INTERPRETING SATELLITE OBSERVATIONS OF ATMOSPHERIC COMPOSITION

Spring 2010

Class Objectives:1.Familiarize ourselves with the basic techniques and measurements of composition made from space (Lectures)2.Learn to analyze and critically evaluate satellite data products (Labs)

Pre-requisites:1.Atmospheric Radiation (ATS 622 or equivalent)2.Programming experience (assistance from Colette will be limited to IDL)

Schedule:Lectures (ACRC 212b): Mondays 2-2:50pmLab (ERC 210): Wednesday 2-4pm (lab booked until 5pm)Extra Lab time (ERC 210): Fridays 1-3pm

OBSERVATION PLATFORMS FOR ATMOSPHERIC COMPOSITION

SURFACE IN SITU

SONDES, SURF.-BASED

REMOTE

AIRCRAFT SATELLITES

Horizontal coverage

- - + +

Vertical range - + ~ (up to ~20 km)

~ (interferences)

Vertical resolution

none + + -

Temporal coverage

+ + - ~(polar = daily)

Chemical detail + - + -Cost + + ~ -

STRATOSPHERIC OZONE HAS BEEN MEASURED FROM SPACE SINCE 1979

Method: UV solar backscatter(absorption spectroscopy*)

Scattering by Earth surface and atmosphere

Ozone layer

Last Monday’s ozone layer…Notice the Antarctic ozone hole

*Technique originally applied to ground-based

The satellite era for composition began with Nimbus 7 (launched Oct 1978) which carried LIMS, SAMS, SAMII, SBUV/TOMS (and others)

ATMOSPHERIC COMPOSITION RESEARCH IS NOW MORE DIRECTED TOWARD THE TROPOSPHERE

Tropopause

Stratopause

Stratosphere

Troposphere

Ozonelayer

Mesosphere

…but tropospheric composition measurements from space are difficult:optical interferences from water vapor, clouds, aerosols, surface, ozone layer

Air quality, climate change, ecosystem issues

WHY OBSERVE TROPOSPHERIC COMPOSITION FROM SPACE?

Monitoring and forecastingof air quality: ozone, aerosols

Long-range transport of pollution

Monitoring of sources:pollution and greenhousegases

• solar backscatter• thermal emission• solar occultation• lidar

FOUR OBSERVATIONMETHODS:

Global/continuous measurement capability important for range of issues:

Radiative climate forcing

TROPOSPHERIC COMPOSITION FROM SPACEPlatform multiple ERS-2 ADEOS Terra Envisat Aqua Space

stationSCISAT-1

Aura MetOp-A

Sensor TOMS AVHRR/ SeaWIFS

GOME IMG MOPITT MODIS/MISR

SCIAMACHY

MIPAS *

AIRS SAGE-3 ACE-FTS*

TES OMI MLS* HIRDLS* CALIPSO IASI

Launch 1979 1995 1996 1999 1999 2002 2002 2002 2004 2003 2004 2004 2004 2004 2004 2007

O3 X X X X X X X X X XCO X X X X X X X XCO2 X X X XNO X XNO2 X X X X XHNO3 X X X XCH4 X X X XHCHO X X XCHOCHO X XSO2 X X X XBrO X X XCH3CN XHCOOH XCH3OH XNH3 X Xaerosol X X X X X X X* Only in the UT

THERMAL EMISSION MEASUREMENTS (IR, wave)

EARTH SURFACE

I(To)

Absorbing gas

To

T1

I(T1)LIMB VIEW

NADIRVIEW

Examples: MLS, IMG, MOPITT, MIPAS, TES, HIRDLS, IASI

Pros:• versatility (many species)• small field of view (nadir)• vertical profiling

Cons:• low S/N in lower troposphere• water vapor interferences

SOLAR BACKSCATTER MEASUREMENTS (UV to near-IR)

absorption

wavelength

Scattering by Earth surface and by atmosphere

Examples: TOMS, GOME, SCIAMACHY, MODIS, MISR, OMI, OCO

Pros:• sensitivity to lower troposphere• small field of view (nadir) Cons:

• Daytime only• Column only• Interference from stratosphere

concentration

Retrieved column in scattering atmospheredepends on vertical profile; need chemical transportand radiative transfer models

z

OCCULTATION MEASUREMENTS (UV to near-IR)

EARTH

“satellite sunrise”

Tangent point; retrieve vertical profile of concentrations

Examples: SAGE, POAM, GOMOS

Pros:• large signal/noise• vertical profiling Cons:

• sparse data, limited coverage• upper troposphere only• low horizontal resolution

LIDAR MEASUREMENTS (UV to near-IR)

EARTH SURFACE

backscatter by atmosphere

Laser pulse

Examples: LITE, GLAS, CALIPSO

Intensity of return vs. time lag measures vertical profile

Pros: • High vertical resolution

Cons:• Aerosols only (so far)• Limited coverage

GETTING STARTED WITH IDL & ENS SERVERS

1. Get ENS userid

2. Log on to ENS servers (either from ERC classroom or remotely using ssh & Xming or some other configuration)Servers: linux<1-12>.engr.colostate.edu

lcompute<1-7>.engr.colostate.edu

3. Set up .Xdefaults and .cshrc files in home directory to your preferences (default option: copy those in ~heald/), including PATH information for IDL.

4. source .cshrc to refresh

5. Set up IDL copy over ~heald/IDL into your home directory (GAMAP routines, and idl_startup.pro information)

6. At the prompt anywhere type ‘idl’ to get started!

7. See examples of IDL code in ~heald/ATS681/idl_examples/