Lecture 09. Topical LidarOverview

Introduction to topical lidars

Why topical lidars?

Temperature techniques

Wind techniques

Aerosol techniques

Constituent techniques

Target & altimeter techniques

Summary

Introduction to Topical Lidars

Topics we will discuss in this class are

1. Temperature (structure from ground to thermosphere,diurnal/seasonal/interannual variations, etc.)

2. Wind (structure from ground to upper atmosphere, itsvariations, etc.)

3. Aerosols and clouds (distribution, extinction, composition,size, shape, and variations spatially and temporally)

4. Constituents (O3, CO2, H2O, O2, N2+, He, metal atoms

like Na, Fe, K, Ca, pollution, etc)

5. Target & altimetry (identification, accurate height &range determination, fish, vibration, etc.)

Why Topical Lidars ?

To compare different lidar techniques that addressthe same topic, e.g., how many ways to measuretemperature, and what’s the essential point amongthese different lidars?

To illustrate the strengths and limitations of eachdifferent type of lidars, and give an insight of when andwhere to use what kind of lidars?

To encourage students to explore new phenomena oreffects to invent novel lidars / methods.

Why These Five Topics ? These are five most interesting and hot topics in the

atmospheric/space science, environmental research, andclimate study.

They also have wide applications in environmentalmonitoring, national defense, and industry applications.

The lidar technologies used to address these five topicsrepresent the key technology advancement in the past 20years.

There are also high potentials of future advancement inthese aspects, so encouraging creative students to pursuetechnology innovation, development, implementation, as wellas applying the existing and future technology to conductnovel science/environmental research.

Observables in Atmos Models

AtmosphereTheory & Models

UnderstandAtmosphere EnvironmentPredict

Climate ChangeWeatherForecast

Temperature

Density

AerosolsClouds

WavesSolar Flux

Chemistry

Constituents

Wind

150 200 250 300 3500

20

40

60

80

100

120

MSIS90 Temperature

Temperature (K)

Alt

itude

(km

)

Troposphere

Stratosphere

Mesosphere

Thermosphere

Mesopause

Stratopause

Tropopause

Airglow & Meteoric LayersOH, O, Na, Fe, K, CaPMC

OzonePSC

Temperature Techniques 75-120km: resonance

fluorescence Dopplertechnique (Na, K, Fe) &Boltzmann technique (Fe,OH, O2)

30-90km: Rayleighintegration technique &Rayleigh Doppler technique

Below 30 km: scatteringDoppler technique andRaman technique(Boltzmann and integration)

Boundary layer: DIAL,HSRL, Rotational Raman

AerosolsClouds

Comparison of Temperature Technique

Boundary layer temperatureDifferential Absorption Lidar: Temp-dependence of line strength and lineshape

DIAL

Stratosphere and mesospheretemperature (30-90 km)

Rayleigh Integration Temperature Lidar:atmospheric density ratio to temperature,integration from upper level

Integration Technique:hydrostatic equilibriumand ideal gas law

Troposphere and stratospheretemperature

Rotation Raman Temperature Lidar: ratioof two Raman line intensities andpopulation on different initial energystates

Mesosphere and LowerThermosphere temperature (75-120km)

Resonance fluorescence BoltzmannTemperature Lidar: population ratio onthe lowest two ground states

Boltzmann Technique:temperature dependenceof population ratio

Stratosphere and tropospheretemperature and wind (up to 30km)

High-Spectral-Resolution Lidar: Dopplerbroadening of molecular scattering, ratioof two signals

Lower mesosphere, stratosphereand troposphere temperature andwind (up to 60 km)

Rayleigh Doppler Lidar : Dopplerbroadening of molecular scattering

Mesosphere and LowerThermosphere temperature andwind (75-120 km)

Resonance fluorescence Doppler Lidar:Doppler broadening and Doppler shift ofresonance fluorescence absorption cross-section (scan and ratio techs)

Doppler Technique:temperature dependenceof Doppler broadening

(1 time Doppler shift andDoppler broadening forsingle absorption oremission process)

