Remote sensing in the IR spectral range •Overview • Trace...

Lecture on atmospheric remote sensing thomas.wagner@mpic.de

Remote sensing in the IR spectral range

• Overview

• Trace gas spectra

• Spectrometer concepts

• Trace gas measurements from different platforms

• Imaging satellite instruments

moleculesaerosols

Cloud droplets

rain droplets

Remote sensing in IR spectral range

Wavelengths from ~1 to 1000m

-vibrational + rotational transitions

In the IR spectral range, typically emission spectra are analysed

In some cases also absorption spectra of the solar radiation are measured

NearIR

ThermalIR

Usually IR spectra are given as function of wavenumberWavenumber = 1 / Wavenumber is usually given in 1 / cm

3.3 m5 m10 m20 m

Infrared emission spectrum of the Earth atmosphere in the mid-infrared region (700–2250 cm−1) calculated with the radiative transfer model LBLRTM for mid-latitude conditions (summer, unpolluted scenario). The most important absorption bands of different trace gases (O3, CO, CO2, H2O, CH4, N2O) are indicated.

(Orphal et al., 2005)

~4.4m~15.3m

The observed Intensity is:

= 0if only emission is observed Optical depth

-emission and absorption have to be considered

-typically no simple inversion (like in the UV/vis) is possible

-complex radiative transfer modelling has to be applied

dsdWithout the surface term and with :

For small optical depth the observed signal becomes proportional to the optical depth

),,(,,,, TpSTNNTp ijijij

N: Number densityT: Temperaturep: Pressure: absorption cross sectionS: Line width

: absorption coefficient

Optical depth

From the measured optical depth, the absorption coefficient, or finally the number density of a trace gas can be derived.

Als Auswahlregeln bei der RotationsAls Auswahlregeln bei der Rotations--Schwingungsspektroskopie erhält man:Schwingungsspektroskopie erhält man:

1v 1J ,0

01Rotations-Schwingungsterme: S(v, J) v BJ J 12

Rotations-Schwingungspektroskopie

linear in quadratisch in J

Vibrationsquantenzahl Rotationsquantenzahl J

Termschema:Termschema:

Eine Linie Eine Linie steht für einen steht für einen kombinierten kombinierten RotationsRotations--SchwingungsSchwingungs--übergang!übergang!

Man erhält ein Spektrum der folgenden Art:Man erhält ein Spektrum der folgenden Art:

The rotational-vibrational spectra are determined by the molecules symmetry and complexity

Methyl ethyl ketone (13 atoms, nonsymmetric)

Benzene(12 atoms, symmetric)

Formaldehyde(4 atoms, non-linear)

Acetylene(4 atoms, linear)

Nitric oxide(heteronuclear, diatomic)

Example of an absorption FTIR- measurement

Subtraction sequence of an absorption measurement

Lecture on atmospheric remote sensing thomas.wagner@mpic.dehttp://www-imk.fzk.de:8080/imk2/mipas-b/bestfit.gif

Example of an emission FTIR- measurement

MIPAS-HNO3-observation

Example: N2O-Isotopes

www2.nict.go.jp/kk/e414/shuppan/ kihou-journal/journal-vol49no2/4-06.pdf

From pressure broadening information on vertical profiles can be obtained

(but often (only) total columns are determined)

Information content and the sensitivity of a remote sensing measurement can be described by so called averaging kernels. They are determined during the retrieval process:

The measured spectra are simulated using a) assumed atmospheric profilesb) a radiative transfer modelc) an instrument simulation modelThe atmospheric profile is varied until measured and simulated spectra agree.

For the comparison with other data sets (e.g. model results) theaveraging kernels have to be applied:

')',,(',,,),,(0

dzzyxModelzzyxAKzyxtMeasuremenTOA

ztmeasuremen

e.g. concentrationor total or partialcolumn density

e.g. concentrationor partial column density

Can be extended to 3 dimensions

Averaging kernels: indicate height-dependent sensitivity

Lecture on atmospheric remote sensing thomas.wagner@mpic.dehttp://www.ifac.cnr.it/retrieval/documents/AK_report.pdf

HNO3 from MIPAS

Thermal IR

Averaging kernel for limb observations

Narrow kernels are ‚good‘

Comparison to ozone sonde

Segers et al., ACP 2005

O3 from SCIAMACHY

Different types of spectrometers:

