instrumental techniques for remote sensing of the...

MOSS, Reunion Island 28 Nov. – 03 Dec. 2016

Instrumental techniques for remote sensing of the atmosphere in the infrared

Mahesh Kumar Sha

Group: Infrared Observation & Lab Experiments

Royal Belgian Institute for Space Aeronomy (BIRA-IASB)

Ringlaan 3, 1180 Brussels, Belgium

Tel. +32-(2)-37 30 389

Email: [email protected]

http://aeronomie.be/en/index.htm

Maido Observatory Summer School (MOSS) Reunion Island 28 Nov. – 03 Dec. 2016

BELGISCH INSTITUUT VOOR RUIMTE-AERONOMIE INSTITUT D’AERONOMIE SPATIALE DE BELGIQUE BELGIAN INSTITUTE OF SPACE AERONOMY BELGISCH INSTITUUT VOOR RUIMTE-AERONOMIE INSTITUT D’AERONOMIE SPATIALE DE BELGIQUE BELGIAN INSTITUTE OF SPACE AERONOMY BELGISCH INSTITUUT VOOR RUIMTE-AERONOMIE INSTITUT D’AERONOMIE SPAT-

Mahesh Kumar Sha, MOSS, Reunion Island 28 Nov. – 03 Dec. 2016 2

Lecture content

1. Scientific background

2. Measurement techniques

3. Basic principles of a Fourier transform spectrometer

4. GHG measurement networks: Description and applications



Scientific context

Global warming a major concern for

survival on Earth

IPCC report: Climate Change 2013



Scientific context

IPCC report: Climate Change 2013



Scientific context

Understanding of the exchange of

Greenhouse Gases (GHGs) and thereby

identifying and quantifying the sources and

sinks of GHGs (e.g. CO2 and CH4) at the

surface

Global estimates of GHG surface fluxes are

presently based on combining ground

based- and satellite measurements

Global Carbon Budget 2016 Fig. source: Basu et. al. ACP 2013 (updated figure)

partitioning

emissions



Scientific context

Global Carbon Project 2016

Perturbation of the global carbon cycle caused by anthropogenic activities,

averaged globally for the decade 2006–2015 (GtCO2/yr)

91% 44%

9% 31%

26%

High growth of atmos. CO2 concentration

in 1987, 1998 and 2015 reflects a strong

El Niño, weakening the land sink

1987 1998 2015



GHG measurement networks

Ground-based in-situ measurement network (surface air sampling, tower ~500 m) Derived fluxes are accurate but are affected by surface exchange and vertical transport

– highly variable but poorly simulated in global models

Limited / no column measurements which limits its use for satellite validation

In-situ aircraft (0 – 20 km) / aircore (0 – 35 km ) measurements Derived fluxes are accurate, measurements are possible at several altitude, but very sparse

Ground-based mid-IR remote sensing measurement network (NDACC-IRWG) Column measurements of GHGs in the mid-IR using FTS instruments, over 20 measurement

sites world wide spanning from the Arctic to the Antarctic locations

Carbon cycle science and validation of satellite instruments

Needs infrastructure, expertise for instrument handling; expensive and not easy to move

instrumentation

Ground-based near-IR remote sensing measurement network (TCCON) Column measurements of GHGs in the near-IR using FTS (Bruker IFS 125HR) instruments, over

22 measurement sites world wide spanning from the Arctic to 45° S

High precision and inter-calibration accuracy, carbon cycle science and satellite validation

Needs infrastructure, expertise for instrument handling, expensive and not easy to move

instrumentation

Ground-based near-IR remote sensing measurement network (COCCON, …) Column measurements of GHGs in the near-IR using portable, low cost FTS

High precision and inter-calibration accuracy, carbon cycle science and satellite validation



Basic principles of an Fourier Transform Spectrometer (FTS)