(2 times Doppler shift andDoppler broadening forRayleigh scattering)

ApplicationsLidarsTechnique

150 200 250 300 3500

20

40

60

80

100

120

MSIS90 Temperature

Temperature (K)

Alt

itude

(km

)

Troposphere

Stratosphere

Mesosphere

Thermosphere

Mesopause

Stratopause

Tropopause

Wind Techniques vs Altitude 75-120km: resonance

fluorescence (Na, K, Fe)Doppler technique (DDL)

FPI: Fabry-PerotInterferometer

Below 60km: RayleighDoppler technique (DDL)

Below 30 km: DirectDetection Doppler technique

In troposphere:Coherent Detection Doppler tech,Direct Detection Doppler tech,Direct motion Detection tech(tracking aerosols, LDV, LTV)

Airglow & Meteoric LayersOH, O, Na, Fe, K, CaPMC

OzonePSC

AerosolsClouds

Comparison of Wind Techniques

Troposphere wind, where aerosolsand clouds are abundant

(Scanning) Aerosol Lidar: tracking aerosolmotion through time

Within the boundary layers, windtunnel, production facility, machineshop, laboratory, etc

Laser Doppler Velocimeter: measuring thefrequency of aerosol scattering across theinterference fringes of two crossed laserbeams

Within the first km range,laboratory, machine shop, etc.

Laser Time-of-Flight Velocimeter:measuring time-of-flight of aerosol acrosstwo focused and parallel laser beams

Troposphere wind, where aerosolsand clouds are abundant

High-Spectral-Resolution Lidar: trackingaerosol / cloud motion through time

Direct Motion DetectionTechnique: derivative ofdisplacement (thedefinition of velocity)(direct application ofvelocity definition or cross-correlation coefficient)

Troposphere wind, especially inboundary layers (up to 15 km),where aerosols are abundant

Coherent Detection Doppler Lidar:Doppler frequency shift of aerosolscattering using heterodyne detection tech

Lower mesosphere, stratosphere andtroposphere wind (up to 50-60 km)

Rayleigh/Mie Doppler Lidar : Dopplerfrequency shift of molecular and aerosolscattering using edge filters and/or fringeimaging

Mesosphere and LowerThermosphere temperature andwind (75-120 km)

Resonance Fluorescence Doppler Lidar:Doppler frequency shift and broadening ofresonance fluorescence absorption cross-section (scan and ratio techniques)

Doppler Wind Technique(Direct Detection orCoherent Detection):wind dependence ofDoppler frequency shift(1 time Doppler shift forsingle absorption oremission process)(2 times Doppler shift forMie and Rayleighscattering)

ApplicationsLidarsTechnique

150 200 250 300 3500

20

40

60

80

100

120

MSIS90 Temperature

Temperature (K)

Alt

itude

(km

)

Troposphere

Stratosphere

Mesosphere

Thermosphere

Mesopause

Stratopause

Tropopause

Aerosol Lidar Technique Comparison

Airglow & Meteoric LayersOH, O, Na, Fe, K, CaPMC

Ozone

AerosolsClouds

Aerosols in mesosphere(Mesospheric Clouds ~ 85 km):Rayleigh/Mie lidar, resonancefluorescence lidar (detuned)

Aerosols in upper stratosphere(Polar Stratospheric Clouds ~ 20km): Rayleigh/Mie lidar,resonance fluorescence lidar

Aerosols in lower stratosphereand troposphere: Rayleigh/Mieelastic-scattering lidar, Ramanscattering lidar, High-Spectral-Resolution Lidar (HSRL)

In all altitude range,polarization & multi-wavelengthdetections help reveal aerosolmicrophysical properties

PSC

HSRL High-Spectral-Resolution-Lidar (HSRL) is to measure the molecule

scattering separately from the aerosol scattering, utilizing the differentspectral distribution of the Rayleigh and Mie scattering.