-Grating spectrometer: simple setup, medium spectral resolution, typical for early measurements, today: satellite instrument CRISTA

-Fourier Transform IR, e.g. MIPAS: complex system with moving parts, high spectral resolution (typical instruments today)

-Etalon spectrometers (e.g. CLAES): high spectral resolution in selected wavelength windows

-gas correlation filter radiometer (e.g. satellite instrument MOPITT)

Michelson-Interferometer

Monochromatic interference

Set up of an interferometer

Fourier Transformation

Atmospheric observations

-ground based measurements

-air-borne observations of IR emission

-satellite observations of direct sun light

-satellite observations of IR emission (limb)

-satellite observations of IR emission (nadir)

-satellite observations imagers (IR emission nadir)

Schematic illustration of theinstrumental setup used. Thesolar/lunar tracker follows the course of the sun/moon and feeds a parallel light beam into the spectrometer. In the interferometer the light beam is splitted into the two rays by the beamsplitter.Several detectors are mounted which allow to record the whole spectral region from the IR at 700/cm (14 µm) up to the UV at 33000/cm (300 nm).

Increase of free tropospheric CO from 1951 to 1985(ISSJ Jungfraujoch)

Early measurements were carried out with a grating spectrometer; the

spectral resolution was limited

A spectrum from 1985 mathematically degraded to the

resolution from 1951

Original spectrum from 1985 measured with a FTIR high

resolution spectrometer

CO and CH4 column above the Jungfraujoch station

1985 - 1996Mahieu et al., 1997

Seasonal cycle of freetropospheric CO from 1950/51 and 1985-87

(ISSJ Jungfraujoch)

www.ifjungo.ch/reports/1999_2000/pdf/09.pdf

Original spectrum from 2000 measured with a FTIR high resolution spectrometer

Increase of several species from 1951 to 2000 (ISSJ Jungfraujoch)

Early measurements were carried outwith a grating spectrometer; the spectral resolution was limited

A spectrum from 2000 mathematically degraded to the resolution from 1951

H2OH2O H2O

CO2 CO2

arrows: CFC-12 (CCl2F2)

Griesfeller, A.: Validierung von ENVISAT-Daten mit Hilfe von bodengebundenen FTIR-Messungen, Dissertation, FZK Report No. 7072, Forschungszentrum Karlsruhe, Germany, 2004.

During polar night NOx is converted into HNO3

MIPAS Balloon

MIPAS ClONO2-Messung

MIPAS Balloon

K. Weigel et al., CRISTA-NF measurements during AMMA, AMT 2010

Measurements contaminated by clouds

Lecture on atmospheric remote sensing thomas.wagner@mpic.deK. Weigel et al., CRISTA-NF measurements during AMMA, AMT 2010

ATMOS instrument on the space shuttle

Atmospheric Trace Molecule Spectroscopy (ATMOS)

Four Missions:

-Spacelab: 1985-ATLAS-1: 1992-ATLAS-2: 1993-ATLAS-3: 1994

Key profiles from ATMOS Spacelab 3 sunset occultation data.

The ACE satellite: IR sun occultation measurementshttp://www.ace.uwaterloo.ca/images/ACE_occultation.jpg

http://www.ace.uwaterloo.ca/images/ACE_occultation.jpg

Bernath, Peter (2006), Atmospheric Chemistry Experiment (ACE): Analytical Chemistry from Orbit, Trends in Analytical Chemistry, Vol. 25, No. 7., pp. 647-654

Carleer, M.R., et al. (2008), Validation of water vapour profiles from the Atmospheric Chemistry Experiment (ACE), Atmos. Chem. Phys.Discuss., 8, 4499-4559, 2008 (PDF)

From ACE, also high resolution solar spectra were generated

Limb-Beobachtung

THE (Cryogenic Limb Array Etalon Spectrometer ) CLAES INSTRUMENTCLAES infers the amounts of gases in the stratosphere from the measurement of the unique infrared emission features by combining a telescope with an infrared spectrometer and solid state detectors, and cryogenically cooling the whole instrument below 150 Kelvin to minimise its own thermal infrared emissions. The spectrometer operates over the wavelength range 3.5 to 12.9 microns.Spectroscopy is performed by tilt scanning one of the four solid etalons between one or more of the nine blocking filters. The nine filters are centered at 2843, 1897, 1605, 1257, 925, 879, 843, 792 and 780 cm-1.

