1. The A-Train: Exploiting the Electromagnetic Spectrum
Chip Trepte
NASA Langley Research Center

2. What is the A-Train?
Constellation of satellites flying in formation to observe the same area and almost the same time but with using different techniques
Orbit crosses equator around 1:30 pm local time or in the ‘Afternoon’ and (originally) lead by the Aqua mission
Named after the ‘Take the A-Train’ jazz tune composed by Billy Stayhorn and made popular by Duke Ellington’s band.
Data collected synchronously gives more- complete answers to important scientific questions than would be possible with observations collected at different times

3. A-Train Members Mission Instruments Purpose Aqua (2002) CALIPSO (2006)
AIRS, AMSR-E, AMSU-A, CERES, HSB, MODIS
Clouds, temperature, moisture, precipitation, ice, snow, reflected radiation and Earth emitted radiation, sea surface temperature
CALIPSO (2006)
CALIOP, IIR, WFC
Profiles of aerosols and clouds, IR properties of clouds
CloudSat (2006)
CPR
Profiles of cloud water amount
Aura (2004)
HIRDLS, MLS, OMI, TES
Composition and temperature of upper atmosphere
GCOM-W (2012)
AMSR2
Precipitation, relative humidity, temperature

4. A-Train Instrument Techniques
Mission
Instruments
Aqua (2002)
AIRS (IR sensor)
AMSR-E, AMSU-A (microwave sensor)
CERES (visible/IR sensor)
HSB (microwave sensor)
MODIS (visible/IR sensor)
CALIPSO (2006)
CALIOP (active lidar)
IIR (IR sensor)
WFC (visible sensor)
CloudSat (2006)
CPR ( active radar)
Aura (2004)
HIRDLS (IR sensor)
MLS (microwave sensor)
OMI (visible sensor)
TES (IR sensor)
GCOM-W (2012)
AMSR2 (microwave sensor)

5. Basic Properties of Light
Electromagnetic radiation propagates as a wave
oscillating electric and magnetic fields
theory provided by James Clerk Maxwell (1865)
Three primary characteristics
intensity (amplitude of wave)
color (wavelength or frequency of wave)
polarity (propagation plane of wave)

6. Electromagnetic Spectrum

7. Attenuation of Light
Transmission of light through a substance is affected by the absorption and scattering of light.
August Beer (1854), Johann Lambert (1760) discovered this relationship

8. Emission of Light
Objects of different temperatures emit light that peak at different wavelengths
Hotter objects emits most radiation at shorter wavelengths
Cooler objects emit most radiation at longer wavelengths
Discovered by Wilhelm Wien (1893)

10. Possible interactions between photons and molecules/atoms
Visible and UV light: changes electron distribution in orbits (orbit transitions)
Infrared light: changes vibration/rotation states
Microwave light: changes rotation states

11. Earth’s Atmosphere Limb View of Atmosphere:
Troposphere – orange/yellow shades and contains > 80% of mass and holds almost all water and clouds
Stratosphere – pinkish hue and where ozone layer exists
Mesosphere and above – blueish hues

12. Atmosphere Composition
Gas
Percent Volume
Nitrogen
78.084%
Oxygen
20.946%
Argon
0.9340%
Carbon dioxide %
Neon %
Helium %
Methane %
Krypton %
Hydrogen %
Nitrous oxide %
Carbon monoxide %
Xenon %
Ozone %
Water Vapor
~0.4% (1-4% at surface)

13. Atmospheric Aerosols/Particles
Particles or Aerosols are present throughout the atmosphere
pollen, dust, smoke ash, rain or sulphuric acid droplets
ice and snow crystals ……
Composed of many substances
water, ice, water/ice,
soluble gases, carbon cores …
Scatter light in many ways
geometric optics (rainbows, halos
Rayleigh (molecular) scattering
Mie scattering
Range in size 6 or 8 orders of magnitude (.01 microns to 10 cm)
Gustav Mie
Lord Rayleigh

14. Techniques for Remote Sensing
Detector
Detector
Light source
Emission
atmosphere
Transmission
Detector
Source
Detector
Scattering from incoherent source
Scattering from coherent source (Active Remote Sensing)

15. CALIOP - aerosol altitude, phase/type
Exploiting A-Train synergy for volcanic cloud studies
Aura
Aqua
OMI - SO2, ash, BrO
TES - SO2
MLS - UTLS SO2, HCl, IWC
MODIS - SO2, ash, sulfate, ice
AIRS - SO2, ash, sulfate, ice, SO2 profile
CloudSat
CALIPSO
CPR – precipitation, hydrometeors
CALIOP - aerosol altitude, phase/type
The A-Train

16. Soufrière Hills volcano (Montserrat) eruption, May 2006
~0.2 Tg SO2
[Carn et al., 2007; Prata et al., 2007]

17. Soufrière Hills volcano (Montserrat) eruption, May 2006
~0.2 Tg SO2
[Carn et al., 2007; Prata et al., 2007]

18. Soufrière Hills volcano (Montserrat) eruption, May 2006
~0.2 Tg SO2
[Carn et al., 2007; Prata et al., 2007]

19. Soufrière Hills volcano (Montserrat) eruption, May 2006
~0.2 Tg SO2
[Carn et al., 2007; Prata et al., 2007]

20. CALIPSO first light – 7 June 2006
OMI SO2 – 7 June 2006
OMI SO2 - 7 June 2006
CALIPSO ‘first light’ - 7 June 2006

21. Clear air in Beijing
Aqua-MODIS RGB
October

22. Hazardous air in Beijing
MODIS-RGB
October

23. MODIS-RGB + Aura- OMI SO2 October 8 2010
SO2 pollution from coal burning Power Plants and industries (metal smelting)

24. Combined CALIPSO/CloudSat Cloud Observations
“Great Arc Cloud”
MODIS 12 µm (Channel 32)

25. CALIPSO 532 nm Backscatter
Height 15 10 5
CALIPSO 532 nm Backscatter
Height 15 10 5
CALIPSO 1064 nm Backscatter
Height 15 10 5
CloudSat Cloud Mask
Height 15 10 5
CloudSat Radar Reflectivity (dBZ)

26. Aerosol and Cloud Observations over Southern Asia
MODIS only
October 25, 2006

27. Aerosol and Cloud Observations over Southern Asia
CALIPSO and MODIS
October 25, 2006