Getting a grip on retrieval algorithm uncertainties
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(Getting a grip on) Retrieval algorithm uncertainties. DOE/EU Retrieval workshop Köln, 13.5.2013 Dave Turner Ulrich Löhnert. What types of uncertainties exist? Where do retrieval uncertainties originate from?

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Getting a grip on retrieval algorithm uncertainties

(Getting a grip on)Retrieval algorithm uncertainties

DOE/EU Retrievalworkshop

Köln, 13.5.2013

Dave Turner

Ulrich Löhnert

  • What types of uncertainties exist?

  • Where do retrieval uncertainties originate from?

  • How do we handle the origin of retrieval uncertainties in the retrieval algorithm?

  • Interpretation of Bayesian error estimates


What types of uncertainties exist

Systematic

Random

What types of uncertainties exist?

Temperatureprofilesfrom MWR


Where do retrieval uncertainties originate from

systematic measurement error: Microwave TBs in V band

Where do retrieval uncertainties originate from?


Correct for systematic offsets on average

quasi bias-free

Correct for systematic offsets on average …


Where do retrieval uncertainties originate from1

random measurement error: Microwave TBs in V band

Where do retrieval uncertainties originate from?

constantlook on hotload: ~0.5 K

12 hours


Where do retrieval uncertainties originate from2

random measurement error covariances: TBs in V band

Where do retrieval uncertainties originate from?

fromconstantlook on hotload

instrumentspecific!


Where do retrieval uncertainties originate from3

Limited information content of measurement (“smoothing error”)

Where do retrieval uncertainties originate from?


Where do retrieval uncertainties originate from4

Forward model (systematic & random) error”)

Where do retrieval uncertainties originate from?

Humidity retrieval: Optimal estimation using two different water vapor absorption models

OE uncertainty

prior uncertainty

bias against sondes using

different absorption models


How do we handle the origin of retrieval uncertainties in the algorithm

... OE error”)

Prior information

Measurements

How do we handle the origin of retrieval uncertainties in the algorithm?

Limited information content of measurement (“smoothing error”)

Forward model


Sensitivity of iwc az b retrievals

Forward model uncertainties: error”)Sbmatrix

Sensitivity of IWC = aZb Retrievals

  • Power law relationships used frequently

  • Use in-situ observations to determine the retrieval coefficients a,b by computing Z based upon observed size distribution, habit, etc.

  • There is always scatter in derived a and b

    • “Random” error (i.e., unknown what causes the scatter)

    • Correlated error (variables depend on some other variable such as cloud temperature)

  • What is the impact of the uncertainties in retrieval coefficients on the retrieved IWC?


In situ ice cloud obs from 2000 arm cloud iop coefficients b t and a t
In Situ Ice Cloud error”)Obs From 2000 ARM Cloud IOPCoefficients b(T) and a(T)

b = 2.0

σb = 0.15

Log10(a) = -2.3

σlog10(a) = 0.2

Will simulate IWC using mean a,b values as truth, and investigate the impacts of uncertainties in these coefs








How do we handle the origin of retrieval uncertainties in the algorithm1

... OE error”)

Prior information

Measurements

How do we handle the origin of retrieval uncertainties in the algorithm?

onlyrandom!!!

Limited information content of measurement (“smoothing error”)

Forward model


Interpretation of a and s

Interpretation of error”)A and S


Interpretation of the s and a matrix

Interpretation of the S and A matrix error”)

  • What should we be providing to the end user?

  • Do we need a general (easy-to-understand) documentation for the interpretation of Bayesian algorithms?


Breakout groups on s determination for different instruments

Breakout groups on error”)Sε determination for different instruments?

Radar

MWR

Lidar


Questions for break out groups

  • How to determine diagonal and off-diagonal elements of error”)Sy for the different instruments? (Radar, MWR, Lidar)

  • How can we better describe the uncertainties of the the forward model parameters included in Sb? Need to take a detailed look at forward models for the different instruments.

  • What kind of measurements are needed to improve or better characterize forward model uncertainties?

  • Sεdoes NOT include systematic errors!How do we check for systematic errors in the different instruments? Consistent bias correction procedures?

Questions for break-out groups?


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