A FTS performs a physical Fourier transformation of a signal

A monochromatic light source is recorded as a cosine formed intensity

distribution as a function of path length which is then recorded by a detector in

the form of an electric signal

The variation of the path length defines the measured frequency

Schematic diagram of a Michelson interferometer

with linear slide and cube corners

Constructive interference: x = nλ

Destructive interference: x = (n+1/2)λ



Basic principles of an FTS

Spectrum and its corresponding interferogram

FTS

FTS

FT

FT

dxxfF e

xi

2)()(



Solar absorption measurements using FTIR spectrometry

Sun as the source

Sun tracker + FTIR spectrometer

Meteorological sensors

Recorded signal is interferogram (L0)

Interferogram transformed via FFT

into spectrum (L1)

Spectrum is used to retrieve

information of the gases using a

retrieval algorithm (L2)

Meteo station



Ile de La R’eunion – NDACC-IRWG and TCCON site

University of La Réunion at St. Denis (87 m),

Lat: 20.901 °S, Lon: 55.485 °E

NDACC measurements with Bruker IFS 125M –

campaign basis since 2004 and on a continuous

basis since 2009

Bruker IFS 125HR, CaF2 Beamsplitter & optics,

Home-built tracker & electronics

Since September 2011: TCCON (InGaAs and Si) &

NDACC (InSb)

Observatoire du Maïdo (2155 m)

Lat: 21.079 °S, Lon: 55.384 °E

Bruker IFS 125HR, KBr Beamsplitter & optics,

Home-built tracker & electronics

Since March 2013: NDACC (InSb and HgCdTe) &

TCCON (InGaAs)



GHG measurement networks – NDACC-IRWG

Network for the Detection of Atmospheric Composition Change – Infrared

Working Group (NDACC-IRWG): A network of ground-based Fourier Transform

Spectrometers recording direct solar spectra in the mid-infrared.

Recorded absorption spectra are used to retrieve concentrations of a number of

gaseous atmospheric components, including: O3, HNO3, HCl, HF, N2O, CH4, CO,

HCN, C2H6 and ClONO2 as mandatory. Retrieval of other constituents, including

NO, NO2, OCS, C2H2, HCOOH, H2CO, CFCs, HCFCs.

Applications: Derive vertical column amounts of trace gases. Primarily developed

to study the stratospheric distribution of trace gases from high altitude sites away

from urban centers to avoid surface generated pollution. Recently with the

broadening of focus to measure tropospheric gas distribution, sites at lower

latitudes and closer to urban centers are acceptable.



NDACC objectives

Started in 1992 with the following goals

Long-term time series for detecting and understanding changes and trends in

atmospheric composition and parameters

Establish scientific links and feedbacks between climate change and atmospheric

composition

Satellite calibration, validation and gap filling

Collaborative support to scientific field campaigns and other chemistry and

climate observing networks

Model validation



NDACC-IRWG requirements

Spectral range of 700 – 4100 cm-1 (minimum); ~14.3 – 2.4 µm

Maximum OPD >= 250 cm

Continuous spectral coverage (except for the 6-7µm region) in a small number

(< 8) of spectral bands

Make measurements with each filter on a timely interval on an ongoing basis

Routine monitoring of instrument line shape (ILS) using HBr cell spectra

Good alignment necessary with precise information of the modulation efficiency

and phase error

High signal-to-noise ratio of the spectra is necessary to detect weak absorption

lines

Retrieval software available within the network: SFIT and PROFFIT

At Réunion Island measurements performed with Bruker IFS 125M, Bruker IFS

125HR with KBr beamsplitter and liquid nitrogen cooled InSb detector and MCT

detector. The spectrometer is equipped with dual beam acquisition mechanism.



Time series of few species of NDACC-IRWG data at Maïdo

Time series of a

few selected gases



GHG measurement network – TCCON

Total Carbon Column Observing Network (TCCON): A network of ground-based

Fourier Transform Spectrometers recording direct solar spectra in the near-infrared.

