Uncertainty in Cloud Aerosol Transport System (CATS)

Products and Measurements

Presented by Patrick SelmerGoddard advisor: Dr. Matthew McGill

Assisted by John Yorks

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

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)

Objectives

1) Derive equations for the uncertainties on aerosol products

2) Derive equation for the nadir angle in terms of aircraft pitch and roll angles

3) Derive uncertainty equations for variables involving the nadir angle using this new equation

4) Calculate uncertainties using simulated atmospheric data and determine if uncertainties are reasonable

MethodsThings that are directly measured by CATSAerosol 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.

Methods

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)

Objective 1: Derive equations for the uncertainties on aerosol products

Methods

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

Objective 1: Derive equations for the uncertainties on aerosol products

Methods

Example...

* Uncertainty in the aerosol spectrum, molecular spectrum, and the wind (doppler shift) comes from instrument

limitations.

Objective 1: Derive equations for the uncertainties on aerosol products

Methods

Source of images: Wikipedia – “Flight Dynamics”

Basic Aircraft Flight Dynamics Dizzy?

Objective 2: Derive equation for the nadir angle in terms of aircraft pitch and roll angles

za

ya

xa

Front of aircraft

Right wing

Z-ax

is, e

arth

rela

tive

Nadir A

ngle

Laser Beam

Methods

Using Lee et al (1994) as a guide, equation for nadir angle is derived...

θ is the nadir angleθo is the nadir angle when there is no roll, pitch or ζζ is the angle from the ya axis in the xa,ya plane that the horizontal component of the laser beam is displacedP is the pitch angleR is the roll angle

Objective 2: Derive equation for the nadir angle in terms of aircraft pitch and roll angles

Methods

θ LOS

H

Z –

Axis

(Gro

und

Rela

tive)

Objective 3: Derive uncertainty equations for variables involving the nadir angle (θ) using this new equation

Again, use propagation of error theorem...

It gets ugly...

Results

Average Percent Error Through LayerPitch: 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 °

Inputted Aircraft Parameters

θ LOS

H

Z –

Axis

(Gro

und

Rela

tive)

Values of errors seem reasonable...

Objective 4: Calculate uncertainties using simulated atmospheric data and determine if uncertainties are reasonable

Ttot2secθ Ta

2secθ τa S-Ratioa

Cirrus 10.1 10.1 22.2 10.2

Cumulus 11.4 11.5 14.6 14.4

Aerosol 10.2 10.2 40.2 13.5

Clear 10.0 10.0 408.8 151.8

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 °

ResultsAerosol Layer

Inputted Aircraft ParametersPitch: 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 °

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=5.37 m/s

Savg=1.42m/s

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??

Acknowledgements

Matt McGillJohn Yorks

Research and Discover:George Hurtt

Karen Burnett-KurieNASA

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

References