AerosolScattering

MolecularScattering

150 200 250 300 3500

20

40

60

80

100

120

MSIS90 Temperature

Temperature (K)

Alt

itude

(km

)

Troposphere

Stratosphere

Mesosphere

Thermosphere

Mesopause

Stratopause

Tropopause

Constituent Lidar Techniques

Meteoric Metal LayersNa, Fe, K, Ca, Li, Mg, etc

Ozone

He and N2+ in thermosphere:

resonance fluorescence lidar O in thermosphere: resonance

fluorescence lidar or DIAL fromspace

Metal atoms in 75-120km:resonance fluorescence lidar(broadband or narrowbandtransmitter)

Molecular species in lowerstratosphere & troposphere:Differential absorption lidar(DIAL), Raman scattering lidar,Raman DIAL, RVR Raman DIAL,Multiwavelength DIAL

The key is to use spectroscopicdetection for distinguish species.

H2OO3SO2etc

Comparison of Constituent Lidar Tech

Species,Density

Trace gas absorption inthe extinction terms

Elastic scattering from airmolecules and aerosols

MultiwavelengthDIAL

Species,Density

Trace gas absorption inthe extinction terms

Pure rotational Ramanscattering and Vibrational-Rotational Raman scattering

RVR Raman DIAL

Species,Density

Trace gas absorption inthe extinction terms

Inelastic Raman scatteringfrom N2 or O2

Raman DIAL

Species,Density,Mixing ratio

Trace gas scattering inthe backscatter terms

(no aerosol scattering)

Inelastic Raman scatteringfrom trace gas and referenceN2 or O2

Raman Lidar

Species,Density

Trace gas absorption inthe extinction terms

Elastic-scattering from airmolecules and aerosols

ConventionalDIAL

Density, Temp

Wind, etc

Resonance fluorescence from He, N2+, O in

thermosphereResonanceFluorescence Lidar

Temp, Wind,Density, Wave

Resonance fluorescence from metal atoms in middleand upper atmosphere

ResonanceFluorescence Lidar

InterestsSignal Source & Trace GasTechnique

Range-Resolved spatial & temporal distribution of these species, density, temp, wind and waves

Laser Altimeter (Laser Ranging) The time-of-flight

information from a lidarsystem can be used forlaser altimetry fromairborne or spaceborneplatforms to measure theheights of surfaces withhigh resolution andaccuracy.

The reflected pulsesfrom the solid surface(earth ground, ice sheet,etc) dominant the returnsignals, which allow adetermination of the time-of-flight to much higherresolution than the pulseduration time.

Fluorescence from Liquids and Solids In contrast to free atoms and molecules,

solids and liquids exhibit broad absorption andemission spectra because of the strongintermolecular interactions.

A fixed frequency laser can be used forthe excitation due to the broad absorption.

Following the excitation, there is a veryfast (ps) radiationless relaxation down to thelowest sub-level of the excited state, wherethe molecules remain for a typical excited-state fluorescence lifetime.

The decay then occurs to different sub-levels of the ground state giving rise to adistribution of fluorescence light, whichreflect the lower-state level distribution.

Fixing the excitation wavelength, we canobtain fluorescence spectra. While fixing thedetection channel and varying the excitationwavelength, an excitation spectrum can berecorded.

Summary

Five major topics are chosen for reviewing lidarmeasurement principles and technologies: temperature,wind, aerosol, constituent, and target/altimeter.

For each topic, various technologies will be comparedto reveal the key ideas behind the lidar technologies.

Real lidar data for some of the topics will be givenfor students to perform data inversion, i.e., from rawphoton counts to meaningful physical parameters.

Data inversion principles and procedures will beexplained along the way.

MotivationsFor T/W

Measurement

Model validations

Atmosphericdynamics study

Global climatechange monitoring

Proxy to studygravity waves, tides,planetary waves,etc. dynamicalprocesses

General Circulation versus GlobalThermal Structure

Earth

Summer

Pole

Winter

Pole

cooling

heating

Circulation versus OtherMechanisms

Lidar Temperature atAlbuquerque, NM (35°N)

Lidar Temperature atArecibo, PR (18.35°N)