Recorded spectra are used to retrieved accurate and precise column-averaged

abundances of atmospheric constituents – CO2, CH4, CO, N2O, H2O, HDO, HF, O2.

Applications: In synergy with other surface measurements, it will improve estimates of

surface fluxes of GHGs => improved prediction of their future concentration =>

better prediction of climate. Data used for carbon flux studies and validation of

satellite measurements.

www.tccon-wiki.caltech.edu



TCCON requirements

Minimum spectral range of 4000 – 9000 cm-1; 2.5 – 1.1 µm

Maximum OPD >= 45 cm, sun tracker with pointing accuracy of 1 mrad (~0.05°)

Surface pressure measurement accuracy better than 0.3 mbar

Surface temperature measurement accuracy better than 1 K

Routine monitoring of instrument line shape (ILS) using HCl cell spectra

Modulation efficiency shall vary by less than 5% over the 0 to 45 cm OPD

Bruker IFS 125HR with CaF2

beamsplitter and room-temperature

DC-enabled InGaAs detectors, and

with DC-enabled Si detectors for the

O2 A – band if the spectrometer is

equipped with dual beam

acquisition.

Source: Bruker IFS125HR_manualBruke



TCCON measurements

Atmospheric measurement

FT

HCl cell measurement

Optical path difference [cm] Wavenumber [cm-1]

Optical path difference [cm] Wavenumber [cm-1]

Zoom of an ifg

Zoom of an ifg FT



TCCON output

Common analysis software GGG uses network wide to do the analysis of the data

Retrieval results are total column amounts of the gases 𝑉𝐶𝑔𝑎𝑠 in molecules cm-2

𝑉𝐶𝑔𝑎𝑠 = 𝑓𝑔𝑎𝑠 𝑧 ∗ 𝑛 𝑧 ∗ 𝑑𝑧∞

𝑍𝑠

, 𝑓𝑔𝑎𝑠 𝑧 = mole fraction of the gas, 𝑛 𝑧 = total

number density, 𝑍𝑠 = surface altitude

𝑉𝐶𝑔𝑎𝑠 tend to be strongly influenced by surface pressure (topography)

Calculate column-averaged dry-air mole fractions (DMFs, 𝑋𝑔𝑎𝑠)

𝑋𝑔𝑎𝑠 = 𝑉𝐶

𝑔𝑎𝑠

𝑉𝐶𝑂2

× 0.2095; where 0.2095 is the DMF of O2

Advantage direct comparison of measurements during different seasons,

between sites and with in-situ measurements, elimination of systematic error

common to gas and O2 cancel out,

Dry-air mole fractions of the gas is then corrected for the air-mass dependence

correction and a bias correction which ties the data to the currently-accepted

WMO scale through calibration factors calculated using in-situ profiles

measurements obtained from aircraft or balloons

Data from each site is available at http://tccon.ornl.gov/



Timeseries of TCCON data at St. Denis station

High accuracy / precision requirement by TCCON

Error in XCO2 < 0.25% (~1 ppm) until SZA ~82°

Error in XCH4 < 0.5% (~5 ppb) until SZA ~85°

Error in XCO < 4% and decreases with SZA

XN2O ~1% (~3 ppm) and reasonably independent of SZA



Timeseries of TCCON data at St. Denis station



TCCON – CO2 and CH4 global data

Wennberg et al. presentation at the annual TCCON meeting, Jeju 2016

St. Denis

TCCON site



TCCON – application towards satellite (OCO-2) validation

Wunch et al. AMTD 2016;

doi:10.5194/amt-2016-227, 2016



TCCON – application towards satellite (OCO-2) validation

Wunch et al. AMTD 2016; doi:10.5194/amt-2016-227, 2016



TCCON – application towards model validation

Copernicus Atmospheric Monitoring Service (CAMS)

