Chip TrepteNASA Langley Research Center

The A-Train: Exploiting the Electromagnetic Spectrum

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

A-Train Members

Mission Instruments Purpose

Aqua (2002) 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

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)

Basic Properties of LightElectromagnetic 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)

Electromagnetic Spectrum

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

Emission of LightObjects 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)

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

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 existsMesosphere and above – blueish hues

Atmosphere CompositionGas Percent Volume

Nitrogen 78.084%

Oxygen 20.946%

Argon 0.9340%

Carbon dioxide

0.039455%

Neon 0.001919%

Helium 0.000524%

Methane 0.000179%

Krypton 0.000114%

Hydrogen 0.000055%

Nitrous oxide 0.00003%

Carbon monoxide

0.00001%

Xenon 0.000009%

Ozone 0.000007%

Water Vapor ~0.4% (1-4% at surface)

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

Techniques for Remote Sensing

Emission

Light source

Transmission

DetectorDetector

Detector

atmosphere

Scattering from incoherent

source

DetectorSource

Scattering from coherent source (Active Remote

Sensing)

OMI - SO2, ash, BrO

TES - SO2

MLS - UTLS SO2, HCl, IWC

MODIS - SO2, ash, sulfate, ice

AIRS - SO2, ash, sulfate, ice, SO2 profile

CALIOP - aerosol altitude, phase/type

Exploiting A-Train synergy for volcanic cloud studies

The A-Train

Aura Aqua

CALIPSO

CloudSat

CPR – precipitation, hydrometeors

Soufrière Hills volcano (Montserrat) eruption, May 2006

[Carn et al., 2007; Prata et al., 2007]

~0.2 Tg SO2

Soufrière Hills volcano (Montserrat) eruption, May 2006

[Carn et al., 2007; Prata et al., 2007]

~0.2 Tg SO2

Soufrière Hills volcano (Montserrat) eruption, May 2006

[Carn et al., 2007; Prata et al., 2007]

~0.2 Tg SO2

Soufrière Hills volcano (Montserrat) eruption, May 2006

[Carn et al., 2007; Prata et al., 2007]

~0.2 Tg SO2

CALIPSO first light – 7 June 2006

CALIPSO ‘first light’ - 7 June 2006

OMI SO2 - 7 June 2006OMI SO2 – 7 June 2006

Aqua-MODIS RGBOctober 4 2010

Clear air in Beijing

MODIS-RGB October 8 2010

Hazardous air in Beijing

MODIS-RGB + Aura- OMI SO2 October 8 2010

SO2 pollution from coal burning Power Plants and industries (metal smelting)

MODIS 12 µm (Channel 32)

Combined CALIPSO/CloudSat Cloud Observations“Great Arc Cloud”

CALIPSO 532 nm Backscatter

CloudSat Cloud Mask

CALIPSO 1064 nm Backscatter

CloudSat Radar Reflectivity (dBZ)

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Aerosol and Cloud Observations over Southern AsiaMODIS only

October 25, 2006

Aerosol and Cloud Observations over Southern AsiaCALIPSO and MODIS

October 25, 2006