or near-global
• Single spacecraft, near geostationary, or LEO
  constellation

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Instrument Performance

• 1.2-meter aperture required for 100-meter
  resolution diffraction limited performance.
• 340nm to 1000nm, and 1000nm to 2400nm grating
  spectrometers.
• Silicon CCDs or Photodiode arrays used for the
  visible and near Infrared channels, and Mercury
  Cadmium Telluride detectors used for the Short
  Wave Infrared Channels.
• Scan perpendicular to the spatial direction, and
  parallel to the spectral direction on the
  detector.
• Size 1.3 x 1.3 x 2.5 meters, mass 1000 Kg,
  with adequate contingency. Power 350 watts,
  including thermal control.

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SNR Performance

• Effective resolution constrained by SNR
  requirements 10001
• A 4-degree per minute scan rate results in one
  full Earth-scan every 3 hrs

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Conclusions

• Preliminary study demonstrates both advantages
  and challenges of a GEO hyperspectral platform.
• Advantages are full diurnal hemispheric coverage
  of the Earth, or near-global coverage at a
  minimum rate of once every two days, all
  achievable with a single spacecraft.
• The challenge still remains to obtain desired
  high spatial and spectral resolution
  hyperspectral images with high SNR .
• EO-1 technology pathfinder
• EO-1 Hyperion data valuable for requirements
  studies and testing algorithms