uncertainty in cloud aerosol transport system (cats) products and measurements presented by patrick...
TRANSCRIPT
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??