Infrared Remote Sounding of the Earth's atmosphere with AIRS

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Infrared Remote Sounding of theEarth's
atmosphere with AIRS

• Atmospheric Spectroscopy Laboratory
• L. Larrabee Strow
• Sergio DeSouza-Machado
• Scott Hannon
• Howard Motteler
• Ji Gou
• Yvonne Edmonds (now at Stanford Univ.)
• Simon Carn (JCET)
• Seminars, week of Oct 18, 2004

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Overview

• Emphasis on climate applications
• AIRS developed primarily for weather forecasting
• 1st new weather satellite technology in 20 years
• AIRS instrument the first hyper(ultra?)spectral
  sounder
• Physics of the instrument
• Radiative transfer
• Good enough for climate?
• Validation
• Climate parameters
• Temperature
• Humidity
• Clouds
• Carbon Dioxide
• Carbon Monoxide
• Methane
• Sulpher Dioxide
• Aerosols (dust, ash)
• Cirrus clouds

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Climate Monitoring with Weather Satellites

• One thermometer, humidity sensor for the globe
• Weather satellites require dense coverage
  ??expensive sensor with high throughput
• If hyperspectral weather satellites are well
  calibrated, and intercompared will they be
  accurate enough? (Big savings.)
• Problems doing climate with weather satellites
• Calibration very expensive
• Validation what is truth?
• U.S. and Europe now providing different
  hyperspectral sounders in different orbits
• Large data volumes make reprocessing expensive
• Advantages of weather satellites
• Weather satellites appear to be here to stay
• Calibration by sensor vendors is improving
• Technologies are frozen for 15 years at a time
  (part of being expensive)

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Radiation from Sun to Earth
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Climate Model Uncertainties
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Knowledge of Radiative Forcings
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AIRS vs Blackbody Radiances

• Black 300K Red Sept. 2003 mean
  radiance, 0 to -10 deg. Lat.
• Green 270K Blue Sept. 2003 mean
  radiance, -40 to -50 deg. Lat.
• Magenta 220K

300K
300K
270K
270K
220K
220K
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An AIRS Spectrum
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Radiative Transfer Equation
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Why AIRS Needs to Last Beyond 2009
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AIRS on AQUA at TRW
IASI on METOP at Alcatel
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EOS Aqua was launch on 4 May 2002 into a 705km
altitude sun-synchronous orbit. AIRS IR
calibration started on 13 June 2002 Routine
operations started 1 September 2002 Expected end
of life 2009
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Atmospheric Spectroscopy Lab Computers
100 cpus, Linux OS Gigabit backbone network 20
Tbytes On-Line 22 Tbytes On Tape (soon) Ingest
33 Gbytes/day On-line database of AIRS clear
FOVS (0.7 Tbytes)
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AIRS-AMSU-HSB SCIENCE TEAM
Dr. Mous Chahine NASA/JPL Dr. George
Aumann NASA/JPL Dr. Roberto Calheiros
INPE/BSA, Brazil Dr. Alain Chedin CNRS,
France Dr. Catherine Gautier UC Santa
Barbara Dr. Mitch Goldberg NOAA/NESDIS Dr.
Eugenia Kalnay U of Maryland, College
Park Dr. John Le Marshall Bureau of
Meteorology, Australia Dr. Larry McMillin
NOAA/NESDIS Dr. Rolando Rizzi University of
Bologna, Italy Dr. Hank Revercomb
University of Wisconsin Dr. Philip Rosenkrans
MIT Dr. William Smith NASA/LaRC Dr.
David Staelin MIT Dr. Larrabee Strow
U of Maryland, Baltimore County Dr. Joel
Susskind NASA/GSFC
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Instrument Parameters

• Grating spectrometer
• ?/? ? 1200
• ? 3.7 15.4 microns, ? 650 2700 cm-1
• 13 lines/mm grating, using order 3-11
• Spectrometer cooled to 155K
• HgCdTe detectors (4482 of them) cooled to 58K
• - 49.5 degree ground swath
• FOV is 13.5 km from 705.3 km orbit
• Calibration with space, blackbody views every
  2.67 sec (scan cycle)
• Each 2378 channel spectrum taken in 22.4 msec
• 30 spectra a second!
• 30 Gbytes/day (stored next door)
• 22 Tbytes of data over 2 years (8TB on-line, 0.5
  Tbyte clear)
• 4 visible channels with 2.3km footprint