http://www.lmsal.com/9120/CLAES/mission.html

24 hours of ClONO2 (top) and HNO3 (bottom)data at 21 km as measured by CLAES in theArctic stratosphere for individual days between July 1992 and May 1993. (Roche et al., J. Atmos. Sci., 51, 2877-2902, Oct. 15, 1994.] )

http://www.crista.uni-wuppertal.de/images/space.png

CRISTA ist in der Ladebucht desSpace Shuttles eingebaut

CRISTA-SPAS has successfully completed two missions:

CRISTA 1 was launched on November 3, 1994 with STS-66 Atlantis.On November 12 the satellite was retrieved and two days later returned to Earth. The STS-66 payload alsoincluded the SSBUV experiment and the ATLAS-3instrument package.

CRISTA 2 was launched on August 7, 1997 with STS-85 Discovery.The Space Shuttle landed on August 19, 11:08 UT at NASA Kennedy Space Center, Florida.

Measured CRISTA spectra of a single altitude scan in the tropical upper troposphere. Shaded spectral signatures originate from H2O emissions of weak lines.

Fig. 1 Viewing geometry of CRISTA

N20-Karte am 06. November 1994 in 30 km Höhe

Assimilated water vapor field at 215 hPa on August 12, 1997.

MIPAS/ENVISAT

MIPAS on Envisat

http://www-imk.fzk.de/asf/ame/ClosedProjects/assfts/P_III_12_Glatthor_N.pdf

13.5km

16.4km

19.4km

40.3km

ClO emission

17.9.2002

20.9.2002

13.10.2002

www.copernicus.org/EGU/acp/acpd/4/6283/acpd-4-6283.pdf

16.01.2003

OClO from GOME-1

-satellite observations of IR emission/absorption (nadir)

IR / MW: ideal case 1: surface is warmer than atmosphere:

=> only absorption has to be considered

IR / MW: ideal case 2: surface is colder than atmosphere:

=> only emission has to be considered

IR / MW: typical case: Tsurface and Tatmosphere are similar:

emission and absorption have to be considered

Clouds and aerosols further complicate the measurement

Radiative transfer simulations are needed

Typically the thermal contrast between the surface and the air directly above is small

High Resolution Infrared Radiation Sounder Version 2 (HIRS/2) on he TIROS Operational Vertical Sounder (TOVS)

Sensitivity of TOVS H2O observation for different IR wavelengths

Soden and Bretherton, 1996

Engelen and Graeme, 2002

Retrieved water vapor between 1000 - 700 mb, 700 - 500 mb, and 500 - 300 mb from TOVS

http://www.atmosp.physics.utoronto.ca/MOPITT/MATR.pdf

MOPITT measures emitted (4.6 m) and and reflected (2.3 m) radiation

MOPITT instrument: Gas correlation technique

Transmission is varied

Gas cell Broad band radiometer

Signal =

emission

transmission

atmospheric emission

MOPITT instrument: Gas correlation technique

atmospheric emission: 0 atmospheric emission: x

Instrument transmission: 0

Instrument transmission: 0.5

Difference signal: 0

Difference signal: 0.5x

MOPITT instrument

LMC: length modulated gas correlation cell

PMC: pressure modulated gas correlation cell

Transmission convolved with the detector sensitivity (4.6 m) for different CO absorptions

Global CO distribution from SCIAMACHY (bottom) and MOPITT (top)

Averaging kernels

Remedios et al., 2005

Buchwitz et al., 2004

20.09.2004

Lecture on atmospheric remote sensing thomas.wagner@mpic.dehttp://suzaku.eorc.jaxa.jp/GLI2/adeos/Project/Img.html

IMG Main Characteristics

Spectral Range ofMeasurement

714-303 cm (14 -3.3um)

Wave number resolution 0.1cm (apodized) Absolute accuracy ofmeasurement < = 1k

Stability of measurement <= 0.1k

Interferogram scan time <= 10sec Sampling perintergerogram <= 100,000

Mass < 115kg

Power consumption < 150w

Approximate Size within1000x800x500mm

Interferometric Monitor for Greenhouse Gases (IMG)(1996 – 1997)

IMG spectrum (in transmittance units) in the 600–2500 cm−1 spectral range recorded over South Pacific (−75.24, −28.82) on 4 April 1997, 04:00:42GMT (top). Radiative transfer simulations for absorption contributions due to strong (middle) and weak (bottom) absorbers are also provided.

