remote sensing in ir spectral range •overview • trace gas...

Lecture on atmospheric remote sensing thomas.wagner@iup.uni-heidelberg.de

Remote sensing in 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 1000μm

-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

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)

The observed Intensity is:

= 0if only emission is observed Optical depth

-emission and absorption plays a role

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

-complex radiative transfer modelling has to be applied

( ) ( ) ),,(,,,, TpSTNNTp ijijij νννσνα −⋅⋅=

N: Number density

T: Temperature

p: Pressure

σ: absorption cross section

S: Line width

α: absorption coefficient

gl is the degeneracy and El the energy for state l,μis the overall dipole (or other) moment coupling to the radiation fieldQ(T)= Σgl exp (- El /kT) is the partition functionφij² is the transition matrix element

Scheme of rotational-vibrational transitions

Zu sehen sind die Rotationsschwingungsspektren von HCl (2800 cm-1) und DCl (2200 cm-1) sowie deren erste Obertöne (HCl bei 5600 cm-1 und DCl bei 4400 cm-1) sowie Wasserbanden (3600 cm-1) und CO2-Banden (2600 cm-1).

Example of an absorption FTIR- measurement

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)

Subtraction sequence of an absorption measurement

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

Example of an emission FTIR- measurement

MIPAS-HNO3-observation

Beispiel: N2O-

Isotope

Natural line width:

It can be ignored compared to collision (pressure) broadening at lower altitudes and Doppler (thermal motion) broadening at higher altitudes.

Collision (pressure) broadening:

-collission between molecules shortens lifetimes for specific states-for increasing pressure towards lower altitudes the probability to be scattered increases-the line shape for pressure broadening can be approximated by a Lorentzianline shape:

(Δν: line width for pressure broadening)

The Lorentian line shpae can be retrievd from the *van Vleck and Weisskopf* line shape assuming that the duration of a collision is much shorter than the time between two collisions (impact-approximation)

Lorentian line width:

The Lorentian line width is temperature dependent

Typical value: 2.5 MHz Typical value: 0.75p0: 1hPaT0: 300K

Doppler broadening

-is caused by thermal motion of molecules. The Maxwell distribution depends on temperature and the molecular mass:

According to the Doppler-effect, the line width becomes:

With line width:

By convolution of the Lorentian and Doppler line shape one gets the so called Voigt line shape:

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

Different types of spectrometers:

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

-FTIR, 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

λν =≡

)2cos(1 xAa ⋅⋅⋅= νπ ))(2cos(2 xxAa Δ−⋅⋅⋅= νπ

))2/(2cos()2cos(221 xxxAaaa Δ+⋅⋅⋅Δ⋅⋅⋅=+= νπνπ

[ ])2cos(12)2(cos4 222 xIxAaI in Δ⋅⋅+⋅⋅=Δ⋅⋅⋅⋅== νπνπ

0 1 2 3 4

Phase in W ellenlängen

Wellenzahl:

Überlagerung zweier monochromatischer Wellen mit Phasenverschiebung Δx:

Intensität:

Prinzip des Michelson- Interferometers

Polychromatische InterferenzDa Spektrometer Licht vieler Wellenlängen verarbeiten, entsteht die oben beschriebene Interferenz für jede Wellenlänge. Entsprechend überlagern sich die Interferenz-Intensitäten der einzelnen Wellenlängen zusätzlich.

Fourier Transformation

Atmospheric observations

-ground based measurements

-balloon-borne observations of IR emission

-satellite observations of scattered sun light (NIR)

-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

reolution spectrometer

CO and CH4 column above the Jungfraujoch station

1985 - 1996Mahieu et al., 1997

Total column CO abundance over Zvenigorod (right scale) and corresponding mean tropospheric mixing ratio (left scale). Regression lines for 1970-1984 and for 1985-1997 are shown.

http://www.igac.noaa.gov/newsletter/igac21/trends.html

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

(ISSJ Jungfraujoch)

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

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

Early measurements were carried out witha grating spectrometer; the spectral resolution was limited

A spectrum from 2000 mathematically degraded to the resolution from 1951

Original spectrum from 2000 measured with a FTIR high reolution spectrometer

1951 1988 2000 1951 1988 2000

Total column densities of HCl, measured in Spitsbergen between 1992 and 2000.

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

MIPAS Balloon

MIPAS ClONO2-Messung

SCIAMACHY-Spectral regions

How does the earth look like in the NIR spectral region?

SCIAMACHY on ENVISAT measures backscattered sunlight in the near-IR

Lecture on atmospheric remote sensing thomas.wagner@iup.uni-heidelberg.de1508-1645 nm

Unterer Häufungspunkt der Reflektivität als Maß für wolkenfreie Messungen M. Grezeorski

Lecture on atmospheric remote sensing thomas.wagner@iup.uni-heidelberg.de2265-2380 nm

Unterer Häufungspunkt der Reflektivität als Maß für wolkenfreie Messungen M. Grezeorski

Panel (a) shows the spectrally fully resolved total optical densities for a vertical path for CH4 (V = 3.6 · 1019molec/cm-2) and H2O (V = 6.5 · 1022molec/cm-2) while panel (b) depicts the vertical optical densities of CH4 for different height layers in the atmosphere. The expected total slant optical density (here for A=2.41) is now shown in panel c). Shown is the high resolution optical density and the convolved one that is seen by the instrument, i.e. convolved with I (here: SCIAMACHY slit function in channel 8: Gaussian,FWHM=0.24nm). Starting from this linearisation point, the effect of a change in the vertical column density of CH4 of +1018molec/cm2(i.e. 3% of the total column) in different height layers is shown in panel (d). Panel (e) shows the derivatives (also with respect to CH4perturbations) for different linearisation points, viz. for different water vapour columns (1.3, 6.5 and 32.5 1022molec/cm-2, respectively).The optical densities in (a) and (b) are not convolved.

