Dear Randy
My question is perhaps the same as Jim's. The question is, how is this number
interpreted, by those who use it? In what way does it quantify the error?
Best wishes
Jonathan
----- Forwarded message from "rhorne at excaliburlabs.com" <rhorne at excaliburlabs.com> -----
> Date: Fri, 5 Jul 2013 13:43:25 -0400
> From: "rhorne at excaliburlabs.com" <rhorne at excaliburlabs.com>
> To: Jim Biard <jim.biard at noaa.gov>,
> "cf-metadata at cgd.ucar.edu List" <cf-metadata at cgd.ucar.edu>
> Subject: Re: [CF-metadata] how to represent a non-standard error
>
>
>
> Jim:
>
>
>
> An expected error value is individually calculated for EACH wind vector in
> the product file based on the factors I identified a few emails back.
>
>
>
> This expected error allows the users of the GOES-R derived motion wind
> products to know what the error is for each wind vector in the product
> file. I think there are weather prediction models that make use of these
> error values. There may be other uses, but I don't know for sure.
>
>
>
>
>
> very respectfully,
>
>
>
> randy
>
> ----------------------------------------
> From: "Jim Biard" <jim.biard at noaa.gov>
> Sent: Friday, July 05, 2013 1:22 PM
> To: "cf-metadata at cgd.ucar.edu List" <cf-metadata at cgd.ucar.edu>
> Cc: "rhorne at excaliburlabs.com Horne" <rhorne at excaliburlabs.com>
> Subject: Re: [CF-metadata] how to represent a non-standard error
>
> Randy,
> Thanks. I guess I'm still wondering how you can validly assign a label
> such as "error" to a number that doesn't somehow tell you the likelihood of
> the variable value being within some sort of interval. Without getting too
> hung up on statistical formalisms, can you explain what use this number is
> to you?
> Grace and peace,
> Jim
> Jim Biard
> Research Scholar
> Cooperative Institute for Climate and Satellites
> Remote Sensing and Applications Division
> National Climatic Data Center
> 151 Patton Ave, Asheville, NC 28801-5001
>
> jim.biard at noaa.gov
> 828-271-4900
> Follow us on Facebook!
> On Jul 5, 2013, at 1:13 PM, rhorne at excaliburlabs.com wrote:
>
> Jim:
>
> The magnitude of the Expected Error is a function of the calculated wind
> speed.
>
> In perusing the Expected Error algorithm documentation to compose the last
> email, it appears the algorithm does not assume any type of an error
> distribution (normal or otherwise). The error estimate is absolute and is
> not associated with a confidence level.
>
> The use of this algorithm is based on the results it has achieved on
> predecessor weather satellite programs (empirical data has been used to
> determine its effectiveness.) I can provide you additional information on
> the Expected Error algorithm if you are interested,
>
> The point I am trying to make is that this is a specific error estimation
> approach that is unrelated to a sampling distribution. I would think
> there are others.
>
> very respectfully,
>
> randy
>
> From: "Jim Biard" <jim.biard at noaa.gov>
> Sent: Friday, July 05, 2013 11:22 AM
> To: "cf-metadata at cgd.ucar.edu List" <cf-metadata at cgd.ucar.edu>
> Cc: "rhorne at excaliburlabs.com Horne" <rhorne at excaliburlabs.com>
> Subject: Re: [CF-metadata] Fwd: how to represent a non-standard error
>
> Randy,
> Could you help me understand a touch more about this? You say it is an
> error that comes from a custom algorithm, but what defines what magnitude
> it has? How do you relate it to anything? Does it represent some sort of
> confidence interval?
> Grace and peace,
> Jim
> Jim Biard
> Research Scholar
> Cooperative Institute for Climate and Satellites
> Remote Sensing and Applications Division
> National Climatic Data Center
> 151 Patton Ave, Asheville, NC 28801-5001
>
> jim.biard at noaa.gov
> 828-271-4900
> <CicsLogoTiny.png>Follow us on Facebook!
> On Jul 5, 2013, at 9:28 AM, "rhorne at excaliburlabs.com"
> <rhorne at excaliburlabs.com> wrote:
>
> Dear Jonathan:
>
> In the case of the GOES-R derived motion winds product, the error estimate
> (i.e. more formally referred to as Expected Error) is based on a custom
> algorithm.
>
> This expected error algorithm is specific to atmospheric wind vectors
> derived from satellte data. The overarching concept of the wind algorithms
> generated from satellite data is doing pattern matching of phenomena (like
> clouds) across multiple images of the same region separated by some period
> of time
>
> The GOES-R incarnation of this Expected Error approach makes use of a set
> of error predictors including (1) NWP model data (wind shear, temperature
> gradient), (2) wind speed, direction, and consistency quality indicators
> output from the winds algorithm proper, and (3) a wavelength dependent
> constants (GOES-R generates sets of wind vectors from a visible and several
> emissive bands)
>
> I also found an article on the web that discusses it:
>
> https://www.eumetsat.int/cs/idcplg?IdcService=GET_FILE&dDocName=pdf_conf_p42
> _s2_le_marshall&allowInterrupt=1&noSaveAs=1&RevisionSelectionMethod=LatestRe
> leased
>
> very respectfully,
>
> randy
>
> Dear all
>
> OK, I agree that if it's useful to compare them, then they should be
> described
> in a standardised way.
>
> Why is this *not* a standard error? I suppose that to be described as a
> standard error it should be a number you could regard as the standard
> deviation
> of the true value around the stated value. If it's not that, are there
> other
> ways you would use such a number?
>
> Best wishes
>
> Jonathan
>
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----- End forwarded message -----
Received on Mon Jul 08 2013 - 13:12:52 BST