Zoom next slide

Clerbaux et al., 2003

IMG:InterferometricMonitor for GreenhouseGases

Detection of HNO3 from IMG data.

(a) Best ozone spectral fits for IMG observations above the Uccle (left plot) and Ny-Alesund (rightplot) sites. The selected scenes correspond to surface temperatures of 280 and 255 K, respectively. The dashed lines at ±107 W/(cm2 sr cm1) correspond to the value selected to constrain the retrievals.

(b) Retrieved ozone profiles in number density units and relative differences calculated with respect to the smoothed ozone sonde profiles at the two locations. The a priori profile is also shown.

Coheur et al., JGR 2005

IMGUccle Ny Alesund

Global distributions of IMG CH4 and CO total columns for the April 1–10, 1997 IMG period. The data are averaged over the time periodand a 5° x 5° grid. The corresponding available NDSCmeasurements are represented by colored circles on each map.

Atmospheric IR Sounder

http://airs.jpl.nasa.gov

AIRS measures upwelling radiances in 2378 spectral channels in the infrared (IR) from 3.74 µm to 15.4 µm.

650 – 2700 cm^-1 wavenumbers, spectral resolution: 0.5 – 2cm-1

AIRS is a grating spectrometer

Atmospheric Infrared Sounder (AIRS) originally designed to measure atmospheric water vapor and temperature for weather forecasting Also atmospheric CO and CO2 can be retrieved for the mid-troposphere(about 8 km above the surface)

TES observes atmospheric emissions in both limb and nadir geometry

http://tes.jpl.nasa.gov/

TES is a high-resolution,infrared, imaging Fourier-transform spectrometer with spectral coverage of 650 to 2250 cm-1 at a spectral resolution of 0.1 cm-1 (low resolution) or 0.025 cm--1

(high resolution)

From Beer, 2005

Tropospheric EmissionSpectrometer (TES)

First TES global map oftropospheric O3 (9/21/2004)

GEOS-CHEM modelfor 9/21/2004

CO Column from TES, 9-20-04

CO Column from MOPITT, 9-20-04

Zhang et al., 2006

Launched in 2006 on METOP-A.

A second and third instrument will be mounted on the METOP-B and C satellites with launches scheduled in August 2012 andOctober-November 2016.

Infrared Atmospheric Sounding Interferometer (IASI)

Infrared Atmospheric Sounding Interferometer

Clarisse et al., ACP 2008

Spectrum outside volcanic plume

Spectrum inside volcanic plume

Ratio spectrum

Detection of SO2 in volcanic plumes

Clerbaux et al., ACP 2008

Detection of several trace gases in biomass burning plumes

Fires in east Siberia, May 2007

(Tropospheric) Ozone from IASI

Nimbus-1Launch Date August 28, 1964

Operational Period Operational until September 23, 1964

Nimbus-1 High Resolution Infrared Radiometer (HRIR) image, taken at night over western Europe - note the distortion that enlarges Germany and Sweden relative to southern countries.

0.58-0.68µm 1.58 - 1.64µm 10.3 - 11.3µm

AVHRR, chan. 1

29 Apr 2006 at 1330 UTC

Dundee Satellite Receiving Station (http://www.sat.dundee.ac.uk)

AVHRR, chan. 3 AVHRR, chan. 4

Measurements of radiometers: Clouds are bright

Thermal IRVisible Near IR

Short summary for IR atmospheric remote sensing:

-in the thermal infrared a large number of molecules can be measured

-instruments at different platforms and with different viewing geometries

-pressure broadening allows to retrieve height information (for stratosphere)

-instrumentation is often very complex (deep temperatures, interferrometers)

-from satellite, usually the sensitivity for trace gases in the boundary layer is low

Remote sensing in the IR spectral range •Overview • Trace...

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