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Uncertainty in Cloud Aerosol Transport System (CATS) Products and Measurements

Uncertainty in Cloud Aerosol Transport System (CATS) Products and Measurements. Presented by Patrick Selmer Goddard advisor: Dr. Matthew McGill Assisted by John Yorks. What is CATS?. Doppler Lidar Able to derive wind motion High Spectral Resolution Lidar

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Uncertainty in Cloud Aerosol Transport System (CATS) Products and Measurements

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  1. Uncertainty in Cloud Aerosol Transport System (CATS) Products and Measurements Presented by Patrick Selmer Goddard advisor: Dr. Matthew McGill Assisted by John Yorks

  2. What is CATS? • Doppler Lidar • Able to derive wind motion • High Spectral Resolution Lidar • Able to collect data on cloud and aerosol height, internal structure, and optical properties • Designed for use on high altitude aircraft (ER-2 Superpod) • Currently under development at NASA-Goddard

  3. What is CATS? • Being developed primarily as a demonstrator for NASA’s Aerosol Cloud Ecosystem (ACE) mission • vertical resolution (wind) • 100 m • vertical resolution (aerosol ext.) • 150 m • horizontal resolution (wind) • 10 seconds (~ 2 km) • horizontal resolution (aerosol ext) • 4 seconds (~ 800 m)

  4. Objectives • Derive equations for the uncertainties on aerosol products • Derive equation for the nadir angle in terms of aircraft pitch and roll angles • Derive uncertainty equations for variables involving the nadir angle using this new equation • Calculate uncertainties using simulated atmospheric data and determine if uncertainties are reasonable

  5. Methods Things that are directly measured by CATS Aerosol spectrum, molecular spectrum, doppler shift In addition to these three measurements we also get their uncertainty. This comes from the variance of the photon counts on the detector channels.

  6. Methods Objective 1: Derive equations for the uncertainties on aerosol products • Using the aerosol spectrum and a molecular backscatter profile taken from either a rawinsonde or climatology, we can calculate aerosol products... • Transmissivity • Optical Depth • Extinction • Backscatter • Extinction to backscatter ratio (S-Ratio)

  7. Methods Objective 1: Derive equations for the uncertainties on aerosol products To calculate the uncertainty on these aerosol products, the propagation of error theorem was used... • S2 is the variance • x, u, and v are variables

  8. Methods Objective 1: Derive equations for the uncertainties on aerosol products Example... * Uncertainty in the aerosol spectrum, molecular spectrum, and the wind (doppler shift) comes from instrument limitations.

  9. Methods Objective 2: Derive equation for the nadir angle in terms of aircraft pitch and roll angles Basic Aircraft Flight Dynamics Dizzy? za Nadir Angle Right wing Z-axis, earth relative xa Laser Beam Front of aircraft ya Source of images: Wikipedia – “Flight Dynamics”

  10. Methods Objective 2: Derive equation for the nadir angle in terms of aircraft pitch and roll angles Using Lee et al (1994) as a guide, equation for nadir angle is derived... θ is the nadir angle θo is the nadir angle when there is no roll, pitch or ζ ζ is the angle from the ya axis in the xa,ya plane that the horizontal component of the laser beam is displaced P is the pitch angle R is the roll angle

  11. Methods Objective 3: Derive uncertainty equations for variables involving the nadir angle (θ) using this new equation Z – Axis (Ground Relative) θ LOS H Again, use propagation of error theorem... It gets ugly...

  12. Results Objective 4: Calculate uncertainties using simulated atmospheric data and determine if uncertainties are reasonable Average Percent Error Through Layer Inputted Aircraft Parameters Pitch: 0.0° Roll: 0.0 ° ζ: 0.0 ° θo: 45.0 ° Pitch Error: 1.0 ° Roll Error: 1.0 ° ζ Error: 0.1 ° θo Error: 0.1 ° Z – Axis (Ground Relative) θ Values of errors seem reasonable... LOS H

  13. Results Aerosol Layer – No error in zenith Aerosol Layer – Error in zenith Pitch: 0.0° Roll: 0.0 ° ζ: 0.0 ° θo: 45.0 ° Pitch Error: 1.0 ° Roll Error: 1.0 ° ζ Error: 0.1 ° θo Error: 0.1 °

  14. Results Aerosol Layer Inputted Aircraft Parameters Pitch: 2.0° Roll: 2.0 ° ζ: 2.0 ° θo: 45.0 ° Pitch Error: 1.1 ° Roll Error: 1.1 ° ζ Error: 1.1 ° θo Error: 1.1 ° Savg=5.37 m/s Pitch: 0.0° Roll: 0.0 ° ζ: 0.0 ° θo: 45.0 ° Pitch Error: 0.0° Roll Error: 0.0 ° ζ Error: 0.0 ° θo Error: 0.0 ° Savg=1.42m/s

  15. Summary • Simulated data showed errors of around 14% or less of actual value of S-Ratio • Error induced in horizontal wind measurement by error in aircraft angles can be significant • Much more work to be done • Addition of solar background, noise • Instrument needs more testing • Test flight demonstration in October 2010??

  16. Acknowledgements Matt McGill John Yorks Research and Discover: George Hurtt Karen Burnett-Kurie NASA

  17. References Lee, W., Dodge, P., Marks, F. D., & Hildebrand, P. H. (1994). Notes and Correspondence: Mapping of Airborne Doppler Radar Data. Journal of Atmospheric and Oceanic Technology, 11, 572-578. Information related to CATS: Matt McGill and John Yorks

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