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AIRS Optics
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AIRS Ray Trace
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Focal Plane Map
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An AIRS Spectrum(Color Coded by Focal Plane
Array)
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Ready for Integration on AQUA
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IVAN
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AIRS Viz Image of Ivan
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Stability of AIRS Radiometry

• Clear FOVS, ocean only
• Compare observed 2616 cm-1 radiance to
  computed radiance using NOAA RTG-SST product
• RTA-SST tied to bulk SST measured by large
  network of tropical buoys

Slope is 0.008 K/year, so no measurable
radiometric drift Offset due to day/night
aliasing and evaporative cooling of skin This
result is key to using AIRS for climate studies
at other frequencies sensitive to air
temperature, water abundance, and minor gases.
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Stability of AIRS Frequencies

• Need frequency stability for climate studies as
  well
• AIRS exhibits seasonal frequency cycle,
  peak-to-peak is 0.4 of SRF width!
• Superimposed on seasonal cycle is a smooth drift
  of 0.1-0.3 of SRF width per year.
• Seasonal cycle equiv. to 0.7ppm CO2 (out of 0-6
  ppm variability)
• Long term drift (0.2) equiv. to 0.3 ppm of CO2
  (out of 3 ppm per year)

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Minor Gas Retrievals with Airs
AIRS was not designed to measure minor gases
except for O3

• CO2 Monthly zonal averages, soon will have a
  2-year record (clear,ocean only)
• CH4 Global 2 degree maps zonal averages
  (clear, ocean only)
• SO2 Case studies (about 8 eruptions studied so
  far), no monitoring
• CO Large scale retrievals using C. Barnets
  AIRS science code in addition to monthly
  averages. Land and ocean, uses cloud-cleared
  radiances.

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CO2 Detection with AIRS

• The AIRS dataset used here is a clear-only, ocean
  set of FOVs that are subsetted at UMBC from the
  L1b data.
• These data are averaged on a 2 by 2 degree
  lat/long grid.
• Most work done with the 792 cm-1 channel, some
  with the 2390 cm-1 channel.
• The minor gas amounts are computed by shifting
  the CO2 profile until the brightness temperature
  bias is zero for the particular channel sensitive
  to CO2.
• Use ECMWF T(z) and H2O(z) (adjusted for observed
  total column water)
• Fit for effective SST
• Kernel function peaks around 500 mbar, little
  sensitivity in boundary layer (why you need OCO).
• We have also derived mean monthly CO and CH4
  amounts with this same technique.
• Most of the results here use zonal averages
  derived from a 2 x 2 degree monthly average
  lat/lon grid.

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AIRS Jacobians for Minor Gases
CO_2 measurement done with 792 cm-1
channel. Planck T-dependence almost cancels
Boltzmann T-dependence
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Aug. 2002 April 2003 CO2 Monthly Zonal
AveragesUsing the 792 cm-1 Channel
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Zonally Averaged CO2 Variability with Time
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Fit of 20 months to sinusoidal function(secular
trend previously determined)

• CO2 a bsin(2?t/12 c)
• t time in months

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Zonally Averaged CO2 Variability with Time
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20 Months of Zonally Averaged CO2791.75 cm-1
Channel
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20 Months of Zonally Averaged CO22390.11 cm-1
Channel
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AIRS Global Mean CO2Weighted by cos(LAT)
Estimated bias is 5ppm ( 0.17K) based on
NOAA-CMDL global mean for 2003.
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Comparison of CO2 Using Different Channels(2390
cm-1 bias was scaled to equal mean value of 792
cm-1 bias)
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NOAA CMDL vs AIRS for Dec. 2002(CMDL has not
made these data available for 2003 as yet.)
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VERY Preliminary CO2 Map for May 2003
Obs ppm - 370
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CO2 Future Work

• Extend to land
• Improve S/N with more channels (better spectral
  cal of 4.3 micron channels will make this
  possible)
• Can T(z) and CO2 be retrieved simultaneously w/o
  ECMWF?
• Monthly averaging probably hides traces of
  source/sinks?
• IR radiances contain lots of interesting climate
  signatures!