Typical modelled and measured differential slant optical densities (DSOD) in the CO2 (a)

and CH4 (b) fit windows are shown. In panel (a), CO2 contributes most to the depicted total

DSOD, while there are also very weak absorptions by water vapour. In panel (b),

absorptions by CO2 and H2O marginally add to the strong CH4 signal. In both panels, all

species are fitted simultaneously and make up the total DSOD using a gaussian slit function

with 1.35 nm full width at half maximum.

Example of a CO fit. The upper panel shows the differential slant optical density of all absorbers (CH4, H2O and CO), the middle panelthat of CO. The lower panel shows the residual of the fit.

C. Frankenberg, IUP Heidelberg

CO absorption detected in SCIAMACHY spectra

CO maps correlate well with maps of fire countsC. Frankenberg, IUP Heidelberg

Fire counts measured by MODIS aboard Terra.

C. Frankenberg, IUP HeidelbergCH4 maps from SCIAMACHY

CH4 columns are normalised with respect to CO2 columns

CH4CO2

Aug-Nov 2003

J.F. Meirink, KNMI, Utrecht

Comparison with model results

Aug-Nov 2003

MODIS Enhanced Vegetation Index

The largest differences can be seen in tropical broadleaf evergreen forests

Science, March 2005

In agreement with recent findings of a new CH4source from plants under aerobic conditions

Keppler et al., Nature 2006

Difference SCIAMACHY – Model, Aug-Nov 2003

Different viewing geometries and wavelength ranges:

Direct sun observations provide a high signal to noise ratio

The light path is well defined

High requirements on telescope adjustement

Only special parts of the earth can be monitored

The platform for SAGE II is the Earth Radiation Budget Satellite (ERBS). Nominal orbit parameters for ERBS are:

•Launch Date: October 5, 1984•Planned Duration: 2 years•Actual Duration: ongoing•Orbit: non-sun synchronous, circular at 650 km•Inclination: 57 degrees•Nodal Period: 96.8 minutes

http://www-sage2.larc.nasa.gov/instrument/

Channel Wavelength (nm)

1 1020 2 935 3 600 4 525 5 452 6 448 (nominal) 7 386

SAGE II Channels

Channels Species ApproximateAltitude Range (km)

3-6 O3, NO2 45-60 1, 3-6 O3, NO2, Aerosol (3) 15-45 1, 3-5 O3, Aerosol(3) 10-151, 3 ,4 O3, Aerosol (2) 5-10 1 Aerosol (1) 1-5 Table 2. Algorithm Species and Altitude Range. (3) 1020, 525, and 452-nm extinction profiles; (2) 1020 and 525 nm; (1) 1020 nm only.

http://www-sage2.larc.nasa.gov/data/v6_data/

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

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

CRISTA ist in der Ladebucht desSpace Shuttles eingebaut

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

13.10.202

Model simulation O3 GOME O3 GOME NO2 GOME OClO

(TM3-DAM, KNMI) (IUP Bremen) (IUP Heidelberg) (IUP Heidelberg)

21.09.

22.09.

23.09.

Walburga Wilms-Grabe

Model simulation O3 GOME O3 GOME NO2 GOME OClO

(TM3-DAM, KNMI) (IUP Bremen) (IUP Heidelberg) (IUP Heidelberg)

24.09.

25.09.

26.09.

Walburga Wilms-Grabe

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

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

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

MOPITT instrument

LMC: length modulated gas correlation cell

PMC: pressure modulated gas correlation cell

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

Global CO on 23 March 2000

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

Averaging kernels

Buchwitz et al., 2004

Remedios et al., 2005

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.

Clerbaux et al., 2003

Detection of HNO3 from IMG data.

Surface temperature retrieved from IMG at 976.75 cm−1

(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 se 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

Global distributions of IMG O3 total and partial columns for theApril 1–10, 1997 IMG

period, filtered and averaged over a 5 5 grid and the time period.

Turquety et al., ACP, 2004

Global distributions of IMG CH4 and CO total columns for the April 1–10, 1997 IMGperiod. The data are averaged over the time period and a 55 grid. The corresponding available NDSCmeasurements are represented by colored circles on each map.

From Beer, 2005

TroposphericEmissionSpectrometer (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

Nimbus-1 High Resolution InfraredRadiometer (HRIR) image, taken at nightover western Europe - note the distortion that enlarges Germany and Sweden relative tosouthern countries - the Italians might be aggrieved by the shrinking of the "boot".

Nimbus-1Launch Date August 28, 1964

Operational Period Operational until September 23, 1964

Nimbus-4Launch Date April 8, 1970

Operational Period

Over 10 years until it was deactivated on September 30, 1980

700-mile Long Thermometer. Nimbus-4 took temperature readings of three continents (Africa, Europe andAsia) from 700 statute miles with an infrared camera. The temperature data were reconstructed into aphotograph. White dots on the photo are grid marks which provide scientists with precise latitude andlongitude information. Since the images were measured in heat emitted from Earth, dark areas are land,grey are water and white are clouds.

visible, 0.58-0.68µm

AVHRR 23 Jan 2005 at 1245 UTC

near infra-red, 0.725-1.10µm

short wave infra-red, 1.58-1.64 or3.55-3.93µm

thermal infra-red, 10.3-11.3µm

thermal infra-red, 11.5-12.5µm

Dundee Satellite Receiving Stationhttp://www.sat.dundee.ac.uk/abin/browse/avhrr/2005/1/23/1245

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 for CSUalgorithm, NVAP algorithm, and Susskind's algorithm.

Monochromatic interference

Set up of an interferometer

remote sensing in ir spectral range •overview • trace gas...

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