Time series of XCO at the Réunion Island TCCON compared to o-suite (red), control run (blue) and high

resolution NRT FC model (yellow) of CAMS

Figure courtesy: Bavo Langerock; Validation report of the CAMS near-real time global atmospheric

composition service – CAMS84_2015SC1_D.84.1.4_201609



TCCON – application towards model validation

CAMS validation of CO2 and CH4 using TCCON data

XCO2

XCH4 Figure courtesy: Bavo Langerock; Validation

report – CAMS84_2015SC1_D.84.1.4_201609



TCCON and NDACC-IRWG FTIR networks summary

Column measurements of GHGs in the near-IR

GHGs – CO2, CH4, CO, N2O, HF, H2O, HDO, O2

Detector – InGaAs and Si Profile scaling retrieval Standardized instruments (Bruker IFS 125HR), measurement setup, data – analysis (GGG) Over 20 measurement sites world wide Investigate the flux of carbon exchange between the atmosphere, land and ocean, satellite validation

Carbon – cycle science and urban GHG emissions Satellite and model validation

Column measurements of trace gases in the mid-IR 20 species among which 10 are mandatory: O3, CO, HCl, HF, CH4, N2O, C2H6, HCN, ClONO2, HNO3 Detector – InSb and HgCdTe Profile retrieval Less uniform instrumentation and setup, data – analysis (SFIT 4, PROFFIT) Over 25 measurement sites world wide Understanding physical and chemical state of the stratosphere and troposphere and assessing the impact of atmospheric changes on climate Ozone chemistry, troposphere chemistry and pollution, VOC's & CFC-substitutes study, ... Satellite and model validation



GHG measurement networks – COCCON

Collaborative Carbon Column Observing Network: COCCON

Karlsruhe Institute of Technology (KIT) started in 2011 the development of a novel

compact NIR-FTIR spectrometer for carbon cycle research. This venture was

tackled in cooperation with Bruker Optik GmbH. The EM27 spectrometer was

decided upon as a starting point.

Measurement container with Bruker IFS 125HR Prototype EM27



GHG measurement networks – COCCON

Results achieved with the prototype were exciting

The spectrometer is now offered as a standard item from Bruker (“EM27/SUN“).

The serial production instrument is an upgrade, e.g. it uses a new acquisition

electronics, offers wider spectral coverage and a redesigned tracker.

M. Gisi, F. Hase, S. Dohe, T. Blumenstock,

A. Simon, A. Keens: “XCO2 measurements with

a tabletop FTS …“ AMT, 2012



Necessity of a new measurement network

Ground-based remote sensing measurements with a portable spectrometer

Column measurements of GHGs in the near-IR using FTS (Bruker EM27/SUN)

RockSolid pendulum interferometer used – stable ILS over longer time

Instruments are light weight, simple handling and portable making it suitable

for mobile network measurement sites world wide, will give significant

contribution towards carbon cycle science and satellite validation

A factor of 5 to 6 times cheaper than the IFS 125HR Bruker spectrometer

High precision and inter-calibration accuracy

Network map of TCCON and NDACC-IRWG stations



COCCON – Instrument overview

EM27/SUN spectrometer from Bruker

RockSolidTM pendulum interferometer

MOPD: 0.9 cm; Resolution: 0.5 cm-1, double sided

InGaAs (Indium Gallium Arsenide) detector used

Spectral range: 5000 – 9000 cm-1

Dimensions: 47 x 63 x 35 cm

Mass: ~ 25 kg including tracker

Sun tracking using optical

feedback by the camtracker

software

Longterm stability of the EM27SUN

XCO2 < 0.1%

Side-by-side intercomparison

Calibration factors before / after

campaign stable within 0.025%

EM27/SUN spectrometers measuring side-by-side

Fig. Source: Bruker



Retrieval strategy – EM27/SUN

PROFFIT (prf-EM27) software used for retrieval of gas profiles

PT profiles with intraday variability used

HITRAN09 database with home made line list for water vapor;

