High-Performance Fourier Transform Infrared Spectrometer:

A Versatile Modular Interdisciplinary Instrument

in the Regional Atmospheric Profiling Center for Discovery

David A. BowdleUniversity of Alabama in Huntsville

NASA/UAH Atmospheric Science "Brown Bag" SeminarDecember 4, 2002

• FTIR Theory

• FTIR Instrument

Optical Layout

Basic Capabilities

• FTIR Science

Planned Use in RAPCD

Potential Interdisciplinary Projects

Brain-storming

OUTLINE AOR

FTIR THEORY AOR

Let spectrum 1 represent a gas sample or a suspended aerosol in the atmosphere or in a laboratory chamber, or an aerosol deposit on

a substrate. Let spectrum 0 represent a blank.

0

1

000

111

0

1

00

11

0

1

0

1

T

T

tG

tG

A

A

L

L

N

N

Photo-counts

SourceRadiance

Receiver Areaand Solid Angle

OpticalEfficiency

Gain, Spectral Resolution,

Intergration TimeTransmission

1,0

0

1

0

1 lnln KT

T

N

NAU

Extinction

UnitsInstrumentArtifacts

01,1

2

1311 OmLkg

mk

m

gCAU nonlinear

ConcentrationIn situ MassExtinctionEfficiency

OpticalDistortion

EffectiveLength

CorrectionReduce

By Design

NICOLET NEXUS 870 FTIR – EXTERNAL VIEW

External Experiment

Data Interface

Left External Beam Port

Dual Detector Compartment Main Sample

Compartment

Dual Source Compartment

Interferometer Compartment

AOR

NICOLET NEXUS 870 FTIR – INTERNAL VIEW

Main SampleCompartment

(KBr Windows)

DTGSDetector

(MIR)

InGaAsDetector

(NIR)

Motorized Path Selection Mirrors

Data & Purge Ports

Power SupplySignal Processor

Michelson Interferometer)

InternalSource

Compartment

AOR

NICOLET NEXUS 870 FTIR – TOP VIEW

Incandescent Source(VIS/NIR)

Globar Source(MIR)

CondensingMirror

(Source)

MotorizedAperture

Wheel

CondensingMirror

(Sample)

MotorizedCollimating

Mirror

Michelson Interferometer)

HeNe Laser

AOR

LeftExternal

Beam

ExternalSourceBeam

NICOLET NEXUS 870 FTIR – OPTICAL PATH

LeftExternal

Beam

AOR

NICOLET NEXUS 870 FTIR – INTERFEROMETER

HeNe Laser

Moving Mirror Drive

Piezo-Electric Dynamic Alignment

FixedMirror

LaserPickoffMirror

Dynamic Alignment Phase Detectors

KBr Beam Splitter

Extended Range

AOR

NICOLET FTIR CAPABILITIES AOR

Linear scan Scan speeds up to ~50 Hz

Spectral resolution as fine as ~0.125 cm-1

Spectral range from 375-11,000 cm-1

Automated experiment setup including alignment; recognition of key components and accessories; selection of source, detector, and sample chamber; diagnostics; etc.

Easily adaptable to custom attachments

Step scan Amplitude modulation

• Chopper, with lock-in-amplifier• Repeatable sample phenomena

• Slow (ms) to ultra-fast (s) processes Phase modulation

• Dithering of fixed mirror•Analysis of thin layers

FTIR OPERATION AOR

Attend demonstration

of Nicolet Nexus 870 FTIR

in NSSTC Room 2014

after presentation and

brainstorming session

NICOLET NEXUS FTIR - REMOTE SENSING STATION

AOR

Solar TrackerChimney

Horizon ScannerChimney

OpticalCurtainsOptical

Bench

CoolingWater

& Drain

Utility Buss Bar110, 208 1/Ph, 2083/PhAir, Vacuum, Nitrogen

Data Ports, Light Switch

DimmingIncandescents

Not Shown:Dimming Fluorescents

Casework

HEPAFilters

AEROSOL ICROPHYSICS AND RADIOMETRY LAB

AOR

AEROSOL ICROPHYSICS AND RADIOMETRY LAB

AOR

RAPCD CHIMNEY INSPECTION

Mike Newchurchgoes to great lengths

to make sure RAPCD works

Jay Lekointerviews for

a RAPCD research position

AOR

PLANNED USE IN RAPCD

Composition and Concentration of Particles and Trace Gases

Atmospheric Chemistry Measurements

Column optical depth, using multi-spectral Langley plots from a roof-mounted solar tracker with dithered pointing

Horizontal optical thickness, using one-way or two-way transmission with a roof-mounted alt-azimuth scanner

Cloud initiation, cloud particle phase, fog chemistry

Aspirated sample analysis, using bottles, filters, impactors

Size-dependent composition of airborne mineral dust

Deployment in RAPCD mobile van

AOR

PLANNED USE IN RAPCD

Composition and Concentration of Particles and Trace Gases

Atmospheric Chemistry Simulations

Artificial aerosols suspended in air, deposited on substrates

Heterogeneous chemical reactions, chemical kinetics

Calibration/Validation of Atmospheric Sensors and Models

Backscatter enhancement spectra from particle coatings

Composition of calibration particles for lidar backscatter

Optical distortion in particulate deposits on substrates

Scattering from non-spherical particles (e.g., pollen grains)

Polarimetry in transmission, forward scatter, backscatter

AOR

INTERDISCIPLINARY PROJECTS

Satellite remote sensing validation

Precipitation chemistry (remote or aspirated)

Spectral backscatter from simulated river surfaces

Optical emissions and chemical byproducts of lightning

Spectroscopy of simulated interstellar dust grains

Solar spectroscopy and solar variability

Nano-technology, bioaerosol detection

Brief brain-storming session after seminar dismisses

AOR

SUMMARY AND CONCLUSIONS

New high-performance FTIR obtained for RAPCD

Provides versatile tool for atmospheric chemistry research, in both ambient and simulated environments

Initial installation in RAPCD aerosol lab expected in January. Rooftop scanners to be acquired in future proposals.

Offers opportunity for interdisciplinary research ventures by adding modular commercial or in-house accessories

AOR