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Department of Mechanical Engineering 2012-2013 Students: Seth Davies, Betsy Farris, Alex Mende, Constantino Tadiello, Joseph Williams Advisors: Jordan Rath and Dr. Azer Yalin. Research Motivation.

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Department of Mechanical Engineering

2012-2013

Students: Seth Davies, Betsy Farris, Alex Mende, Constantino Tadiello, Joseph Williams

Advisors: Jordan Rathand Dr. AzerYalin


Research motivation
Research Motivation

The laser sensor project is in support of the NASA ASCENDS Program (Active Sensing of CO2Emissions over Nights, Days, and Seasons) whose main goal is to develop a better understanding of the global spatial distributions of atmospheric carbon dioxide (CO2). To do so, the ASCENDS program employs laser sensors from aircrafts to the ground.

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Problem statement
Problem Statement

  • Validate the feasibility of using Cavity Ring-Down Spectroscopy to measure absorption spectra at different temperatures and pressures representative of different altitudes within the troposphere.

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Objectives
Objectives

  • Simulate a temperature range from -20°C to 20°C

  • Simulate a pressure range from 0.1 bar to 1 bar

  • Record spectral data at T, P corresponding to NASA’s CO2 distribution

  • Compare recorded spectra to simulated spectra (HITRAN)

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Constraints
Constraints

  • 90 centimeter sampling cell length

  • No foreign particulates on the CRDS mirrors

  • DAQ system with limited simultaneous sampling

  • Budget of $3000

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Distribution of tropospheric co 2 nasa s region of interest
Distribution of Tropospheric CO2NASA’s Region of Interest

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Introduction to cavity ring down spectroscopy crds
Introduction to Cavity Ring-Down Spectroscopy (CRDS)

More CO2 → Faster Decay → Smaller τ

Less CO2 → Slower Decay → Larger τ

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Geometric Modeling/Design Summary

Cutaway View of System

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Geometric Modeling/Design Summary

Fully Enclosed System

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Temperature and pressure measurement
Temperature and Pressure Measurement

  • Sensors: Thermistor array and pressure transducer

    • Real-time display to assess steady state conditions

    • Used as input for Voigt fit profile

    • Graphical displays in LabVIEW program

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Optical components distributed feedback laser
Optical ComponentsDistributed Feedback Laser

  • A near infrared (NIR) distributed feedback diode with a fiber-optic output

  • Variable wavelength with a center wavelength of 1571.11 nm

  • Temperature and current controlled

  • Telecomm style component

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Primary Detector

  • Indium Gallium Arsenide (InGaAs) photodiode

  • Light signal detection with gain adjustment from 626 V/A to 18.8X106 V/A

  • Detection of very low light energy levels escaping the cavity during ring down

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Acousto optic modulator
Acousto-Optic Modulator

  • Optical switch allowing energy into cavity

  • 40 MHz acoustic wave causes diffraction of the beam into multiple paths

  • Provides a means to rapidly block beam from atmospheric cell when a resonant condition is achieved

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Mirrors
Mirrors

  • 99.997% reflective cavity mirrors made of UV grade fused silica

  • Create an effective path length of ~100 km

  • Allow for low levels of light to escape for detection

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Lineshape broadening
Lineshape Broadening

  • Measuring the spectral broadening at different T, P will assist ASCENDS researchers with interpreting spectra from aircraft measurements

  • Doppler (Gaussian) broadening, an inhomogeneous and inertial mechanism, depends on temperature

  • Lorentzianbroadening, a homogeneous mechanism, depends on pressure

  • Amount of broadening is characterized by full-width-at-half-maximum (FWHM) values

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Results achieved conditions
ResultsAchieved Conditions

  • Temperature range achieved: -31°C to 23°C

  • Pressure range achieved: 0.1 bar to 1.4 bar

  • Proved feasibility of recreating extreme tropospheric conditions

  • Recorded CRDS spectral data at the T, P points ( ) to the right

  • Recorded spectra at multiple temperatures and fixed pressure and vice versa

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Data points achieved
Data Points Achieved

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Expected results
Expected Results

High Temperature → Larger Width

Low Temperature → Smaller Width

High Pressure → Larger Width

Low Pressure → Smaller Width

Experimental Results

High Temperature → Smaller Width

Low Temperature → Larger Width

High Pressure → Larger Width

Low Pressure → Smaller Width

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Broadening comparisons
Broadening Comparisons

Pressure

Broadening

At fixed T (-30° C)

Temperature Broadening

At fixed P (0.5 bar)

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Conclusions
Conclusions

  • Accurate detection of carbon dioxide through CRDS in order to extract meaningful spectroscopic data has been achieved.

  • Pressure affected broadening much more than temperature over tropospheric ranges for this spectral line.

  • The Whiting approximation provides an accurate description of the spectral shapes for these pressure and temperature ranges.

  • The results of this study will aid NASA ASCENDS researchers

  • CRDS can also provide viable technology for aircraft measurements of local CO2 concentrations.

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Acknowledgements
Acknowledgements

The CSU NASA Laser Team sincerely thanks everyone for all the help we’ve had during this epic journey. A special thanks goes out to Dr. AzerYalin, Jordan Rath, Adam Friss, Isaiah Franka, Brian Lee, and Joshua Taylor. We would also like to thank last year’s team for all of their hard work. Additionally, we would like to thank Dr. Tammy Donahue, Dr. Mitchell Stansloski, and Dan Pierson for giving us great advice along the way. We couldn’t have had the success we had without all of you. Thank you.

Sincerely,

The NASA Laser Team (2012-2013)

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