HITRAN08 database used for interfering species

WACCM Ver. 6 climatology used as apriori

Scaling retrieval performed

Retrieval possible even with partial cloudy scenes

Red: IFG dc threashold and modulation fluctuation Black: All data



Spectral windows used by PROFFIT

Examples of

spectral fit

Spectral range used for

retrieval of gases:

O2: 7765.0 – 8005.0 cm-1

H2O: 8353.4 – 8463.1 cm-1

CO2: 6173.0 – 6390.0 cm-1

CH4: 5897.0 – 6145.0 cm-1



EM27/SUN intercalibration

6 spectrometers measured side-by-side at the rooftop of IMK in Karlsruhe

Spectrometer scaling factor

Spectrometer O2 XCO2 XCH4

1 1 1 1

2 0.99965 0.99913 0.99921

3 1.00025 1.00013 0.99958

4 1.0018 0.99997 0.99886

5 1.00312 1.00121 0.9988

6 1.00106 0.99971 0.99907

Source: M. Frey



COCCON – application

Spectra measured by an EM27/SUN – InGaAs detector 5000 – 12000 cm-1



Retrieval results: 28.03.2012

CO2 source from industrial region



Retrieval results: 21.02.2012

CO2 source from industrial region




Few examples of the potential of the portable spectrometers

Upstream-downstream observations of a target area

CO2

CH4




Estimating the CO2 source strength of an area (typically a megacity)

Deployment in Berlin – first of its kind

Participants: T. Blumenstock, M. Frey, J. Groß, F. Hase, M. K. Sha, M. Kiel, G.

Mengistu-Tsidu

Support: R. Kohlhepp (DWD), K. Schäfer (IMK-IFU)




XCO2 time series during the Berlin campaign

F. Hase et al., “Detecting greenhouse gas emissions of Berlin – part 2 ...“, AMT 2015




Simplified source strength of Berlin (Total source strength: 730 kg CO2/sec)





Comparison with simplified model





Mobile platform measurements from a vehicle or ship

(Remote-C group at KIT: A. Butz, F. Klappenbach, J. Kostinek, M.

Berthleff) doi:10.5194/amt-8-5023-2015

Polarstern cruise

(Mar/Apr 2014)




Polarstern cruise (Mar/Apr 2014)

Klappenbach el al., Accurate mobile remote

sensing of XCO2 and XCH4

doi:10.5194/amt-8-5023-2015




Extended ground based network for satellite validation

SCIAMACHY, GOSAT, OCO-2 and future satellite missions

TCCON measurements at KIT + 3 EM27SUN spectrometer measurements

Note: XCO2 gradient along OCO-II track of about 1 ppmv / 10 km analysis TCCON spectra: S. Dohe analysis COCCON spectra: M. Kumar Sha



COCCON – summary

COCCON aim: Increase the density of ground-based XCO2 and XCH4 observations

for the quantification of sources and sinks of atmospheric carbon and for satellite

validation

Dedicated observation of O2, H2O, CO2, CH4 and CO (newly added) in the

spectral range of 4000 and 9000 cm-1

COCCON approach: Create a periphery of EM27/SUN spectrometers around the

TCCON FTIR core. Exploit mobility of the EM27/SUN spectrometers in performing

calibration vs TCCON reference. Temporary arrangement into configurations to meet

certain scientific demands (satellite validation, ground albedo / modelling, encircle

source region)

COCCON start: Initiated by KIT; Instrument recalibration and service to be done in

Karlsruhe (availability of TCCON spectrometer and Bruker support). Operation of

spectrometers in cooperation with local groups. Campaign based measurements

possibilities in collaboration with research groups.

COCCON analysis: Retrieval tools for pre-processing of spectra and subsequent

analysis with PROFFIT. Provide guideline for instrument characterization.

COCCON data: Network wide data archiving facility in collaboration with

NDACC/TCCON. Standardized data format to allow sensible use together with data

from TCCON.



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