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CO Retrievals from AIRS Radiances

• CO retrieval part of standard T(p), Q(p)
  retrieval, implemented in Chris Barnets science
  code running on our Linux cluster at UMBC.
• Retrieves CO column that nominally peaks 500
  mbar, very little boundary layer sensitivity.
• Sept. 2002 global retrievals
• INTEX support real-time retrievals of CO to
  aid aircraft flight-lines during INTEX. Data
  analyzed less than 24 hours after being recorded.
  (Thanks to Mitch Goldberg and Walter Wolf for
  providing AIRS data from their real-time feed.)
• AIRS NOT optimized for CO only a few CO lines
  are recorded.
• Validation with in-situ sensors and MOPITT
  suggest 15 column accuracies.

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CO in AIRS Spectra
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• 500

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AIRS
MOPITT
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• 80 of the planet seen each day, peak
  sensitivity 500mb
• preliminary validation says good to 15 at
  500mb

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AIRS
fires
Asian pollution
USA pollution
MOPITT

• Standard retrievals on AMSU footprint, binned to
  a 1 degree grid
• preliminary validation says good to 15 at 500mb

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Methane from AIRS

• 19 months of methane column in the 200-700 mbar
  range
• ECMWF Used for atmospheric temperature and
  humidity
• Monthly averages over ocean using clear FOVs
• Scale is in change in methane from reference
  value
• ALL RESULTS SHOWN HERE ARE PRELIMINARY!

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Zonal Averages of Methane19-month record (Sept.
2002 March 2004) Constant biased to North.
Hemis. winter
? CH4 a bsin(2pi? t/12 c), ? t month
index
Fit assumed no secular trend!
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09/2002 vs 09/2003
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11/2002 vs 11/2003
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01/2003 vs 01/2004
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03/2003 vs 03/2004
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Separation of Dust from Cirrus
Imaginary Index of Refraction of Ice and Dust

• Both ice and silicate absorption small in 1200
  cm-1 window
• In the 800-1000 cm-1 atmospheric window
• Silicate index increases
• Ice index decreases
• with wavenumber

Volz, F.E. Infrared optical constant of
ammonium sulphate, Sahara Dust, volcanic pumice
and flash, Appl Opt 12 564-658 (1973)
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Silicate (ash cloud) Detection at Anatahan
Image is ECMWF bias difference of 1227 cm-1 984
cm-1
Note slope
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Cirrus Detection at Anatahan
Image is bias ECMWF bias difference of 1227 cm-1
781 cm-1
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SO2 Not in Standard AIRS-RTA
SO2
Volcanic Ash
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Mt. Etna Eruption Ash and SO2
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Anatahan Eruption Differential Movement of Ash
vs SO2 Cloud
Ash cloud
SO2 cloud
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Dust Detection 1231 and 966 cm-1
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Optical Depth of Dust Longwave Only
MODIS Visible
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Optical Depth of Dust Shortwave Only
MODIS Visible
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SARTA-Scattering used to fit optical depths,
particle size. Results with/without floating
dust altitude (CO2 slicing) and SST
similar Log-normal distri-bution, particle size
spread 1 micron Used ECMWF fields, not
retrievals, for T(z), Q(z), ozone, etc. Only
longwave window channels are used to fit for dust
para-meters
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Sept. 2002
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Oct. 2002
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Nov. 2002
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Dec. 2002
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Jan. 2003
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Feb. 2003
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Mar. 2003
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Apr. 2003
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May 2003
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June 2003
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July 2003
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Aug. 2003
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Expanded Scale Shows Biases of -3K!
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Standard Deviation of Dust Bias
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Cirrus Retrievals SARTA-Scattering RTA
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Mean bias for various cirrus particle habits
O C in K
Wavenumber (cm-1)
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Caption of Previous Figure